fat: fix fat_ra_init() for data clusters == 0

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>

diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index bbfe18c..f7e3304 100644 (file)
--- 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);