to #26323588

commit 18c9a6bbe0645a05172a900740b9d2d379d54320 upstream.

This function will be used in a later patch to switch the struct
request_queue q_usage_counter from killed back to live. In contrast
to percpu_ref_reinit(), this new function does not require that the
refcount is zero.
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Acked-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 96fd84d83a778450ffae737d9efa546ac3983b1f upstream.

Null check kfree is redundant, so remove it.
This is detected by coccinelle.
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit fddafacee287b3140212c92464077e971401f860 upstream.

This adds IORING_OP_SEND for send(2) support, and IORING_OP_RECV for
recv(2) support.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 2550878f8421f7912fdd56b38c630b797f95c749 upstream.

io_wq workers use io_issue_sqe() to forward sqes and never
io_queue_sqe(). Remove extra check for io_wq_current_is_worker()
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit caf582c652feccd42c50923f0467c4f2dcef279e upstream.

It should be pretty rare to not submitting anything when there is
something in the ring. No need to keep heuristics for this case.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit ee7d46d9db19ded7b7222af95add63606318a480 upstream.

A user may ask to submit more than there is in the ring, and then
io_uring will submit as much as it can. However, in the last iteration
it will allocate an io_kiocb and immediately free it. It could do
better and adjust @to_submit to what is in the ring.

And since the ring's head is already checked here, there is no need to
do it in the loop, spamming with smp_load_acquire()'s barriers
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 9ef4f124894b7b9241a3cf5f9b40db0812783d66 upstream.

Make io_submit_sqes() to clamp @to_submit itself. It removes duplicated
code and prepares for following changes.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 8110c1a6212e430a84edd2b83fe9043def8b743e upstream.

Some applications like to start small in terms of ring size, and then
ramp up as needed. This is a bit tricky to do currently, since we don't
advertise the max ring size.

This adds IORING_SETUP_CLAMP. If set, and the values for SQ or CQ ring
size exceed what we support, then clamp them at the max values instead
of returning -EINVAL. Since we return the chosen ring sizes after setup,
no further changes are needed on the application side. io_uring already
changes the ring sizes if the application doesn't ask for power-of-two
sizes, for example.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit c6ca97b30c47c7ad36107d3764bb4dc37026d171 upstream.

Currently we only batch free if fixed files are used, no links, no aux
data, etc. This extends the batch freeing to only exclude the linked
case and fallback case, and make io_free_req_many() handle the other
cases just fine.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 8237e045983d82ba78eaab5f60b9300927fc6796 upstream.

This cleans up the code a bit, and it allows us to build on top of the
multi-req freeing.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 2b85edfc0c90efc68dea3d665bb4111bf0694e05 upstream.

percpu_ref_tryget() has its own overhead. Instead getting a reference
for each request, grab a bunch once per io_submit_sqes().

~5% throughput boost for a "submit and wait 128 nops" benchmark.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>

__io_req_free_empty() -> __io_req_do_free()
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 4e5ef02317b12e2ed3d604281ffb6b75261f7612 upstream.

Add percpu_ref_tryget_many(), which works the same way as
percpu_ref_tryget(), but grabs specified number of refs.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NDennis Zhou <dennis@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit c1ca757bd6f4632c510714631ddcc2d13030fe1e upstream.

This adds support for doing madvise(2) through io_uring. We assume that
any operation can block, and hence punt everything async. This could be
improved, but hard to make bullet proof. The async punt ensures it's
safe.
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit db08ca25253d56f1f76eb4b3fe32a7ac1fbab741 upstream.

This is in preparation for enabling this functionality through io_uring.
Add a helper that is just exporting what sys_madvise() does, and have the
system call use it.

No functional changes in this patch.
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 4840e418c2fc533d55ff6caa5b9313eed1d26cfd upstream.

This adds support for doing fadvise through io_uring. We assume that
WILLNEED doesn't block, but that DONTNEED may block.
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit ba04291eb66ed895f194ae5abd3748d72bf8aaea upstream.

