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  1. 24 1月, 2021 9 次提交
  3. 11 12月, 2020 1 次提交
  5. 10 12月, 2020 1 次提交
  7. 25 9月, 2020 1 次提交
  9. 28 8月, 2020 1 次提交
  11. 15 8月, 2020 1 次提交
  13. 13 8月, 2020 3 次提交
    • K
      exec: move path_noexec() check earlier · 0fd338b2
      由 Kees Cook 提交于 
      The path_noexec() check, like the regular file check, was happening too
late, letting LSMs see impossible execve()s.  Check it earlier as well in
may_open() and collect the redundant fs/exec.c path_noexec() test under
the same robustness comment as the S_ISREG() check.

My notes on the call path, and related arguments, checks, etc:

do_open_execat()
    struct open_flags open_exec_flags = {
        .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
        .acc_mode = MAY_EXEC,
        ...
    do_filp_open(dfd, filename, open_flags)
        path_openat(nameidata, open_flags, flags)
            file = alloc_empty_file(open_flags, current_cred());
            do_open(nameidata, file, open_flags)
                may_open(path, acc_mode, open_flag)
                    /* new location of MAY_EXEC vs path_noexec() test */
                    inode_permission(inode, MAY_OPEN | acc_mode)
                        security_inode_permission(inode, acc_mode)
                vfs_open(path, file)
                    do_dentry_open(file, path->dentry->d_inode, open)
                        security_file_open(f)
                        open()
    /* old location of path_noexec() test */
Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: http://lkml.kernel.org/r/20200605160013.3954297-4-keescook@chromium.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      0fd338b2
    • K
      exec: move S_ISREG() check earlier · 633fb6ac
      由 Kees Cook 提交于 
      The execve(2)/uselib(2) syscalls have always rejected non-regular files.
Recently, it was noticed that a deadlock was introduced when trying to
execute pipes, as the S_ISREG() test was happening too late.  This was
fixed in commit 73601ea5 ("fs/open.c: allow opening only regular files
during execve()"), but it was added after inode_permission() had already
run, which meant LSMs could see bogus attempts to execute non-regular
files.

Move the test into the other inode type checks (which already look for
other pathological conditions[1]).  Since there is no need to use
FMODE_EXEC while we still have access to "acc_mode", also switch the test
to MAY_EXEC.

Also include a comment with the redundant S_ISREG() checks at the end of
execve(2)/uselib(2) to note that they are present to avoid any mistakes.

My notes on the call path, and related arguments, checks, etc:

do_open_execat()
    struct open_flags open_exec_flags = {
        .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
        .acc_mode = MAY_EXEC,
        ...
    do_filp_open(dfd, filename, open_flags)
        path_openat(nameidata, open_flags, flags)
            file = alloc_empty_file(open_flags, current_cred());
            do_open(nameidata, file, open_flags)
                may_open(path, acc_mode, open_flag)
		    /* new location of MAY_EXEC vs S_ISREG() test */
                    inode_permission(inode, MAY_OPEN | acc_mode)
                        security_inode_permission(inode, acc_mode)
                vfs_open(path, file)
                    do_dentry_open(file, path->dentry->d_inode, open)
                        /* old location of FMODE_EXEC vs S_ISREG() test */
                        security_file_open(f)
                        open()

[1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: http://lkml.kernel.org/r/20200605160013.3954297-3-keescook@chromium.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      633fb6ac
    • A
      fix breakage in do_rmdir() · 24fb33d4
      由 Al Viro 提交于 
      syzbot reported and bisected a use-after-free due to the recent init
cleanups.

The putname() should happen only after we'd *not* branched to retry,
same as it's done in do_unlinkat().

