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  1. 30 1月, 2016 1 次提交
  3. 25 11月, 2015 1 次提交
  5. 23 7月, 2015 1 次提交
  7. 17 4月, 2015 1 次提交
    • M
      fork: report pid reservation failure properly · 35f71bc0
      由 Michal Hocko 提交于 
      copy_process will report any failure in alloc_pid as ENOMEM currently
which is misleading because the pid allocation might fail not only when
the memory is short but also when the pid space is consumed already.

The current man page even mentions this case:

: EAGAIN
:
:       A system-imposed limit on the number of threads was encountered.
:       There are a number of limits that may trigger this error: the
:       RLIMIT_NPROC soft resource limit (set via setrlimit(2)), which
:       limits the number of processes and threads for a real user ID, was
:       reached; the kernel's system-wide limit on the number of processes
:       and threads, /proc/sys/kernel/threads-max, was reached (see
:       proc(5)); or the maximum number of PIDs, /proc/sys/kernel/pid_max,
:       was reached (see proc(5)).

so the current behavior is also incorrect wrt.  documentation.  POSIX man
page also suggest returing EAGAIN when the process count limit is reached.

This patch simply propagates error code from alloc_pid and makes sure we
return -EAGAIN due to reservation failure.  This will make behavior of
fork closer to both our documentation and POSIX.

alloc_pid might alsoo fail when the reaper in the pid namespace is dead
(the namespace basically disallows all new processes) and there is no
good error code which would match documented ones. We have traditionally
returned ENOMEM for this case which is misleading as well but as per
Eric W. Biederman this behavior is documented in man pid_namespaces(7)

: If the "init" process of a PID namespace terminates, the kernel
: terminates all of the processes in the namespace via a SIGKILL signal.
: This behavior reflects the fact that the "init" process is essential for
: the correct operation of a PID namespace.  In this case, a subsequent
: fork(2) into this PID namespace will fail with the error ENOMEM; it is
: not possible to create a new processes in a PID namespace whose "init"
: process has terminated.

and introducing a new error code would be too risky so let's stick to
ENOMEM for this case.
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      35f71bc0
  9. 11 12月, 2014 1 次提交
  11. 05 12月, 2014 2 次提交
  13. 01 10月, 2013 1 次提交
  15. 31 8月, 2013 1 次提交
    • E
      pidns: Fix hang in zap_pid_ns_processes by sending a potentially extra wakeup · a6064885
      由 Eric W. Biederman 提交于 
      Serge Hallyn <serge.hallyn@ubuntu.com> writes:

> Since commit af4b8a83 it's been
> possible to get into a situation where a pidns reaper is
> <defunct>, reparented to host pid 1, but never reaped.  How to
> reproduce this is documented at
>
> https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1168526
> (and see
> https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1168526/comments/13)
> In short, run repeated starts of a container whose init is
>
> Process.exit(0);
>
> sysrq-t when such a task is playing zombie shows:
>
> [  131.132978] init            x ffff88011fc14580     0  2084   2039 0x00000000
> [  131.132978]  ffff880116e89ea8 0000000000000002 ffff880116e89fd8 0000000000014580
> [  131.132978]  ffff880116e89fd8 0000000000014580 ffff8801172a0000 ffff8801172a0000
> [  131.132978]  ffff8801172a0630 ffff88011729fff0 ffff880116e14650 ffff88011729fff0
> [  131.132978] Call Trace:
> [  131.132978]  [<ffffffff816f6159>] schedule+0x29/0x70
> [  131.132978]  [<ffffffff81064591>] do_exit+0x6e1/0xa40
> [  131.132978]  [<ffffffff81071eae>] ? signal_wake_up_state+0x1e/0x30
> [  131.132978]  [<ffffffff8106496f>] do_group_exit+0x3f/0xa0
> [  131.132978]  [<ffffffff810649e4>] SyS_exit_group+0x14/0x20
> [  131.132978]  [<ffffffff8170102f>] tracesys+0xe1/0xe6
>
> Further debugging showed that every time this happened, zap_pid_ns_processes()
> started with nr_hashed being 3, while we were expecting it to drop to 2.
> Any time it didn't happen, nr_hashed was 1 or 2.  So the reaper was
> waiting for nr_hashed to become 2, but free_pid() only wakes the reaper
> if nr_hashed hits 1.