This behaves like preadv2/pwritev2 with offset == -1, it'll use (and
update) the current file position. This obviously comes with the caveat
that if the application has multiple read/writes in flight, then the
end result will not be as expected. This is similar to threads sharing
a file descriptor and doing IO using the current file position.

Since this feature isn't easily detectable by doing a read or write,
add a feature flags, IORING_FEAT_RW_CUR_POS, to allow applications to
detect presence of this feature.
Reported-by: N李通洲 <carter.li@eoitek.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 3a6820f2bb8a079975109c25a5d1f29f46bce5d2 upstream.

For uses cases that don't already naturally have an iovec, it's easier
(or more convenient) to just use a buffer address + length. This is
particular true if the use case is from languages that want to create
a memory safe abstraction on top of io_uring, and where introducing
the need for the iovec may impose an ownership issue. For those cases,
they currently need an indirection buffer, which means allocating data
just for this purpose.

Add basic read/write that don't require the iovec.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit e94f141bd248ebdadcb7351f1e70b31cee5add53 upstream.

For busy IORING_OP_POLL_ADD workloads, we can have enough contention
on the completion lock that we fail the inline completion path quite
often as we fail the trylock on that lock. Add a list for deferred
completions that we can use in that case. This helps reduce the number
of async offloads we have to do, as if we get multiple completions in
a row, we'll piggy back on to the poll_llist instead of having to queue
our own offload.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit ad3eb2c89fb24d14ac81f43eff8e85fece2c934d upstream.

We currently check ->cq_overflow_list from both SQ and CQ context, which
causes some bouncing of that cache line. Add separate bits of state for
this instead, so that the SQ side can check using its own state, and
likewise for the CQ side.

This adds ->sq_check_overflow with the SQ state, and ->cq_check_overflow
with the CQ state. If we hit an overflow condition, both of these bits
are set. Likewise for overflow flush clear, we clear both bits. For the
fast path of just checking if there's an overflow condition on either
the SQ or CQ side, we can use our own private bit for this.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit d3656344fea0339fb0365c8df4d2beba4e0089cd upstream.

We currently have various switch statements that check if an opcode needs
a file, mm, etc. These are hard to keep in sync as opcodes are added. Add
a struct io_op_def that holds all of this information, so we have just
one spot to update when opcodes are added.

This also enables us to NOT allocate req->io if a deferred command
doesn't need it, and corrects some mistakes we had in terms of what
commands need mm context.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit add7b6b85a4dfa89283834d181e87ea2144b9028 upstream.

__io_free_req() and io_double_put_req() aren't used before they are
defined, so we can kill these two forwards.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 32fe525b6d10fec956cfe68f0db76839cd7f0ea5 upstream.

Move io_queue_link_head() to links handling code in io_submit_sqe(),
so it wouldn't need extra checks and would have better data locality.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 9d76377f7e13c19441fdd066033345289f89b5fe upstream.

Calling "prev" a head of a link is a bit misleading. Rename it
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit ce35a47a3a0208a77b4d31b7f2e8ed57d624093d upstream.

io_uring defaults to always doing inline submissions, if at all
possible. But for larger copies, even if the data is fully cached, that
can take a long time. Add an IOSQE_ASYNC flag that the application can
set on the SQE - if set, it'll ensure that we always go async for those
kinds of requests. Use the io-wq IO_WQ_WORK_CONCURRENT flag to ensure we
get the concurrency we desire for this case.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commmit 895e2ca0f693c672902191747b548bdc56f0c7de upstream.

io-wq assumes that work will complete fast (and not block), so it
doesn't create a new worker when work is enqueued, if we already have
at least one worker running. This is done on the assumption that if work
is running, then it will complete fast.

Add an option to force io-wq to fork a new worker for work queued. This
is signaled by setting IO_WQ_WORK_CONCURRENT on the work item. For that
case, io-wq will create a new worker, even though workers are already
running.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit eddc7ef52a6b37b7ba3d1c8a8fbb63d5d9914f8a upstream.

