exfat: fix the infinite loop in exfat_find_last_cluster()

[ Upstream commit b0522303f67255926b946aa66885a0104d1b2980 ]

In exfat_find_last_cluster(), the cluster chain is traversed until
the EOF cluster. If the cluster chain includes a loop due to file
system corruption, the EOF cluster cannot be traversed, resulting
in an infinite loop.

If the number of clusters indicated by the file size is inconsistent
with the cluster chain length, exfat_find_last_cluster() will return
an error, so if this inconsistency is found, the traversal can be
aborted without traversing to the EOF cluster.

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=f7d147e6db52b1e09dba
Tested-by: [email protected]
Fixes: 3102386 ("exfat: add fat entry operations")
Signed-off-by: Yuezhang Mo <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: YuezhangMo

fs/exfat/fatent.c

@@ -265,7 +265,7 @@ int exfat_find_last_cluster(struct super_block *sb, struct exfat_chain *p_chain,
 		clu = next;
 		if (exfat_ent_get(sb, clu, &next))
 			return -EIO;
-	} while (next != EXFAT_EOF_CLUSTER);
+	} while (next != EXFAT_EOF_CLUSTER && count <= p_chain->size);
 
 	if (p_chain->size != count) {
 		exfat_fs_error(sb,