3.16.57-rc1 review patch. If anyone has any objections, please let me know.
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From: "Michael Kerrisk (man-pages)" mtk.manpages@gmail.com
commit a005ca0e6813e1d796a7422a7e31d8b8d6555df1 upstream.
The limit checking in alloc_pipe_info() (used by pipe(2) and when opening a FIFO) has the following problems:
(1) When checking capacity required for the new pipe, the checks against the limit in /proc/sys/fs/pipe-user-pages-{soft,hard} are made against existing consumption, and exclude the memory required for the new pipe capacity. As a consequence: (1) the memory allocation throttling provided by the soft limit does not kick in quite as early as it should, and (2) the user can overrun the hard limit.
(2) As currently implemented, accounting and checking against the limits is done as follows:
(a) Test whether the user has exceeded the limit. (b) Make new pipe buffer allocation. (c) Account new allocation against the limits.
This is racey. Multiple processes may pass point (a) simultaneously, and then allocate pipe buffers that are accounted for only in step (c). The race means that the user's pipe buffer allocation could be pushed over the limit (by an arbitrary amount, depending on how unlucky we were in the race). [Thanks to Vegard Nossum for spotting this point, which I had missed.]
This patch addresses the above problems as follows:
* Alter the checks against limits to include the memory required for the new pipe. * Re-order the accounting step so that it precedes the buffer allocation. If the accounting step determines that a limit has been reached, revert the accounting and cause the operation to fail.
Link: http://lkml.kernel.org/r/8ff3e9f9-23f6-510c-644f-8e70cd1c0bd9@gmail.com Signed-off-by: Michael Kerrisk mtk.manpages@gmail.com Reviewed-by: Vegard Nossum vegard.nossum@oracle.com Cc: Willy Tarreau w@1wt.eu Cc: socketpair@gmail.com Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: Jens Axboe axboe@fb.com Cc: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [bwh: Backported to 3.16: Don't use GFP_KERNEL_ACCOUNT] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/pipe.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)
--- a/fs/pipe.c +++ b/fs/pipe.c @@ -618,24 +618,30 @@ struct pipe_inode_info *alloc_pipe_info( if (pipe == NULL) goto out_free_uid;
- if (!too_many_pipe_buffers_hard(user)) { - if (too_many_pipe_buffers_soft(user)) - pipe_bufs = 1; - pipe->bufs = kcalloc(pipe_bufs, - sizeof(struct pipe_buffer), - GFP_KERNEL); + account_pipe_buffers(user, 0, pipe_bufs); + + if (too_many_pipe_buffers_soft(user)) { + account_pipe_buffers(user, pipe_bufs, 1); + pipe_bufs = 1; }
+ if (too_many_pipe_buffers_hard(user)) + goto out_revert_acct; + + pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer), + GFP_KERNEL); + if (pipe->bufs) { init_waitqueue_head(&pipe->wait); pipe->r_counter = pipe->w_counter = 1; pipe->buffers = pipe_bufs; pipe->user = user; - account_pipe_buffers(user, 0, pipe_bufs); mutex_init(&pipe->mutex); return pipe; }
+out_revert_acct: + account_pipe_buffers(user, pipe_bufs, 0); kfree(pipe); out_free_uid: free_uid(user);