The issue is that when the task group leader of an init process exits
before other tasks of the init process when the init process finally
exits it will be a secondary task sleeping in zap_pid_ns_processes and
waiting to wake up when the number of hashed pids drops to two.  This
case waits forever as free_pid only sends a wake up when the number of
hashed pids drops to 1.

To correct this the simple strategy of sending a possibly unncessary
wake up when the number of hashed pids drops to 2 is adopted.

Sending one extraneous wake up is relatively harmless, at worst we
waste a little cpu time in the rare case when a pid namespace
appropaches exiting.

We can detect the case when the pid namespace drops to just two pids
hashed race free in free_pid.

Dereferencing pid_ns->child_reaper with the pidmap_lock held is safe
without out the tasklist_lock because it is guaranteed that the
detach_pid will be called on the child_reaper before it is freed and
detach_pid calls __change_pid which calls free_pid which takes the
pidmap_lock.  __change_pid only calls free_pid if this is the
last use of the pid.  For a thread that is not the thread group leader
the threads pid will only ever have one user because a threads pid
is not allowed to be the pid of a process, of a process group or
a session.  For a thread that is a thread group leader all of
the other threads of that process will be reaped before it is allowed
for the thread group leader to be reaped ensuring there will only
be one user of the threads pid as a process pid.  Furthermore
because the thread is the init process of a pid namespace all of the
other processes in the pid namespace will have also been already freed
leading to the fact that the pid will not be used as a session pid or
a process group pid for any other running process.

CC: stable@vger.kernel.org
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Tested-by: NSerge Hallyn <serge.hallyn@canonical.com>
Reported-by: NSerge Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      a6064885
  17. 04 7月, 2013 2 次提交
  19. 02 5月, 2013 1 次提交
  21. 01 5月, 2013 2 次提交
  23. 28 2月, 2013 1 次提交
    • S
      hlist: drop the node parameter from iterators · b67bfe0d
      由 Sasha Levin 提交于 
      I'm not sure why, but the hlist for each entry iterators were conceived

        list_for_each_entry(pos, head, member)

The hlist ones were greedy and wanted an extra parameter:

        hlist_for_each_entry(tpos, pos, head, member)

Why did they need an extra pos parameter? I'm not quite sure. Not only
they don't really need it, it also prevents the iterator from looking
exactly like the list iterator, which is unfortunate.

Besides the semantic patch, there was some manual work required:

 - Fix up the actual hlist iterators in linux/list.h
 - Fix up the declaration of other iterators based on the hlist ones.
 - A very small amount of places were using the 'node' parameter, this
 was modified to use 'obj->member' instead.
 - Coccinelle didn't handle the hlist_for_each_entry_safe iterator
 properly, so those had to be fixed up manually.

The semantic patch which is mostly the work of Peter Senna Tschudin is here:

@@
iterator name hlist_for_each_entry, hlist_for_each_entry_continue, hlist_for_each_entry_from, hlist_for_each_entry_rcu, hlist_for_each_entry_rcu_bh, hlist_for_each_entry_continue_rcu_bh, for_each_busy_worker, ax25_uid_for_each, ax25_for_each, inet_bind_bucket_for_each, sctp_for_each_hentry, sk_for_each, sk_for_each_rcu, sk_for_each_from, sk_for_each_safe, sk_for_each_bound, hlist_for_each_entry_safe, hlist_for_each_entry_continue_rcu, nr_neigh_for_each, nr_neigh_for_each_safe, nr_node_for_each, nr_node_for_each_safe, for_each_gfn_indirect_valid_sp, for_each_gfn_sp, for_each_host;

