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splice: don't merge into linked buffers 

commit a0ce2f0aa6ad97c3d4927bf2ca54bcebdf062d55 upstream.

Before this patch, it was possible for two pipes to affect each other after
data had been transferred between them with tee():

============
$ cat tee_test.c

int main(void) {
  int pipe_a[2];
  if (pipe(pipe_a)) err(1, "pipe");
  int pipe_b[2];
  if (pipe(pipe_b)) err(1, "pipe");
  if (write(pipe_a[1], "abcd", 4) != 4) err(1, "write");
  if (tee(pipe_a[0], pipe_b[1], 2, 0) != 2) err(1, "tee");
  if (write(pipe_b[1], "xx", 2) != 2) err(1, "write");

  char buf[5];
  if (read(pipe_a[0], buf, 4) != 4) err(1, "read");
  buf[4] = 0;
  printf("got back: '%s'\n", buf);
}
$ gcc -o tee_test tee_test.c
$ ./tee_test
got back: 'abxx'
$
============

As suggested by Al Viro, fix it by creating a separate type for
non-mergeable pipe buffers, then changing the types of buffers in
splice_pipe_to_pipe() and link_pipe().

Fixes: 7c77f0b3f9 ("splice: implement pipe to pipe splicing")
Fixes: 70524490ee ("[PATCH] splice: add support for sys_tee()")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.16: Use generic_pipe_buf_steal(), as for other pipe
 types, since anon_pipe_buf_steal() does not exist here]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Jann Horn 2019-01-23 15:19:17 +01:00 committed by syphyr
parent 32be75b125
commit f716247d29
3 changed files with 19 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
fs/pipe.c
View File

@ -364,6 +364,14 @@ static const struct pipe_buf_operations anon_pipe_buf_ops = {
.get = generic_pipe_buf_get,
};
static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
.can_merge = 0,
.confirm = generic_pipe_buf_confirm,
.release = anon_pipe_buf_release,
.steal = generic_pipe_buf_steal,
.get = generic_pipe_buf_get,
};
static const struct pipe_buf_operations packet_pipe_buf_ops = {
.can_merge = 0,
.map = generic_pipe_buf_map,
@ -374,6 +382,12 @@ static const struct pipe_buf_operations packet_pipe_buf_ops = {
.get = generic_pipe_buf_get,
};
void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
{
if (buf->ops == &anon_pipe_buf_ops)
buf->ops = &anon_pipe_buf_nomerge_ops;
}
static ssize_t
pipe_read(struct kiocb *iocb, const struct iovec *_iov,
unsigned long nr_segs, loff_t pos)

4
fs/splice.c
View File

@ -1953,6 +1953,8 @@ retry:
*/
obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
pipe_buf_mark_unmergeable(obuf);
obuf->len = len;
opipe->nrbufs++;
ibuf->offset += obuf->len;
@ -2027,6 +2029,8 @@ static int link_pipe(struct pipe_inode_info *ipipe,
*/
obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
pipe_buf_mark_unmergeable(obuf);
if (obuf->len > len)
obuf->len = len;

1
include/linux/pipe_fs_i.h
View File

@ -159,6 +159,7 @@ void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
extern const struct pipe_buf_operations nosteal_pipe_buf_ops;