From 943ebf4d8c50dcbd474483b023955f4716e0c5bb Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 23 Jan 2019 15:19:17 +0100 Subject: 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(). Cc: Fixes: 7c77f0b3f920 ("splice: implement pipe to pipe splicing") Fixes: 70524490ee2e ("[PATCH] splice: add support for sys_tee()") Suggested-by: Al Viro Signed-off-by: Jann Horn Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/splice.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs/splice.c') diff --git a/fs/splice.c b/fs/splice.c index 8dd79ecfd383..01983bea760c 100644 --- 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_info *ipipe, */ obuf->flags &= ~PIPE_BUF_FLAG_GIFT; + pipe_buf_mark_unmergeable(obuf); + if (obuf->len > len) obuf->len = len; -- cgit v1.2.3