ext4: add validity checks for bitmap block numbers

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

2 files changed, 21 insertions, 2 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index f82c4966f4ce..a33d8fb1bf2a 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -338,20 +338,25 @@ 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 + sbi->s_itb_per_group),
                         EXT4_B2C(sbi, offset));
@@ -417,6 +422,7 @@ 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;
@@ -425,6 +431,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
         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 - "
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 3fa93665b4a3..df92e3ec9913 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -122,6 +122,7 @@ 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;
@@ -131,6 +132,12 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
                 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 - "