Reported-by: syzbot+bbeb1c88016c7db4aa24@syzkaller.appspotmail.com
Fixes: e24ab0ef "fs: push the getname from do_rmdir into the callers"
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      24fb33d4
  15. 31 7月, 2020 5 次提交
  17. 09 6月, 2020 2 次提交
    • L
      vfs: clean up posix_acl_permission() logic aroudn MAY_NOT_BLOCK · 63d72b93
      由 Linus Torvalds 提交于 
      posix_acl_permission() does not care about MAY_NOT_BLOCK, and in fact
the permission logic internally must not check that bit (it's only for
upper layers to decide whether they can block to do IO to look up the
acl information or not).

But the way the code was written, it _looked_ like it cared, since the
function explicitly did not mask that bit off.

But it has exactly two callers: one for when that bit is set, which
first clears the bit before calling posix_acl_permission(), and the
other call site when that bit was clear.

So stop the silly games "saving" the MAY_NOT_BLOCK bit that must not be
used for the actual permission test, and that currently is pointlessly
cleared by the callers when the function itself should just not care.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      63d72b93
    • L
      vfs: do not do group lookup when not necessary · 5fc475b7
      由 Linus Torvalds 提交于 
      Rasmus Villemoes points out that the 'in_group_p()' tests can be a
noticeable expense, and often completely unnecessary.  A common
situation is that the 'group' bits are the same as the 'other' bits
wrt the permissions we want to test.

So rewrite 'acl_permission_check()' to not bother checking for group
ownership when the permission check doesn't care.

For example, if we're asking for read permissions, and both 'group' and
'other' allow reading, there's really no reason to check if we're part
of the group or not: either way, we'll allow it.

Rasmus says:
 "On a bog-standard Ubuntu 20.04 install, a workload consisting of
  compiling lots of userspace programs (i.e., calling lots of
  short-lived programs that all need to get their shared libs mapped in,
  and the compilers poking around looking for system headers - lots of
  /usr/lib, /usr/bin, /usr/include/ accesses) puts in_group_p around
  0.1% according to perf top.

  System-installed files are almost always 0755 (directories and
  binaries) or 0644, so in most cases, we can avoid the binary search
  and the cost of pulling the cred->groups array and in_group_p() .text
  into the cpu cache"
Reported-by: NRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5fc475b7
  19. 14 5月, 2020 1 次提交
    • M
      vfs: allow unprivileged whiteout creation · a3c751a5
      由 Miklos Szeredi 提交于 
      Whiteouts, unlike real device node should not require privileges to create.

The general concern with device nodes is that opening them can have side
effects.  The kernel already avoids zero major (see
Documentation/admin-guide/devices.txt).  To be on the safe side the patch
explicitly forbids registering a char device with 0/0 number (see
cdev_add()).

This guarantees that a non-O_PATH open on a whiteout will fail with ENODEV;
i.e. it won't have any side effect.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
      a3c751a5
  21. 06 4月, 2020 1 次提交
  23. 02 4月, 2020 14 次提交
    • A
      lookup_open(): don't bother with fallbacks to lookup+create · 99a4a90c
      由 Al Viro 提交于 
      We fall back to lookup+create (instead of atomic_open) in several cases:
	1) we don't have write access to filesystem and O_TRUNC is
present in the flags.  It's not something we want ->atomic_open() to
see - it just might go ahead and truncate the file.  However, we can
pass it the flags sans O_TRUNC - eventually do_open() will call
handle_truncate() anyway.
	2) we have O_CREAT | O_EXCL and we can't write to parent.
That's going to be an error, of course, but we want to know _which_
error should that be - might be EEXIST (if file exists), might be
EACCES or EROFS.  Simply stripping O_CREAT (and checking if we see
ENOENT) would suffice, if not for O_EXCL.  However, we used to have
->atomic_open() fully responsible for rejecting O_CREAT | O_EXCL
on existing file and just stripping O_CREAT would've disarmed
those checks.  With nothing downstream to catch the problem -
FMODE_OPENED used to be "don't bother with EEXIST checks,
->atomic_open() has done those".  Now EEXIST checks downstream
are skipped only if FMODE_CREATED is set - FMODE_OPENED alone
is not enough.  That has eliminated the need to fall back onto
lookup+create path in this case.
	3) O_WRONLY or O_RDWR when we have no write access to
filesystem, with nothing else objectionable.  Fallback is
(and had always been) pointless.

