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authorMichael Kerrisk (man-pages) <mtk.manpages@gmail.com>2016-10-11 13:53:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-10-11 15:06:32 -0700
commit086e774a57fba4695f14383c0818994c0b31da7c (patch)
treec8c9ced5e9fca1f95ba2caedd08278da10fa3aae
parent9c87bcf0a31b338dc8a69a5d251a037565a94e13 (diff)
pipe: cap initial pipe capacity according to pipe-max-size limit
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>
-rw-r--r--fs/pipe.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/pipe.c b/fs/pipe.c
index 5ff02c4afe9f..8e0d9f26dfad 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -628,6 +628,9 @@ struct pipe_inode_info *alloc_pipe_info(void)
if (pipe == NULL)
goto out_free_uid;
+ if (pipe_bufs * PAGE_SIZE > pipe_max_size && !capable(CAP_SYS_RESOURCE))
+ pipe_bufs = pipe_max_size >> PAGE_SHIFT;
+
user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
if (too_many_pipe_buffers_soft(user_bufs)) {