linux-kernel - [PATCH AUTOSEL 5.8 26/27] fat: fix fat_ra

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Message-Id: <20200820000116.214821-26-sashal@kernel.org>
Date:   Wed, 19 Aug 2020 20:01:15 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        syzbot+756199124937b31a9b7e@...kaller.appspotmail.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.8 26/27] fat: fix fat_ra_init() for data clusters == 0

From: OGAWA Hirofumi <hirofumi@...l.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@...kaller.appspotmail.com
Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Link: http://lkml.kernel.org/r/87mu462sv4.fsf@mail.parknet.co.jp
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.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