type T;
expression a,c,d,e;
identifier b;
statement S;
@@

-T b;
    <+... when != b
(
hlist_for_each_entry(a,
- b,
c, d) S
|
hlist_for_each_entry_continue(a,
- b,
c) S
|
hlist_for_each_entry_from(a,
- b,
c) S
|
hlist_for_each_entry_rcu(a,
- b,
c, d) S
|
hlist_for_each_entry_rcu_bh(a,
- b,
c, d) S
|
hlist_for_each_entry_continue_rcu_bh(a,
- b,
c) S
|
for_each_busy_worker(a, c,
- b,
d) S
|
ax25_uid_for_each(a,
- b,
c) S
|
ax25_for_each(a,
- b,
c) S
|
inet_bind_bucket_for_each(a,
- b,
c) S
|
sctp_for_each_hentry(a,
- b,
c) S
|
sk_for_each(a,
- b,
c) S
|
sk_for_each_rcu(a,
- b,
c) S
|
sk_for_each_from
-(a, b)
+(a)
S
+ sk_for_each_from(a) S
|
sk_for_each_safe(a,
- b,
c, d) S
|
sk_for_each_bound(a,
- b,
c) S
|
hlist_for_each_entry_safe(a,
- b,
c, d, e) S
|
hlist_for_each_entry_continue_rcu(a,
- b,
c) S
|
nr_neigh_for_each(a,
- b,
c) S
|
nr_neigh_for_each_safe(a,
- b,
c, d) S
|
nr_node_for_each(a,
- b,
c) S
|
nr_node_for_each_safe(a,
- b,
c, d) S
|
- for_each_gfn_sp(a, c, d, b) S
+ for_each_gfn_sp(a, c, d) S
|
- for_each_gfn_indirect_valid_sp(a, c, d, b) S
+ for_each_gfn_indirect_valid_sp(a, c, d) S
|
for_each_host(a,
- b,
c) S
|
for_each_host_safe(a,
- b,
c, d) S
|
for_each_mesh_entry(a,
- b,
c, d) S
)
    ...+>

[akpm@linux-foundation.org: drop bogus change from net/ipv4/raw.c]
[akpm@linux-foundation.org: drop bogus hunk from net/ipv6/raw.c]
[akpm@linux-foundation.org: checkpatch fixes]
[akpm@linux-foundation.org: fix warnings]
[akpm@linux-foudnation.org: redo intrusive kvm changes]
Tested-by: NPeter Senna Tschudin <peter.senna@gmail.com>
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NSasha Levin <sasha.levin@oracle.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      b67bfe0d
  25. 13 2月, 2013 1 次提交
  27. 26 12月, 2012 1 次提交
    • E
      pidns: Stop pid allocation when init dies · c876ad76
      由 Eric W. Biederman 提交于 
      Oleg pointed out that in a pid namespace the sequence.
- pid 1 becomes a zombie
- setns(thepidns), fork,...
- reaping pid 1.
- The injected processes exiting.

Can lead to processes attempting access their child reaper and
instead following a stale pointer.

That waitpid for init can return before all of the processes in
the pid namespace have exited is also unfortunate.

Avoid these problems by disabling the allocation of new pids in a pid
namespace when init dies, instead of when the last process in a pid
namespace is reaped.
Pointed-out-by: NOleg Nesterov <oleg@redhat.com>
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      c876ad76
  29. 18 12月, 2012 1 次提交
  31. 06 12月, 2012 1 次提交
  33. 20 11月, 2012 1 次提交
    • E
      proc: Usable inode numbers for the namespace file descriptors. · 98f842e6
      由 Eric W. Biederman 提交于 
      Assign a unique proc inode to each namespace, and use that
inode number to ensure we only allocate at most one proc
inode for every namespace in proc.

A single proc inode per namespace allows userspace to test
to see if two processes are in the same namespace.

This has been a long requested feature and only blocked because
a naive implementation would put the id in a global space and
would ultimately require having a namespace for the names of
namespaces, making migration and certain virtualization tricks
impossible.

We still don't have per superblock inode numbers for proc, which
appears necessary for application unaware checkpoint/restart and
migrations (if the application is using namespace file descriptors)
but that is now allowd by the design if it becomes important.

