[PATCH 1/3] ext4: add validity checks for bitmap block numbers

[Harsh Shandilya <harsh@prjkt.io>]

From: Theodore Ts'o <tytso@mit.edu>

Commit 7dac4a1726a9c64a517d595c40e95e2d0d135f6f upstream.

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.

Backport notes:
3.18.y is missing commit 6a797d273783 ("ext4: call out CRC and corruption errors with specific error codes")
so the EFSCORRUPTED label doesn't exist. Replaced
all instances of EFSCORRUPTED with EUCLEAN since that's
what 6a797d273783 defined it as.

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
[harsh@prjkt.io: s/EFSCORRUPTED/EUCLEAN/ fs/ext4/balloc.c]
Signed-off-by: Harsh Shandilya <harsh@prjkt.io>
---
 fs/ext4/balloc.c | 16 ++++++++++++++--
 fs/ext4/ialloc.c |  8 +++++++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index cb3860817fed..3b88f0ca0e82 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -340,20 +340,25 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb,
 	/* 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;
 
@@ -423,6 +429,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	if (!desc)
 		return NULL;
 	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(-EUCLEAN);
+	}
 	bh = sb_getblk(sb, bitmap_blk);
 	if (unlikely(!bh)) {
 		ext4_error(sb, "Cannot get buffer for block bitmap - "
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index b7d49d2ab74f..9595daf6a44f 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -123,16 +123,22 @@ 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;
 	struct ext4_group_info *grp;
-	struct ext4_sb_info *sbi = EXT4_SB(sb);
 
 	desc = ext4_get_group_desc(sb, block_group, NULL);
 	if (!desc)
 		return NULL;
 
 	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(-EUCLEAN);
+	}
 	bh = sb_getblk(sb, bitmap_blk);
 	if (unlikely(!bh)) {
 		ext4_error(sb, "Cannot read inode bitmap - "
-- 
2.15.0.2308.g658a28aa74af