Commit a0ce2f0a authored by Jann Horn's avatar Jann Horn Committed by Al Viro
Browse files

splice: don't merge into linked buffers 



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().

Cc: <stable@vger.kernel.org>
Fixes: 7c77f0b3 ("splice: implement pipe to pipe splicing")
Fixes: 70524490 ("[PATCH] splice: add support for sys_tee()")
Suggested-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarJann Horn <jannh@google.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 801e5237

fs/pipe.c

+14 −0
Original line number Diff line number Diff line
@@ -234,6 +234,14 @@ 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 = anon_pipe_buf_steal,

	.get = generic_pipe_buf_get,

};



static const struct pipe_buf_operations packet_pipe_buf_ops = {

	.can_merge = 0,

	.confirm = generic_pipe_buf_confirm,
@@ -242,6 +250,12 @@ 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, struct iov_iter *to)

{

fs/splice.c

+4 −0
Original line number Diff line number Diff line
@@ -1597,6 +1597,8 @@ retry: 
			 */

			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;



			pipe_buf_mark_unmergeable(obuf);



			obuf->len = len;

			opipe->nrbufs++;

			ibuf->offset += obuf->len;
@@ -1671,6 +1673,8 @@ 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;

include/linux/pipe_fs_i.h

+1 −0
Original line number Diff line number Diff line
@@ -182,6 +182,7 @@ 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;

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