This provides support for async statx(2) through io_uring.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 3934e36f6099e6277db33f433fe135c6644e8ac2 upstream.

To implement an async stat, we need to provide the flags mapping and
the statx user copy. Make them available internally, through
fs/internal.h.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

We currently fully quiesce the ring before an unregister or update of
the fixed fileset. This is very expensive, and we can be a bit smarter
about this.

Add a percpu refcount for the file tables as a whole. Grab a percpu ref
when we use a registered file, and put it on completion. This is cheap
to do. Upon removal of a file from a set, switch the ref count to atomic
mode. When we hit zero ref on the completion side, then we know we can
drop the previously registered files. When the old files have been
dropped, switch the ref back to percpu mode for normal operation.

Since there's a period between doing the update and the kernel being
done with it, add a IORING_OP_FILES_UPDATE opcode that can perform the
same action. The application knows the update has completed when it gets
the CQE for it. Between doing the update and receiving this completion,
the application must continue to use the unregistered fd if submitting
IO on this particular file.

This takes the runtime of test/file-register from liburing from 14s to
about 0.7s.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 214828962dead0c698f92b60ef97ce3c5fc2c8fe upstream.

Percpu reference counters should now be initialized with the
PERCPU_REF_ALLOW_REINIT in order to allow switching them to the
percpu mode from the atomic mode. This is exactly what
percpu_ref_reinit() called from __io_uring_register() is supposed to
do. So let's initialize percpu refcounters with the
PERCU_REF_ALLOW_REINIT flag.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NDennis Zhou <dennis@kernel.org>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 7d9ab9b6adffd9c474c1274acb5f6208f9a09cf3 upstream.

Release percpu memory after finishing the switch to the atomic mode
if only PERCPU_REF_ALLOW_REINIT isn't set.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NDennis Zhou <dennis@kernel.org>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 09ed79d6d75f06cc963a78f25463251b0a758dc7 upstream.

In most cases percpu reference counters are not switched to the
percpu mode after they reach the atomic mode. Some obvious exceptions
are reference counters which are initialized into the atomic
mode (using PERCPU_REF_INIT_ATOMIC and PERCPU_REF_INIT_DEAD flags),
and there are few other exceptions.

But in most cases there is no way back, and once the reference counter
is switched to the atomic mode, there is no reason to wait for
percpu_ref_exit() to release the percpu memory. Of course, the size
of a single counter is not so big, but because it can pin the whole
percpu block in memory, the memory footprint can be noticeable
(e.g. on my 32 CPUs machine a percpu block is 8Mb large).

To make releasing of the percpu memory as early as possible, let's
introduce the PERCPU_REF_ALLOW_REINIT flag with the following semantics:
it has to be set in order to switch a percpu reference counter to the
percpu mode after the initialization. PERCPU_REF_INIT_ATOMIC and
PERCPU_REF_INIT_DEAD flags will implicitly assume PERCPU_REF_ALLOW_REINIT.

This patch doesn't introduce any functional change to avoid any
regressions. It will be done later in the patchset after adjusting
all call sites, which are reviving percpu counters.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NDennis Zhou <dennis@kernel.org>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit b5dba59e0cf7e2cc4d3b3b1ac5fe81ddf21959eb upstream.

This works just like close(2), unsurprisingly. We remove the file
descriptor and post the completion inline, then offload the actual
(potential) last file put to async context.

Mark the async part of this work as uncancellable, as we really must
guarantee that the latter part of the close is run.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

Cherry-pick from commit 80cd795630d6526ba729a089a435bf74a57af927 upstream.

