ext4: Fix softlockup caused by illegal i_file_acl value in on-disk inode

If the block containing external extended attributes (which is stored
in i_file_acl and i_file_acl_high) is larger than the on-disk
filesystem, the process which tried to access the extended attributes
will endlessly issue kernel printks complaining that
"__find_get_block_slow() failed", locking up that CPU until the system
is forcibly rebooted.

So when we read in the inode, make sure the i_file_acl value is legal,
and if not, flag the filesystem as being corrupted.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -4409,7 +4409,17 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 			(__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
 	}
 
-	if (ei->i_flags & EXT4_EXTENTS_FL) {
+	if (ei->i_file_acl &&
+	    ((ei->i_file_acl < 
+	      (le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) +
+	       EXT4_SB(sb)->s_gdb_count)) ||
+	     (ei->i_file_acl >= ext4_blocks_count(EXT4_SB(sb)->s_es)))) {
+		ext4_error(sb, __func__,
+			   "bad extended attribute block %llu in inode #%lu",
+			   ei->i_file_acl, inode->i_ino);
+		ret = -EIO;
+		goto bad_inode;
+	} else if (ei->i_flags & EXT4_EXTENTS_FL) {
 		/* Validate extent which is part of inode */
 		ret = ext4_ext_check_inode(inode);
  	} else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||