>From bc27e20fdd29b97b45015e1443128b4d3ff9455e Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
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 <jack@suse.cz>
---
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