[PATCH 5.8 070/148] fat: fix fat_ra_init() for data clusters == 0

Greg Kroah-Hartman
2020-08-24T08:34:58Z

From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

[ Upstream commit a090a5a7d73f79a9ae2dcc6e60d89bfc6864a65a ]

If data clusters == 0, fat_ra_init() calls the ->ent_blocknr() for the
cluster beyond ->max_clusters.

This checks the limit before initialization to suppress the warning.

Reported-by: syzbot+756199124937b31a9b7e@syzkaller.appspotmail.com
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/87mu462sv4.fsf@mail.parknet.co.jp
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/fat/fatent.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index bbfe18c074179..f7e3304b78029 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -657,6 +657,9 @@ static void fat_ra_init(struct super_block *sb, struct fatent_ra *ra,
unsigned long ra_pages = sb->s_bdi->ra_pages;
unsigned int reada_blocks;

+ if (fatent->entry >= ent_limit)
+ return;
+
if (ra_pages > sb->s_bdi->io_pages)
ra_pages = rounddown(ra_pages, sb->s_bdi->io_pages);
reada_blocks = ra_pages << (PAGE_SHIFT - sb->s_blocksize_bits + 1);
--
2.25.1