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
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 3fa9366..df92e3e 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 - "