ext4: add validity checks for bitmap block numbers

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.

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>
[bwh: Backported to 3.2:
 - In ext4_valid_block_bitmap(), goto err_out on error
 - In ext4_read_{block,inode}_bitmap(), return NULL on error
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index f91de78..fc69043 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -298,20 +298,25 @@ static int ext4_valid_block_bitmap(struct super_block *sb,
        /* check whether block bitmap block number is set */
        bitmap_blk = ext4_block_bitmap(sb, desc);
        offset = bitmap_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 */
                goto err_out;
 
        /* check whether the inode bitmap block number is set */
        bitmap_blk = ext4_inode_bitmap(sb, desc);
        offset = bitmap_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 */
                goto err_out;
 
        /* check whether the inode table block number is set */
        bitmap_blk = ext4_inode_table(sb, desc);
        offset = bitmap_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)
+               goto err_out;
        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));
@@ -339,6 +344,7 @@ struct buffer_head *
 ext4_read_block_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;
 
@@ -346,6 +352,12 @@ ext4_read_block_bitmap(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 NULL;
+       }
        bh = sb_getblk(sb, bitmap_blk);
        if (unlikely(!bh)) {
                ext4_error(sb, "Cannot read block bitmap - "

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 476caae..9603b79 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -102,6 +102,7 @@ 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;
 
@@ -110,6 +111,12 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
                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 NULL;
+       }
        bh = sb_getblk(sb, bitmap_blk);
        if (unlikely(!bh)) {
                ext4_error(sb, "Cannot read inode bitmap - "