>From bc27e20fdd29b97b45015e1443128b4d3ff9455e Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 16 Dec 2019 11:44:14 +0100 Subject: [PATCH] pipe: Fix bogus dereference in iov_iter_alignment() We cannot look at 'i->pipe' unless we know the iter is a pipe. Move the ring_size load to a branch in iov_iter_alignment() where we've already checked the iter is a pipe to avoid bogus dereference. Reported-by: syzbot+bea68382bae9490e7dd6@syzkaller.appspotmail.com Fixes: 8cefc107ca54 ("pipe: Use head and tail pointers for the ring, not cursor and length") Signed-off-by: Jan Kara --- lib/iov_iter.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Al, David, not sure who's going to merge this so sending to both :). Honza diff --git a/lib/iov_iter.c b/lib/iov_iter.c index fb29c02c6a3c..51595bf3af85 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1222,11 +1222,12 @@ EXPORT_SYMBOL(iov_iter_discard); unsigned long iov_iter_alignment(const struct iov_iter *i) { - unsigned int p_mask = i->pipe->ring_size - 1; unsigned long res = 0; size_t size = i->count; if (unlikely(iov_iter_is_pipe(i))) { + unsigned int p_mask = i->pipe->ring_size - 1; + if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask])) return size | i->iov_offset; return size; -- 2.16.4