I have preallocated the ipc and uts initial proc inode numbers so
their structures can be statically initialized.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
      98f842e6
  35. 19 11月, 2012 5 次提交
    • E
      pidns: Wait in zap_pid_ns_processes until pid_ns->nr_hashed == 1 · af4b8a83
      由 Eric W. Biederman 提交于 
      Looking at pid_ns->nr_hashed is a bit simpler and it works for
disjoint process trees that an unshare or a join of a pid_namespace
may create.
Acked-by: N"Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      af4b8a83
    • E
      pidns: Don't allow new processes in a dead pid namespace. · 5e1182de
      由 Eric W. Biederman 提交于 
      Set nr_hashed to -1 just before we schedule the work to cleanup proc.
Test nr_hashed just before we hash a new pid and if nr_hashed is < 0
fail.

This guaranteees that processes never enter a pid namespaces after we
have cleaned up the state to support processes in a pid namespace.

Currently sending SIGKILL to all of the process in a pid namespace as
init exists gives us this guarantee but we need something a little
stronger to support unsharing and joining a pid namespace.
Acked-by: N"Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
      5e1182de
    • E
      pidns: Make the pidns proc mount/umount logic obvious. · 0a01f2cc
      由 Eric W. Biederman 提交于 
      Track the number of pids in the proc hash table.  When the number of
pids goes to 0 schedule work to unmount the kernel mount of proc.

Move the mount of proc into alloc_pid when we allocate the pid for
init.

Remove the surprising calls of pid_ns_release proc in fork and
proc_flush_task.  Those code paths really shouldn't know about proc
namespace implementation details and people have demonstrated several
times that finding and understanding those code paths is difficult and
non-obvious.

Because of the call path detach pid is alwasy called with the
rtnl_lock held free_pid is not allowed to sleep, so the work to
unmounting proc is moved to a work queue.  This has the side benefit
of not blocking the entire world waiting for the unnecessary
rcu_barrier in deactivate_locked_super.

In the process of making the code clear and obvious this fixes a bug
reported by Gao feng <gaofeng@cn.fujitsu.com> where we would leak a
mount of proc during clone(CLONE_NEWPID|CLONE_NEWNET) if copy_pid_ns
succeeded and copy_net_ns failed.
Acked-by: N"Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      0a01f2cc
    • E
      pidns: Use task_active_pid_ns where appropriate · 17cf22c3
      由 Eric W. Biederman 提交于 
      The expressions tsk->nsproxy->pid_ns and task_active_pid_ns
aka ns_of_pid(task_pid(tsk)) should have the same number of
cache line misses with the practical difference that
ns_of_pid(task_pid(tsk)) is released later in a processes life.

Furthermore by using task_active_pid_ns it becomes trivial
to write an unshare implementation for the the pid namespace.

So I have used task_active_pid_ns everywhere I can.

In fork since the pid has not yet been attached to the
process I use ns_of_pid, to achieve the same effect.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
      17cf22c3
    • E
      pidns: Capture the user namespace and filter ns_last_pid · 49f4d8b9
      由 Eric W. Biederman 提交于 
      - Capture the the user namespace that creates the pid namespace
- Use that user namespace to test if it is ok to write to
  /proc/sys/kernel/ns_last_pid.

Zhao Hongjiang <zhaohongjiang@huawei.com> noticed I was missing a put_user_ns
in when destroying a pid_ns.  I have foloded his patch into this one
so that bisects will work properly.
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      49f4d8b9
  37. 15 8月, 2012 1 次提交
    • E
      net ip6 flowlabel: Make owner a union of struct pid * and kuid_t · 4f82f457
      由 Eric W. Biederman 提交于 
      Correct a long standing omission and use struct pid in the owner
field of struct ip6_flowlabel when the share type is IPV6_FL_S_PROCESS.
This guarantees we don't have issues when pid wraparound occurs.

Use a kuid_t in the owner field of struct ip6_flowlabel when the
share type is IPV6_FL_S_USER to add user namespace support.

In /proc/net/ip6_flowlabel capture the current pid namespace when
opening the file and release the pid namespace when the file is
closed ensuring we print the pid owner value that is meaning to
the reader of the file.  Similarly use from_kuid_munged to print
uid values that are meaningful to the reader of the file.

