From 086e774a57fba4695f14383c0818994c0b31da7c Mon Sep 17 00:00:00 2001 From: "Michael Kerrisk (man-pages)" Date: Tue, 11 Oct 2016 13:53:43 -0700 Subject: [PATCH] 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 Reviewed-by: Vegard Nossum Cc: Willy Tarreau Cc: Cc: Tetsuo Handa Cc: Jens Axboe Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/pipe.c | 3 +++ 1 file changed, 3 insertions(+) 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)) {