IOW, we don't really need that fallback; all we need in such
cases is to trim O_TRUNC and O_CREAT properly.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      99a4a90c
    • A
      atomic_open(): no need to pass struct open_flags anymore · d489cf9a
      由 Al Viro 提交于 
      argument had been unused since 1643b43f (lookup_open(): lift the
"fallback to !O_CREAT" logics from atomic_open()) back in 2016
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      d489cf9a
    • A
      open_last_lookups(): move complete_walk() into do_open() · ff326a32
      由 Al Viro 提交于 
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      ff326a32
    • A
      open_last_lookups(): lift O_EXCL|O_CREAT handling into do_open() · b94e0b32
      由 Al Viro 提交于 
      Currently path_openat() has "EEXIST on O_EXCL|O_CREAT" checks done on one
of the ways out of open_last_lookups().  There are 4 cases:
	1) the last component is . or ..; check is not done.
	2) we had FMODE_OPENED or FMODE_CREATED set while in lookup_open();
check is not done.
	3) symlink to be traversed is found; check is not done (nor
should it be)
	4) everything else: check done (before complete_walk(), even).

In case (1) O_EXCL|O_CREAT ends up failing with -EISDIR - that's
	open("/tmp/.", O_CREAT|O_EXCL, 0600)
Note that in the same conditions
	open("/tmp", O_CREAT|O_EXCL, 0600)
would have yielded EEXIST.  Either error is allowed, switching to -EEXIST
in these cases would've been more consistent.

Case (2) is more subtle; first of all, if we have FMODE_CREATED set, the
object hadn't existed prior to the call.  The check should not be done in
such a case.  The rest is problematic, though - we have
	FMODE_OPENED set (i.e. it went through ->atomic_open() and got
successfully opened there)
	FMODE_CREATED is *NOT* set
	O_CREAT and O_EXCL are both set.
Any such case is a bug - either we failed to set FMODE_CREATED when we
had, in fact, created an object (no such instances in the tree) or
we have opened a pre-existing file despite having had both O_CREAT and
O_EXCL passed.  One of those was, in fact caught (and fixed) while
sorting out this mess (gfs2 on cold dcache).  And in such situations
we should fail with EEXIST.

Note that for (1) and (4) FMODE_CREATED is not set - for (1) there's nothing
in handle_dots() to set it, for (4) we'd explicitly checked that.

And (1), (2) and (4) are exactly the cases when we leave the loop in
the caller, with do_open() called immediately after that loop.  IOW, we
can move the check over there, and make it

	If we have O_CREAT|O_EXCL and after successful pathname resolution
FMODE_CREATED is *not* set, we must have run into a preexisting file and
should fail with EEXIST.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      b94e0b32
    • A
      open_last_lookups(): don't abuse complete_walk() when all we want is unlazy · 72287417
      由 Al Viro 提交于 
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      72287417
    • A
      open_last_lookups(): consolidate fsnotify_create() calls · f7bb959d
      由 Al Viro 提交于 
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      f7bb959d
    • A
      take post-lookup part of do_last() out of loop · c5971b8c
      由 Al Viro 提交于 
      now we can have open_last_lookups() directly from the loop in
path_openat() - the rest of do_last() never returns a symlink
to follow, so we can bloody well leave the loop first.