This requires exporting pid_nr_ns so that ipv6 can continue to built
as a module.  Yoiks what silliness
Acked-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
      4f82f457
  39. 24 5月, 2012 1 次提交
  41. 14 2月, 2012 1 次提交
  43. 13 1月, 2012 1 次提交
  45. 31 10月, 2011 1 次提交
  47. 29 9月, 2011 1 次提交
    • P
      rcu: Restore checks for blocking in RCU read-side critical sections · b3fbab05
      由 Paul E. McKenney 提交于 
      Long ago, using TREE_RCU with PREEMPT would result in "scheduling
while atomic" diagnostics if you blocked in an RCU read-side critical
section.  However, PREEMPT now implies TREE_PREEMPT_RCU, which defeats
this diagnostic.  This commit therefore adds a replacement diagnostic
based on PROVE_RCU.

Because rcu_lockdep_assert() and lockdep_rcu_dereference() are now being
used for things that have nothing to do with rcu_dereference(), rename
lockdep_rcu_dereference() to lockdep_rcu_suspicious() and add a third
argument that is a string indicating what is suspicious.  This third
argument is passed in from a new third argument to rcu_lockdep_assert().
Update all calls to rcu_lockdep_assert() to add an informative third
argument.

Also, add a pair of rcu_lockdep_assert() calls from within
rcu_note_context_switch(), one complaining if a context switch occurs
in an RCU-bh read-side critical section and another complaining if a
context switch occurs in an RCU-sched read-side critical section.
These are present only if the PROVE_RCU kernel parameter is enabled.

Finally, fix some checkpatch whitespace complaints in lockdep.c.

Again, you must enable PROVE_RCU to see these new diagnostics.  But you
are enabling PROVE_RCU to check out new RCU uses in any case, aren't you?
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      b3fbab05
  49. 09 7月, 2011 1 次提交
  51. 19 4月, 2011 1 次提交
    • L
      next_pidmap: fix overflow condition · c78193e9
      由 Linus Torvalds 提交于 
      next_pidmap() just quietly accepted whatever 'last' pid that was passed
in, which is not all that safe when one of the users is /proc.

Admittedly the proc code should do some sanity checking on the range
(and that will be the next commit), but that doesn't mean that the
helper functions should just do that pidmap pointer arithmetic without
checking the range of its arguments.

So clamp 'last' to PID_MAX_LIMIT.  The fact that we then do "last+1"
doesn't really matter, the for-loop does check against the end of the
pidmap array properly (it's only the actual pointer arithmetic overflow
case we need to worry about, and going one bit beyond isn't going to
overflow).

[ Use PID_MAX_LIMIT rather than pid_max as per Eric Biederman ]
Reported-by: NTavis Ormandy <taviso@cmpxchg8b.com>
Analyzed-by: NRobert Święcki <robert@swiecki.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c78193e9
  53. 18 3月, 2011 1 次提交
  55. 20 8月, 2010 2 次提交
    • T
      Add RCU check for find_task_by_vpid(). · 4221a991
      由 Tetsuo Handa 提交于 
      find_task_by_vpid() says "Must be called under rcu_read_lock().". But due to
commit 3120438a "rcu: Disable lockdep checking in RCU list-traversal primitives",
we are currently unable to catch "find_task_by_vpid() with tasklist_lock held
but RCU lock not held" errors due to the RCU-lockdep checks being
suppressed in the RCU variants of the struct list_head traversals.
This commit therefore places an explicit check for being in an RCU
read-side critical section in find_task_by_pid_ns().

  ===================================================
  [ INFO: suspicious rcu_dereference_check() usage. ]
  ---------------------------------------------------
  kernel/pid.c:386 invoked rcu_dereference_check() without protection!

  other info that might help us debug this:

  rcu_scheduler_active = 1, debug_locks = 1
  1 lock held by rc.sysinit/1102:
   #0:  (tasklist_lock){.+.+..}, at: [<c1048340>] sys_setpgid+0x40/0x160

  stack backtrace:
  Pid: 1102, comm: rc.sysinit Not tainted 2.6.35-rc3-dirty #1
  Call Trace:
   [<c105e714>] lockdep_rcu_dereference+0x94/0xb0
   [<c104b4cd>] find_task_by_pid_ns+0x6d/0x70
   [<c104b4e8>] find_task_by_vpid+0x18/0x20
   [<c1048347>] sys_setpgid+0x47/0x160
   [<c1002b50>] sysenter_do_call+0x12/0x36

Commit updated to use a new rcu_lockdep_assert() exported API rather than
the old internal __do_rcu_dereference().
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
      4221a991
    • A
      rculist: avoid __rcu annotations · 67bdbffd
      由 Arnd Bergmann 提交于 
      This avoids warnings from missing __rcu annotations
in the rculist implementation, making it possible to
use the same lists in both RCU and non-RCU cases.

