From: "Michael Kerrisk (man-pages)" mtk.manpages@gmail.com

[ Upstream commit 086e774a57fba4695f14383c0818994c0b31da7c]

This is a patch that provides behavior that is more consistent, and probably less surprising to users. I consider the change optional, and welcome opinions about whether it should be applied.

By default, pipes are created with a capacity of 64 kiB. However, /proc/sys/fs/pipe-max-size may be set smaller than this value. In this scenario, an unprivileged user could thus create a pipe whose initial capacity exceeds the limit. Therefore, it seems logical to cap the initial pipe capacity according to the value of pipe-max-size.

The test program shown earlier in this patch series can be used to demonstrate the effect of the change brought about with this patch:

# cat /proc/sys/fs/pipe-max-size 1048576 # sudo -u mtk ./test_F_SETPIPE_SZ 1 Initial pipe capacity: 65536 # echo 10000 > /proc/sys/fs/pipe-max-size # cat /proc/sys/fs/pipe-max-size 16384 # sudo -u mtk ./test_F_SETPIPE_SZ 1 Initial pipe capacity: 16384 # ./test_F_SETPIPE_SZ 1 Initial pipe capacity: 65536

The last two executions of 'test_F_SETPIPE_SZ' show that pipe-max-size caps the initial allocation for a new pipe for unprivileged users, but not for privileged users.

Link: http://lkml.kernel.org/r/31dc7064-2a17-9c5b-1df1-4e3012ee992c@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: Daniel Sangorrin daniel.sangorrin@toshiba.co.jp (Backported from commit 086e774a57fba4695f14383c0818994c0b31da7c) --- fs/pipe.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/fs/pipe.c b/fs/pipe.c index 39eff9a..1e7263b 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -616,6 +616,9 @@ struct pipe_inode_info *alloc_pipe_info(void) unsigned long pipe_bufs = PIPE_DEF_BUFFERS; struct user_struct *user = get_current_user();

+ if (pipe_bufs * PAGE_SIZE > pipe_max_size && !capable(CAP_SYS_RESOURCE)) + pipe_bufs = pipe_max_size >> PAGE_SHIFT; + if (!too_many_pipe_buffers_hard(user)) { if (too_many_pipe_buffers_soft(user)) pipe_bufs = 1;