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Subject[PATCH] fat: Don't allow to mount if the FAT length == 0
Date
If FAT length == 0, the image doesn't have any data. And it can be the
cause of overlapping the root dir and FAT entries.

Also Windows treats it as invalid format.

Reported-by: syzbot+6f1624f937d9d6911e2d@syzkaller.appspotmail.com
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---
fs/fat/inode.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 71946da..bf8e04e 100644
--- a/fs/fat/inode.c 2020-04-07 21:55:27.001147223 +0900
+++ b/fs/fat/inode.c 2020-04-07 22:06:15.164098069 +0900
@@ -1520,6 +1520,12 @@ static int fat_read_bpb(struct super_blo
goto out;
}

+ if (bpb->fat_fat_length == 0 && bpb->fat32_length == 0) {
+ if (!silent)
+ fat_msg(sb, KERN_ERR, "bogus number of FAT sectors");
+ goto out;
+ }
+
error = 0;

out:
_
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes:
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