Rename the rest of that thing from do_last() to do_open() and
make it return an int.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      c5971b8c
    • A
      link_path_walk(): sample parent's i_uid and i_mode for the last component · 0f705953
      由 Al Viro 提交于 
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      0f705953
    • A
      __nd_alloc_stack(): make it return bool · 60ef60c7
      由 Al Viro 提交于 
      ... and adjust the caller (reserve_stack()).  Rename to nd_alloc_stack(),
while we are at it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      60ef60c7
    • A
      reserve_stack(): switch to __nd_alloc_stack() · 4542576b
      由 Al Viro 提交于 
      expand the call of nd_alloc_stack() into it (and don't
recheck the depth on the second call)
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      4542576b
    • A
      pick_link(): take reserving space on stack into a new helper · 49055906
      由 Al Viro 提交于 
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      49055906
    • A
      pick_link(): more straightforward handling of allocation failures · aef9404d
      由 Al Viro 提交于 
      pick_link() needs to push onto stack; we start with using two-element
array embedded into struct nameidata and the first time we need
more than that we switch to separately allocated array.

Allocation can fail, of course, and handling of that would be simple
enough - we need to drop 'link' and bugger off.  However, the things
get more complicated in RCU mode.  There we must do GFP_ATOMIC
allocation.  If that fails, we try to switch to non-RCU mode and
repeat the allocation.

To switch to non-RCU mode we need to grab references to 'link' and
to everything in nameidata.  The latter done by unlazy_walk();
the former - legitimize_path().  'link' must go first - after
unlazy_walk() we are out of RCU-critical period and it's too
late to call legitimize_path() since the references in link->mnt
and link->dentry might be pointing to freed and reused memory.

So we do legitimize_path(), then unlazy_walk().  And that's where
it gets too subtle: what to do if the former fails?  We MUST
do path_put(link) to avoid leaks.  And we can't do that under
rcu_read_lock().  Solution in mainline was to empty then nameidata
manually, drop out of RCU mode and then do put_path().

In effect, we open-code the things eventual terminate_walk()
would've done on error in RCU mode.  That looks badly out of place
and confusing.  We could add a comment along the lines of the
explanation above, but... there's a simpler solution.  Call
unlazy_walk() even if legitimaze_path() fails.  It will take
us out of RCU mode, so we'll be able to do path_put(link).

Yes, it will do unnecessary work - attempt to grab references
on the stuff in nameidata, only to have them dropped as soon
as we return the error to upper layer and get terminate_walk()
called there.  So what?  We are thoroughly off the fast path
by that point - we had GFP_ATOMIC allocation fail, we had
->d_seq or mount_lock mismatch and we are about to try walking
the same path from scratch in non-RCU mode.  Which will need
to do the same allocation, this time with GFP_KERNEL, so it will
be able to apply memory pressure for blocking stuff.

Compared to that the cost of several lockref_get_not_dead()
is noise.  And the logics become much easier to understand
that way.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      aef9404d
    • A
      fold path_to_nameidata() into its only remaining caller · c99687a0
      由 Al Viro 提交于 
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      c99687a0
    • A
      pick_link(): pass it struct path already with normal refcounting rules · 84f0cd9e
      由 Al Viro 提交于 
      step_into() tries to avoid grabbing and dropping mount references
on the steps that do not involve crossing mountpoints (which is
obviously the majority of cases).  So it uses a local struct path
with unusual refcounting rules - path.mnt is pinned if and only if
it's not equal to nd->path.mnt.

We used to have similar beasts all over the place and we had quite
a few bugs crop up in their handling - it's easy to get confused
when changing e.g. cleanup on failure exits (or adding a new check,
etc.)

Now that's mostly gone - the step_into() instance (which is what
we need them for) is the only one left.  It is exposed to mount
traversal and it's (shortly) seen by pick_link().  Since pick_link()
needs to store it in link stack, where the normal rules apply,
it has to make sure that mount is pinned regardless of nd->path.mnt
value.  That's done on all calls of pick_link() and very early
in those.  Let's do that in the caller (step_into()) instead -
that way the fewer places need to be aware of such struct path
instances.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      84f0cd9e