[PATCH] fs: fat: add check for dir size in fat_calc_dir_size

[Anupam Aggarwal]

Max directory size of FAT filesystem is FAT_MAX_DIR_SIZE(2097152 bytes)
It is possible that, due to corruption, directory size calculated in
fat_calc_dir_size() can be greater than FAT_MAX_DIR_SIZE, i.e.
can be in GBs, hence directory traversal can take long time.
for example when command "ls -lR" is executed on corrupted FAT
formatted USB, fat_search_long() function will lookup for a filename from
position 0 till end of corrupted directory size, multiple such lookups
will lead to long directory traversal

Added sanity check for directory size fat_calc_dir_size(),
and return EIO error, which will prevent lookup in corrupted directory

Signed-off-by: Anupam Aggarwal <anupam.al@xxxxxxxxxxx>
Signed-off-by: Amit Sahrawat <a.sahrawat@xxxxxxxxxxx>
---
 fs/fat/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index a0cf99d..9b2e81e 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -490,6 +490,13 @@ static int fat_calc_dir_size(struct inode *inode)
 		return ret;
 	inode->i_size = (fclus + 1) << sbi->cluster_bits;
 
+	if (i_size_read(inode) > FAT_MAX_DIR_SIZE) {
+		fat_fs_error(inode->i_sb,
+			     "%s corrupted directory (invalid size %lld)\n",
+			     __func__, i_size_read(inode));
+		return -EIO;
+	}
+
 	return 0;
 }
 
-- 
1.9.1