3.18-stable review patch. If anyone has any objections, please let me know.
------------------ From: Michael Kerrisk (man-pages) <[email protected]> commit 086e774a57fba4695f14383c0818994c0b31da7c upstream. 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/[email protected] Signed-off-by: Michael Kerrisk <[email protected]> Reviewed-by: Vegard Nossum <[email protected]> Cc: Willy Tarreau <[email protected]> Cc: <[email protected]> Cc: Tetsuo Handa <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Al Viro <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Daniel Sangorrin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- fs/pipe.c | 3 +++ 1 file changed, 3 insertions(+) --- a/fs/pipe.c +++ b/fs/pipe.c @@ -618,6 +618,9 @@ struct pipe_inode_info *alloc_pipe_info( 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;
