quota: Sanity-check quota file headers on load

Perform basic sanity checks of quota headers to avoid kernel crashes on
corrupted quota files.

CC: stable@vger.kernel.org
Reported-by: syzbot+f816042a7ae2225f25ba@syzkaller.appspotmail.com
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/quota_v2.c

@@ -157,6 +157,25 @@ static int v2_read_file_info(struct super_block *sb, int type)
 		qinfo->dqi_entry_size = sizeof(struct v2r1_disk_dqblk);
 		qinfo->dqi_ops = &v2r1_qtree_ops;
 	}
+	ret = -EUCLEAN;
+	/* Some sanity checks of the read headers... */
+	if ((loff_t)qinfo->dqi_blocks << qinfo->dqi_blocksize_bits >
+	    i_size_read(sb_dqopt(sb)->files[type])) {
+		quota_error(sb, "Number of blocks too big for quota file size (%llu > %llu).",
+		    (loff_t)qinfo->dqi_blocks << qinfo->dqi_blocksize_bits,
+		    i_size_read(sb_dqopt(sb)->files[type]));
+		goto out;
+	}
+	if (qinfo->dqi_free_blk >= qinfo->dqi_blocks) {
+		quota_error(sb, "Free block number too big (%u >= %u).",
+			    qinfo->dqi_free_blk, qinfo->dqi_blocks);
+		goto out;
+	}
+	if (qinfo->dqi_free_entry >= qinfo->dqi_blocks) {
+		quota_error(sb, "Block with free entry too big (%u >= %u).",
+			    qinfo->dqi_free_entry, qinfo->dqi_blocks);
+		goto out;
+	}
 	ret = 0;
 out:
 	up_read(&dqopt->dqio_sem);