releases/4.19.31/splice-don-t-merge-into-linked-buffers.patch

   1 From a0ce2f0aa6ad97c3d4927bf2ca54bcebdf062d55 Mon Sep 17 00:00:00 2001
   2 From: Jann Horn <jannh@google.com>
   3 Date: Wed, 23 Jan 2019 15:19:17 +0100
   4 Subject: splice: don't merge into linked buffers
   5
   6 From: Jann Horn <jannh@google.com>
   7
   8 commit a0ce2f0aa6ad97c3d4927bf2ca54bcebdf062d55 upstream.
   9
  10 Before this patch, it was possible for two pipes to affect each other after
  11 data had been transferred between them with tee():
  12
  13 ============
  14 $ cat tee_test.c
  15
  16 int main(void) {
  17   int pipe_a[2];
  18   if (pipe(pipe_a)) err(1, "pipe");
  19   int pipe_b[2];
  20   if (pipe(pipe_b)) err(1, "pipe");
  21   if (write(pipe_a[1], "abcd", 4) != 4) err(1, "write");
  22   if (tee(pipe_a[0], pipe_b[1], 2, 0) != 2) err(1, "tee");
  23   if (write(pipe_b[1], "xx", 2) != 2) err(1, "write");
  24
  25   char buf[5];
  26   if (read(pipe_a[0], buf, 4) != 4) err(1, "read");
  27   buf[4] = 0;
  28   printf("got back: '%s'\n", buf);
  29 }
  30 $ gcc -o tee_test tee_test.c
  31 $ ./tee_test
  32 got back: 'abxx'
  33 $
  34 ============
  35
  36 As suggested by Al Viro, fix it by creating a separate type for
  37 non-mergeable pipe buffers, then changing the types of buffers in
  38 splice_pipe_to_pipe() and link_pipe().
  39
  40 Cc: <stable@vger.kernel.org>
  41 Fixes: 7c77f0b3f920 ("splice: implement pipe to pipe splicing")
  42 Fixes: 70524490ee2e ("[PATCH] splice: add support for sys_tee()")
  43 Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
  44 Signed-off-by: Jann Horn <jannh@google.com>
  45 Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
  46 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  47
  48 ---
  49  fs/pipe.c                 |   14 ++++++++++++++
  50  fs/splice.c               |    4 ++++
  51  include/linux/pipe_fs_i.h |    1 +
  52  3 files changed, 19 insertions(+)
  53
  54 --- a/fs/pipe.c
  55 +++ b/fs/pipe.c
  56 @@ -234,6 +234,14 @@ static const struct pipe_buf_operations
  57         .get = generic_pipe_buf_get,
  58  };
  59
  60 +static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
  61 +       .can_merge = 0,
  62 +       .confirm = generic_pipe_buf_confirm,
  63 +       .release = anon_pipe_buf_release,
  64 +       .steal = anon_pipe_buf_steal,
  65 +       .get = generic_pipe_buf_get,
  66 +};
  67 +
  68  static const struct pipe_buf_operations packet_pipe_buf_ops = {
  69         .can_merge = 0,
  70         .confirm = generic_pipe_buf_confirm,
  71 @@ -242,6 +250,12 @@ static const struct pipe_buf_operations
  72         .get = generic_pipe_buf_get,
  73  };
  74
  75 +void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
  76 +{
  77 +       if (buf->ops == &anon_pipe_buf_ops)
  78 +               buf->ops = &anon_pipe_buf_nomerge_ops;
  79 +}
  80 +
  81  static ssize_t
  82  pipe_read(struct kiocb *iocb, struct iov_iter *to)
  83  {
  84 --- a/fs/splice.c
  85 +++ b/fs/splice.c
  86 @@ -1593,6 +1593,8 @@ retry:
  87                          */
  88                         obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
  89
  90 +                       pipe_buf_mark_unmergeable(obuf);
  91 +
  92                         obuf->len = len;
  93                         opipe->nrbufs++;
  94                         ibuf->offset += obuf->len;
  95 @@ -1667,6 +1669,8 @@ static int link_pipe(struct pipe_inode_i
  96                  */
  97                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
  98
  99 +               pipe_buf_mark_unmergeable(obuf);
 100 +
 101                 if (obuf->len > len)
 102                         obuf->len = len;
 103
 104 --- a/include/linux/pipe_fs_i.h
 105 +++ b/include/linux/pipe_fs_i.h
 106 @@ -182,6 +182,7 @@ void generic_pipe_buf_get(struct pipe_in
 107  int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
 108  int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 109  void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
 110 +void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
 111
 112  extern const struct pipe_buf_operations nosteal_pipe_buf_ops;
 113