4.9-stable review patch. If anyone has any objections, please let me know.
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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 @@ -238,6 +238,14 @@ 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, @@ -246,6 +254,12 @@ 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 @@ -1594,6 +1594,8 @@ retry: */ obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
+ pipe_buf_mark_unmergeable(obuf); + obuf->len = len; opipe->nrbufs++; ibuf->offset += obuf->len; @@ -1668,6 +1670,8 @@ 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;