44d8047f1d8 ("binder: use standard functions to allocate fds")
exposed a pre-existing issue in the binder driver.

fdget() is used in ksys_ioctl() as a performance optimization.
One of the rules associated with fdget() is that ksys_close() must
not be called between the fdget() and the fdput(). There is a case
where this requirement is not met in the binder driver which results
in the reference count dropping to 0 when the device is still in
use. This can result in use-after-free or other issues.

If userpace has passed a file-descriptor for the binder driver using
a BINDER_TYPE_FDA object, then kys_close() is called on it when
handling a binder_ioctl(BC_FREE_BUFFER) command. This violates
the assumptions for using fdget().

The problem is fixed by deferring the close using task_work_add(). A
new variant of __close_fd() was created that returns a struct file
with a reference. The fput() is deferred instead of using ksys_close().

Fixes: 44d8047f1d87a ("binder: use standard functions to allocate fds")
Suggested-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NTodd Kjos <tkjos@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 0c9d5ccd26a004f59333c06fbbb98f9cb1eed93d upstream.

Not all work can be cancelled, some of it we may need to guarantee
that it runs to completion. Allow the caller to set IO_WQ_WORK_NO_CANCEL
on work that must not be cancelled. Note that the caller work function
must also check for IO_WQ_WORK_NO_CANCEL on work that is marked
IO_WQ_WORK_CANCEL.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 15b71abe7b52df214785dde0de9f581cc0216d17 upstream.

This works just like openat(2), except it can be performed async. For
the normal case of a non-blocking path lookup this will complete
inline. If we have to do IO to perform the open, it'll be done from
async context.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit 35cb6d54c1d5daf1d1ed585ef5ce4557e7ab284c upstream.

This is a prep patch for supporting non-blocking open from io_uring.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit b28a10aedcd4d175470171a32f4f20b0a60a612b upstream.

Test all of the various openat2(2) flags. A small stress-test of a
symlink-rename attack is included to show that the protections against
".."-based attacks are sufficient.

The main things these self-tests are enforcing are:

  * The struct+usize ABI for openat2(2) and copy_struct_from_user() to
    ensure that upgrades will be handled gracefully (in addition,
    ensuring that misaligned structures are also handled correctly).

  * The -EINVAL checks for openat2(2) are all correctly handled to avoid
    userspace passing unknown or conflicting flag sets (most
    importantly, ensuring that invalid flag combinations are checked).

  * All of the RESOLVE_* semantics (including errno values) are
    correctly handled with various combinations of paths and flags.

  * RESOLVE_IN_ROOT correctly protects against the symlink rename(2)
    attack that has been responsible for several CVEs (and likely will
    be responsible for several more).

Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: NAleksa Sarai <cyphar@cyphar.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit fddb5d430ad9fa91b49b1d34d0202ffe2fa0e179 upstream.

/* Background. */
For a very long time, extending openat(2) with new features has been
incredibly frustrating. This stems from the fact that openat(2) is
possibly the most famous counter-example to the mantra "don't silently
accept garbage from userspace" -- it doesn't check whether unknown flags
are present[1].

This means that (generally) the addition of new flags to openat(2) has
been fraught with backwards-compatibility issues (O_TMPFILE has to be
defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old
kernels gave errors, since it's insecure to silently ignore the
flag[2]). All new security-related flags therefore have a tough road to
being added to openat(2).

Userspace also has a hard time figuring out whether a particular flag is
supported on a particular kernel. While it is now possible with
contemporary kernels (thanks to [3]), older kernels will expose unknown
flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during
openat(2) time matches modern syscall designs and is far more
fool-proof.

In addition, the newly-added path resolution restriction LOOKUP flags
(which we would like to expose to user-space) don't feel related to the
pre-existing O_* flag set -- they affect all components of path lookup.
We'd therefore like to add a new flag argument.

Adding a new syscall allows us to finally fix the flag-ignoring problem,
and we can make it extensible enough so that we will hopefully never
need an openat3(2).

