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 <hirofumi@mail.parknet.co.jp>
Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Tested-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 3ac9078fde65f87ef3b434d21af0cb78211f3953..08ef5fd0d5029326430b76f0b28d34d7cd52255f 100644 (file)
--- 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,