From 7dac4a1726a9c64a517d595c40e95e2d0d135f6f Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Mon, 26 Mar 2018 23:54:10 -0400
Subject: [PATCH] ext4: add validity checks for bitmap block numbers
Git-commit: 7dac4a1726a9c64a517d595c40e95e2d0d135f6f
Patch-mainline: v4.17-rc1
References: bsc#1087095 cve-2018-1093

An privileged attacker can cause a crash by mounting a crafted ext4
image which triggers a out-of-bounds read in the function
ext4_valid_block_bitmap() in fs/ext4/balloc.c.

This issue has been assigned CVE-2018-1093.

Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=199181
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1560782
Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/ext4/balloc.c |   16 ++++++++++++++--
 fs/ext4/ialloc.c |    7 +++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -337,20 +337,25 @@ static ext4_fsblk_t ext4_valid_block_bit
 	/* check whether block bitmap block number is set */
 	blk = ext4_block_bitmap(sb, desc);
 	offset = blk - group_first_block;
-	if (!ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
+	if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
+	    !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
 		/* bad block bitmap */
 		return blk;
 
 	/* check whether the inode bitmap block number is set */
 	blk = ext4_inode_bitmap(sb, desc);
 	offset = blk - group_first_block;
-	if (!ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
+	if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
+	    !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
 		/* bad block bitmap */
 		return blk;
 
 	/* check whether the inode table block number is set */
 	blk = ext4_inode_table(sb, desc);
 	offset = blk - group_first_block;
+	if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
+	    EXT4_B2C(sbi, offset + sbi->s_itb_per_group) >= sb->s_blocksize)
+		return blk;
 	next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
 			EXT4_B2C(sbi, offset + EXT4_SB(sb)->s_itb_per_group),
 			EXT4_B2C(sbi, offset));
@@ -416,6 +421,7 @@ struct buffer_head *
 ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 {
 	struct ext4_group_desc *desc;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct buffer_head *bh;
 	ext4_fsblk_t bitmap_blk;
 	int err;
@@ -424,6 +430,12 @@ ext4_read_block_bitmap_nowait(struct sup
 	if (!desc)
 		return ERR_PTR(-EFSCORRUPTED);
 	bitmap_blk = ext4_block_bitmap(sb, desc);
+	if ((bitmap_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
+	    (bitmap_blk >= ext4_blocks_count(sbi->s_es))) {
+		ext4_error(sb, "Invalid block bitmap block %llu in "
+			   "block_group %u", bitmap_blk, block_group);
+		return ERR_PTR(-EFSCORRUPTED);
+	}
 	bh = sb_getblk(sb, bitmap_blk);
 	if (unlikely(!bh)) {
 		ext4_error(sb, "Cannot get buffer for block bitmap - "
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -121,6 +121,7 @@ static struct buffer_head *
 ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
 {
 	struct ext4_group_desc *desc;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct buffer_head *bh = NULL;
 	ext4_fsblk_t bitmap_blk;
 	int err;
@@ -130,6 +131,12 @@ ext4_read_inode_bitmap(struct super_bloc
 		return ERR_PTR(-EFSCORRUPTED);
 
 	bitmap_blk = ext4_inode_bitmap(sb, desc);
+	if ((bitmap_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
+	    (bitmap_blk >= ext4_blocks_count(sbi->s_es))) {
+		ext4_error(sb, "Invalid inode bitmap blk %llu in "
+			   "block_group %u", bitmap_blk, block_group);
+		return ERR_PTR(-EFSCORRUPTED);
+	}
 	bh = sb_getblk(sb, bitmap_blk);
 	if (unlikely(!bh)) {
 		ext4_error(sb, "Cannot read inode bitmap - "