/* Syscall Prototype. */
  /*
   * open_how is an extensible structure (similar in interface to
   * clone3(2) or sched_setattr(2)). The size parameter must be set to
   * sizeof(struct open_how), to allow for future extensions. All future
   * extensions will be appended to open_how, with their zero value
   * acting as a no-op default.
   */
  struct open_how { /* ... */ };

  int openat2(int dfd, const char *pathname,
              struct open_how *how, size_t size);

/* Description. */
The initial version of 'struct open_how' contains the following fields:

  flags
    Used to specify openat(2)-style flags. However, any unknown flag
    bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR)
    will result in -EINVAL. In addition, this field is 64-bits wide to
    allow for more O_ flags than currently permitted with openat(2).

  mode
    The file mode for O_CREAT or O_TMPFILE.

    Must be set to zero if flags does not contain O_CREAT or O_TMPFILE.

  resolve
    Restrict path resolution (in contrast to O_* flags they affect all
    path components). The current set of flags are as follows (at the
    moment, all of the RESOLVE_ flags are implemented as just passing
    the corresponding LOOKUP_ flag).

    RESOLVE_NO_XDEV       => LOOKUP_NO_XDEV
    RESOLVE_NO_SYMLINKS   => LOOKUP_NO_SYMLINKS
    RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS
    RESOLVE_BENEATH       => LOOKUP_BENEATH
    RESOLVE_IN_ROOT       => LOOKUP_IN_ROOT

open_how does not contain an embedded size field, because it is of
little benefit (userspace can figure out the kernel open_how size at
runtime fairly easily without it). It also only contains u64s (even
though ->mode arguably should be a u16) to avoid having padding fields
which are never used in the future.

Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE
is no longer permitted for openat(2). As far as I can tell, this has
always been a bug and appears to not be used by userspace (and I've not
seen any problems on my machines by disallowing it). If it turns out
this breaks something, we can special-case it and only permit it for
openat(2) but not openat2(2).

After input from Florian Weimer, the new open_how and flag definitions
are inside a separate header from uapi/linux/fcntl.h, to avoid problems
that glibc has with importing that header.

/* Testing. */
In a follow-up patch there are over 200 selftests which ensure that this
syscall has the correct semantics and will correctly handle several
attack scenarios.

In addition, I've written a userspace library[4] which provides
convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary
because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care
must be taken when using RESOLVE_IN_ROOT'd file descriptors with other
syscalls). During the development of this patch, I've run numerous
verification tests using libpathrs (showing that the API is reasonably
usable by userspace).

/* Future Work. */
Additional RESOLVE_ flags have been suggested during the review period.
These can be easily implemented separately (such as blocking auto-mount
during resolution).

Furthermore, there are some other proposed changes to the openat(2)
interface (the most obvious example is magic-link hardening[5]) which
would be a good opportunity to add a way for userspace to restrict how
O_PATH file descriptors can be re-opened.

Another possible avenue of future work would be some kind of
CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace
which openat2(2) flags and fields are supported by the current kernel
(to avoid userspace having to go through several guesses to figure it
out).

[1]: https://lwn.net/Articles/588444/
[2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com
[3]: commit 629e014b ("fs: completely ignore unknown open flags")
[4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523
[5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/
[6]: https://youtu.be/ggD-eb3yPVsSuggested-by: NChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: NAleksa Sarai <cyphar@cyphar.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit f5a1a536fa14895ccff4e94e6a5af90901ce86aa upstream.

A common pattern for syscall extensions is increasing the size of a
struct passed from userspace, such that the zero-value of the new fields
result in the old kernel behaviour (allowing for a mix of userspace and
kernel vintages to operate on one another in most cases).

While this interface exists for communication in both directions, only
one interface is straightforward to have reasonable semantics for
(userspace passing a struct to the kernel). For kernel returns to
userspace, what the correct semantics are (whether there should be an
error if userspace is unaware of a new extension) is very
syscall-dependent and thus probably cannot be unified between syscalls
(a good example of this problem is [1]).