We can add rculist annotations later, together with
lockdep support for rculist, which is missing as well,
but that may involve changing all the users.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
      67bdbffd
  57. 11 8月, 2010 2 次提交
    • O
      pids: alloc_pidmap: remove the unnecessary boundary checks · c52b0b91
      由 Oleg Nesterov 提交于 
      alloc_pidmap() calculates max_scan so that if the initial offset != 0 we
inspect the first map->page twice.  This is correct, we want to find the
unused bits < offset in this bitmap block.  Add the comment.

But it doesn't make any sense to stop the find_next_offset() loop when we
are looking into this map->page for the second time.  We have already
already checked the bits >= offset during the first attempt, it is fine to
do this again, no matter if we succeed this time or not.

Remove this hard-to-understand code.  It optimizes the very unlikely case
when we are going to fail, but slows down the more likely case.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Cc: Salman Qazi <sqazi@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c52b0b91
    • S
      pids: fix a race in pid generation that causes pids to be reused immediately · 5fdee8c4
      由 Salman 提交于 
      A program that repeatedly forks and waits is susceptible to having the
same pid repeated, especially when it competes with another instance of
the same program.  This is really bad for bash implementation.
Furthermore, many shell scripts assume that pid numbers will not be used
for some length of time.

Race Description:

A                                    B

// pid == offset == n                // pid == offset == n + 1
test_and_set_bit(offset, map->page)
                                     test_and_set_bit(offset, map->page);
                                     pid_ns->last_pid = pid;
pid_ns->last_pid = pid;
                                     // pid == n + 1 is freed (wait())

                                     // Next fork()...
                                     last = pid_ns->last_pid; // == n
                                     pid = last + 1;

Code to reproduce it (Running multiple instances is more effective):

#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

// The distance mod 32768 between two pids, where the first pid is expected
// to be smaller than the second.
int PidDistance(pid_t first, pid_t second) {
  return (second + 32768 - first) % 32768;
}

int main(int argc, char* argv[]) {
  int failed = 0;
  pid_t last_pid = 0;
  int i;
  printf("%d\n", sizeof(pid_t));
  for (i = 0; i < 10000000; ++i) {
    if (i % 32786 == 0)
      printf("Iter: %d\n", i/32768);
    int child_exit_code = i % 256;
    pid_t pid = fork();
    if (pid == -1) {
      fprintf(stderr, "fork failed, iteration %d, errno=%d", i, errno);
      exit(1);
    }
    if (pid == 0) {
      // Child
      exit(child_exit_code);
    } else {
      // Parent
      if (i > 0) {
        int distance = PidDistance(last_pid, pid);
        if (distance == 0 || distance > 30000) {
          fprintf(stderr,
                  "Unexpected pid sequence: previous fork: pid=%d, "
                  "current fork: pid=%d for iteration=%d.\n",
                  last_pid, pid, i);
          failed = 1;
        }
      }
      last_pid = pid;
      int status;
      int reaped = wait(&status);
      if (reaped != pid) {
        fprintf(stderr,
                "Wait return value: expected pid=%d, "
                "got %d, iteration %d\n",
                pid, reaped, i);
        failed = 1;
      } else if (WEXITSTATUS(status) != child_exit_code) {
        fprintf(stderr,
                "Unexpected exit status %x, iteration %d\n",
                WEXITSTATUS(status), i);
        failed = 1;
      }
    }
  }
  exit(failed);
}

Thanks to Ted Tso for the key ideas of this implementation.
Signed-off-by: NSalman Qazi <sqazi@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5fdee8c4
  59. 28 5月, 2010 1 次提交
  61. 07 3月, 2010 1 次提交