fat: add simple validation for directory inode

This detects simple corruption cases of directory, and tries to avoid further damage to user data. And performance impact of this validation should be very low, or not measurable. Signed-off-by: OGAWA Hirofumi <[email protected]> Reported-by: Vegard Nossum <[email protected]> Tested-by: Vegard Nossum <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
LeeHayun · Jan 21, 2016 · a3082d5 · a3082d5
1 parent a513d86
commit a3082d5
Showing 1 changed file with 22 additions and 0 deletions.
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
@@ -449,6 +449,24 @@ static int fat_calc_dir_size(struct inode *inode)
 	return 0;
 }
 
+static int fat_validate_dir(struct inode *dir)
+{
+	struct super_block *sb = dir->i_sb;
+
+	if (dir->i_nlink < 2) {
+		/* Directory should have "."/".." entries at least. */
+		fat_fs_error(sb, "corrupted directory (invalid entries)");
+		return -EIO;
+	}
+	if (MSDOS_I(dir)->i_start == 0 ||
+	    MSDOS_I(dir)->i_start == MSDOS_SB(sb)->root_cluster) {
+		/* Directory should point valid cluster. */
+		fat_fs_error(sb, "corrupted directory (invalid i_start)");
+		return -EIO;
+	}
+	return 0;
+}
+
 /* doesn't deal with root inode */
 int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
 {
@@ -475,6 +493,10 @@ int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
 		MSDOS_I(inode)->mmu_private = inode->i_size;
 
 		set_nlink(inode, fat_subdirs(inode));
+
+		error = fat_validate_dir(inode);
+		if (error < 0)
+			return error;
 	} else { /* not a directory */
 		inode->i_generation |= 1;
 		inode->i_mode = fat_make_mode(sbi, de->attr,