The patch titled
Subject: pipe: cap initial pipe capacity according to pipe-max-size limit
has been added to the -mm tree. Its filename is
pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit.patch
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From: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx>
Subject: 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.
Patch history:
v2
* Switch order of tests in an 'if' statement to avoid a function
call (to capability()) in normal path. [Thanks to Willy Tarreau]
Link: http://lkml.kernel.org/r/31dc7064-2a17-9c5b-1df1-4e3012ee992c@xxxxxxxxx
Signed-off-by: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Cc: Willy Tarreau <w@xxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: <socketpair@xxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/pipe.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN fs/pipe.c~pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit fs/pipe.c
--- a/fs/pipe.c~pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit
+++ a/fs/pipe.c
@@ -631,6 +631,9 @@ struct pipe_inode_info *alloc_pipe_info(
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)) {
_
Patches currently in -mm which might be from mtk.manpages@xxxxxxxxx are
pipe-relocate-round_pipe_size-above-pipe_set_size.patch
pipe-move-limit-checking-logic-into-pipe_set_size.patch
pipe-refactor-argument-for-account_pipe_buffers.patch
pipe-fix-limit-checking-in-pipe_set_size.patch
pipe-simplify-logic-in-alloc_pipe_info.patch
pipe-fix-limit-checking-in-alloc_pipe_info.patch
pipe-make-account_pipe_buffers-return-a-value-and-use-it.patch
pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit.patch
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