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ext4: add validity checks for bitmap block numbers

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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
This commit is contained in:
Theodore Ts'o 2018-03-26 23:54:10 -04:00
parent dcae058a8d
commit 7dac4a1726
2 changed files with 21 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

16
fs/ext4/balloc.c
View file

@ -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 - "

7
fs/ext4/ialloc.c
View file

@ -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 - "