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 f491bd71118beba608d39ac2d5f1530e1160cd2e upstream.
Patch series "pipe: fix limit handling", v2.
When changing a pipe's capacity with fcntl(F_SETPIPE_SZ), various limits defined by /proc/sys/fs/pipe-* files are checked to see if unprivileged users are exceeding limits on memory consumption.
While documenting and testing the operation of these limits I noticed that, as currently implemented, these checks have a number of problems:
(1) When increasing the pipe capacity, the checks against the limits in /proc/sys/fs/pipe-user-pages-{soft,hard} are made against existing consumption, and exclude the memory required for the increased pipe capacity. The new increase in pipe capacity can then push the total memory used by the user for pipes (possibly far) over a limit. This can also trigger the problem described next.
(2) The limit checks are performed even when the new pipe capacity is less than the existing pipe capacity. This can lead to problems if a user sets a large pipe capacity, and then the limits are lowered, with the result that the user will no longer be able to decrease the pipe capacity.
(3) 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 series addresses these three problems.
This patch (of 8):
This is a minor preparatory patch. After subsequent patches, round_pipe_size() will be called from pipe_set_size(), so place round_pipe_size() above pipe_set_size().
Link: http://lkml.kernel.org/r/91a91fdb-a959-ba7f-b551-b62477cc98a1@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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/pipe.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-)
--- a/fs/pipe.c +++ b/fs/pipe.c @@ -994,6 +994,18 @@ const struct file_operations pipefifo_fo };
/* + * Currently we rely on the pipe array holding a power-of-2 number + * of pages. + */ +static inline unsigned int round_pipe_size(unsigned int size) +{ + unsigned long nr_pages; + + nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; + return roundup_pow_of_two(nr_pages) << PAGE_SHIFT; +} + +/* * Allocate a new array of pipe buffers and copy the info over. Returns the * pipe size if successful, or return -ERROR on error. */ @@ -1044,18 +1056,6 @@ static long pipe_set_size(struct pipe_in }
/* - * Currently we rely on the pipe array holding a power-of-2 number - * of pages. - */ -static inline unsigned int round_pipe_size(unsigned int size) -{ - unsigned long nr_pages; - - nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; - return roundup_pow_of_two(nr_pages) << PAGE_SHIFT; -} - -/* * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax * will return an error. */