ext4: add more inode number paranoia checks

If there is a directory entry pointing to a system inode (such as a
journal inode), complain and declare the file system to be corrupted.

Also, if the superblock's first inode number field is too small,
refuse to mount the file system.

This addresses CVE-2018-10882.

https://bugzilla.kernel.org/show_bug.cgi?id=200069

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

3 files changed, 7 insertions, 6 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 859d6433dcc1..4bd69649a048 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1502,11 +1502,6 @@ static inline struct ext4_inode_info *EXT4_I(struct inode *inode)
 static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 {
         return ino == EXT4_ROOT_INO ||
-                ino == EXT4_USR_QUOTA_INO ||
-                ino == EXT4_GRP_QUOTA_INO ||
-                ino == EXT4_BOOT_LOADER_INO ||
-                ino == EXT4_JOURNAL_INO ||
-                ino == EXT4_RESIZE_INO ||
                 (ino >= EXT4_FIRST_INO(sb) &&
                  ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
 }
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c2f4ccb880c4..7d6c10017bdf 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4506,7 +4506,8 @@ static int __ext4_get_inode_loc(struct inode *inode,
         int                     inodes_per_block, inode_offset;
 
         iloc->bh = NULL;
-        if (!ext4_valid_inum(sb, inode->i_ino))
+        if (inode->i_ino < EXT4_ROOT_INO ||
+            inode->i_ino > le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count))
                 return -EFSCORRUPTED;
 
         iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4d34430d75f6..1f955c128e0d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3858,6 +3858,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
         } else {
                 sbi->s_inode_size = le16_to_cpu(es->s_inode_size);
                 sbi->s_first_ino = le32_to_cpu(es->s_first_ino);
+                if (sbi->s_first_ino < EXT4_GOOD_OLD_FIRST_INO) {
+                        ext4_msg(sb, KERN_ERR, "invalid first ino: %u",
+                                 sbi->s_first_ino);
+                        goto failed_mount;
+                }
                 if ((sbi->s_inode_size < EXT4_GOOD_OLD_INODE_SIZE) ||
                     (!is_power_of_2(sbi->s_inode_size)) ||
                     (sbi->s_inode_size > blocksize)) {