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Subject[PATCH 5.0 087/238] splice: dont merge into linked buffers
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jannh@google.com>

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().

Cc: <stable@vger.kernel.org>
Fixes: 7c77f0b3f920 ("splice: implement pipe to pipe splicing")
Fixes: 70524490ee2e ("[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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/pipe.c | 14 ++++++++++++++
fs/splice.c | 4 ++++
include/linux/pipe_fs_i.h | 1 +
3 files changed, 19 insertions(+)

--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -234,6 +234,14 @@ static const struct pipe_buf_operations
.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
.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)
{
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -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_i
*/
obuf->flags &= ~PIPE_BUF_FLAG_GIFT;

+ pipe_buf_mark_unmergeable(obuf);
+
if (obuf->len > len)
obuf->len = len;

--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -182,6 +182,7 @@ void generic_pipe_buf_get(struct pipe_in
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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