Previously there was no common lib/ function that implemented
the necessary extension-checking semantics (and different syscalls
implemented them slightly differently or incompletely[2]). Future
patches replace common uses of this pattern to make use of
copy_struct_from_user().

Some in-kernel selftests that insure that the handling of alignment and
various byte patterns are all handled identically to memchr_inv() usage.

[1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
     robustify sched_read_attr() ABI logic and code")

[2]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
     similar checks to copy_struct_from_user() while rt_sigprocmask(2)
     always rejects differently-sized struct arguments.
Suggested-by: NRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: NAleksa Sarai <cyphar@cyphar.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NChristian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191001011055.19283-2-cyphar@cyphar.comSigned-off-by: NChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

to #26323588

commit ab87f9a56c8ee9fa6856cb13d8f2905db913baae upstream.

Allow LOOKUP_BENEATH and LOOKUP_IN_ROOT to safely permit ".." resolution
(in the case of LOOKUP_BENEATH the resolution will still fail if ".."
resolution would resolve a path outside of the root -- while
LOOKUP_IN_ROOT will chroot(2)-style scope it). Magic-link jumps are
still disallowed entirely[*].

As Jann explains[1,2], the need for this patch (and the original no-".."
restriction) is explained by observing there is a fairly easy-to-exploit
race condition with chroot(2) (and thus by extension LOOKUP_IN_ROOT and
LOOKUP_BENEATH if ".." is allowed) where a rename(2) of a path can be
used to "skip over" nd->root and thus escape to the filesystem above
nd->root.

  thread1 [attacker]:
    for (;;)
      renameat2(AT_FDCWD, "/a/b/c", AT_FDCWD, "/a/d", RENAME_EXCHANGE);
  thread2 [victim]:
    for (;;)
      openat2(dirb, "b/c/../../etc/shadow",
              { .flags = O_PATH, .resolve = RESOLVE_IN_ROOT } );

With fairly significant regularity, thread2 will resolve to
"/etc/shadow" rather than "/a/b/etc/shadow". There is also a similar
(though somewhat more privileged) attack using MS_MOVE.

With this patch, such cases will be detected *during* ".." resolution
and will return -EAGAIN for userspace to decide to either retry or abort
the lookup. It should be noted that ".." is the weak point of chroot(2)
-- walking *into* a subdirectory tautologically cannot result in you
walking *outside* nd->root (except through a bind-mount or magic-link).
There is also no other way for a directory's parent to change (which is
the primary worry with ".." resolution here) other than a rename or
MS_MOVE.

The primary reason for deferring to userspace with -EAGAIN is that an
in-kernel retry loop (or doing a path_is_under() check after re-taking
the relevant seqlocks) can become unreasonably expensive on machines
with lots of VFS activity (nfsd can cause lots of rename_lock updates).
Thus it should be up to userspace how many times they wish to retry the
lookup -- the selftests for this attack indicate that there is a ~35%
chance of the lookup succeeding on the first try even with an attacker
thrashing rename_lock.

A variant of the above attack is included in the selftests for
openat2(2) later in this patch series. I've run this test on several
machines for several days and no instances of a breakout were detected.
While this is not concrete proof that this is safe, when combined with
the above argument it should lend some trustworthiness to this
construction.

[*] It may be acceptable in the future to do a path_is_under() check for
    magic-links after they are resolved. However this seems unlikely to
    be a feature that people *really* need -- it can be added later if
    it turns out a lot of people want it.

[1]: https://lore.kernel.org/lkml/CAG48ez1jzNvxB+bfOBnERFGp=oMM0vHWuLD6EULmne3R6xa53w@mail.gmail.com/
[2]: https://lore.kernel.org/lkml/CAG48ez30WJhbsro2HOc_DR7V91M+hNFzBP5ogRMZaxbAORvqzg@mail.gmail.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: NJann Horn <jannh@google.com>
Suggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NAleksa Sarai <cyphar@cyphar.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>