releases/4.4.133/pipe-cap-initial-pipe-capacity-according-to-pipe-max-size-limit.patch

   1 From 086e774a57fba4695f14383c0818994c0b31da7c Mon Sep 17 00:00:00 2001
   2 From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
   3 Date: Tue, 11 Oct 2016 13:53:43 -0700
   4 Subject: pipe: cap initial pipe capacity according to pipe-max-size limit
   5
   6 From: Michael Kerrisk (man-pages) <mtk.manpages@gmail.com>
   7
   8 commit 086e774a57fba4695f14383c0818994c0b31da7c upstream.
   9
  10 This is a patch that provides behavior that is more consistent, and
  11 probably less surprising to users. I consider the change optional, and
  12 welcome opinions about whether it should be applied.
  13
  14 By default, pipes are created with a capacity of 64 kiB.  However,
  15 /proc/sys/fs/pipe-max-size may be set smaller than this value.  In this
  16 scenario, an unprivileged user could thus create a pipe whose initial
  17 capacity exceeds the limit. Therefore, it seems logical to cap the
  18 initial pipe capacity according to the value of pipe-max-size.
  19
  20 The test program shown earlier in this patch series can be used to
  21 demonstrate the effect of the change brought about with this patch:
  22
  23     # cat /proc/sys/fs/pipe-max-size
  24     1048576
  25     # sudo -u mtk ./test_F_SETPIPE_SZ 1
  26     Initial pipe capacity: 65536
  27     # echo 10000 > /proc/sys/fs/pipe-max-size
  28     # cat /proc/sys/fs/pipe-max-size
  29     16384
  30     # sudo -u mtk ./test_F_SETPIPE_SZ 1
  31     Initial pipe capacity: 16384
  32     # ./test_F_SETPIPE_SZ 1
  33     Initial pipe capacity: 65536
  34
  35 The last two executions of 'test_F_SETPIPE_SZ' show that pipe-max-size
  36 caps the initial allocation for a new pipe for unprivileged users, but
  37 not for privileged users.
  38
  39 Link: http://lkml.kernel.org/r/31dc7064-2a17-9c5b-1df1-4e3012ee992c@gmail.com
  40 Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
  41 Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
  42 Cc: Willy Tarreau <w@1wt.eu>
  43 Cc: <socketpair@gmail.com>
  44 Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
  45 Cc: Jens Axboe <axboe@fb.com>
  46 Cc: Al Viro <viro@zeniv.linux.org.uk>
  47 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  48 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  49 Signed-off-by: Daniel Sangorrin <daniel.sangorrin@toshiba.co.jp>
  50 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  51
  52 ---
  53  fs/pipe.c |    3 +++
  54  1 file changed, 3 insertions(+)
  55
  56 --- a/fs/pipe.c
  57 +++ b/fs/pipe.c
  58 @@ -616,6 +616,9 @@ struct pipe_inode_info *alloc_pipe_info(
  59                 unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
  60                 struct user_struct *user = get_current_user();
  61
  62 +               if (pipe_bufs * PAGE_SIZE > pipe_max_size && !capable(CAP_SYS_RESOURCE))
  63 +                       pipe_bufs = pipe_max_size >> PAGE_SHIFT;
  64 +
  65                 if (!too_many_pipe_buffers_hard(user)) {
  66                         if (too_many_pipe_buffers_soft(user))
  67                                 pipe_bufs = 1;