add-bitmap-block-validity-checks

   1 ext4: add validity checks for bitmap block numbers
   2
   3 An privileged attacker can cause a crash by mounting a crafted ext4
   4 image which triggers a out-of-bounds read in the function
   5 ext4_valid_block_bitmap() in fs/ext4/balloc.c.
   6
   7 This issue has been assigned CVE-2018-1093.
   8
   9 BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=199181
  10 BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1560782
  11 Reported-by: Wen Xu <wen.xu@gatech.edu>
  12 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  13 Cc: stable@vger.kernel.org
  14 ---
  15  fs/ext4/balloc.c | 16 ++++++++++++++--
  16  fs/ext4/ialloc.c |  7 +++++++
  17  2 files changed, 21 insertions(+), 2 deletions(-)
  18
  19 diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
  20 index f82c4966f4ce..a33d8fb1bf2a 100644
  21 --- a/fs/ext4/balloc.c
  22 +++ b/fs/ext4/balloc.c
  23 @@ -338,20 +338,25 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb,
  24         /* check whether block bitmap block number is set */
  25         blk = ext4_block_bitmap(sb, desc);
  26         offset = blk - group_first_block;
  27 -       if (!ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
  28 +       if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
  29 +           !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
  30                 /* bad block bitmap */
  31                 return blk;
  32
  33         /* check whether the inode bitmap block number is set */
  34         blk = ext4_inode_bitmap(sb, desc);
  35         offset = blk - group_first_block;
  36 -       if (!ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
  37 +       if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
  38 +           !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
  39                 /* bad block bitmap */
  40                 return blk;
  41
  42         /* check whether the inode table block number is set */
  43         blk = ext4_inode_table(sb, desc);
  44         offset = blk - group_first_block;
  45 +       if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
  46 +           EXT4_B2C(sbi, offset + sbi->s_itb_per_group) >= sb->s_blocksize)
  47 +               return blk;
  48         next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
  49                         EXT4_B2C(sbi, offset + sbi->s_itb_per_group),
  50                         EXT4_B2C(sbi, offset));
  51 @@ -417,6 +422,7 @@ struct buffer_head *
  52  ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
  53  {
  54         struct ext4_group_desc *desc;
  55 +       struct ext4_sb_info *sbi = EXT4_SB(sb);
  56         struct buffer_head *bh;
  57         ext4_fsblk_t bitmap_blk;
  58         int err;
  59 @@ -425,6 +431,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
  60         if (!desc)
  61                 return ERR_PTR(-EFSCORRUPTED);
  62         bitmap_blk = ext4_block_bitmap(sb, desc);
  63 +       if ((bitmap_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
  64 +           (bitmap_blk >= ext4_blocks_count(sbi->s_es))) {
  65 +               ext4_error(sb, "Invalid block bitmap block %llu in "
  66 +                          "block_group %u", bitmap_blk, block_group);
  67 +               return ERR_PTR(-EFSCORRUPTED);
  68 +       }
  69         bh = sb_getblk(sb, bitmap_blk);
  70         if (unlikely(!bh)) {
  71                 ext4_error(sb, "Cannot get buffer for block bitmap - "
  72 diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
  73 index 3fa93665b4a3..df92e3ec9913 100644
  74 --- a/fs/ext4/ialloc.c
  75 +++ b/fs/ext4/ialloc.c
  76 @@ -122,6 +122,7 @@ static struct buffer_head *
  77  ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
  78  {
  79         struct ext4_group_desc *desc;
  80 +       struct ext4_sb_info *sbi = EXT4_SB(sb);
  81         struct buffer_head *bh = NULL;
  82         ext4_fsblk_t bitmap_blk;
  83         int err;
  84 @@ -131,6 +132,12 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
  85                 return ERR_PTR(-EFSCORRUPTED);
  86
  87         bitmap_blk = ext4_inode_bitmap(sb, desc);
  88 +       if ((bitmap_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
  89 +           (bitmap_blk >= ext4_blocks_count(sbi->s_es))) {
  90 +               ext4_error(sb, "Invalid inode bitmap blk %llu in "
  91 +                          "block_group %u", bitmap_blk, block_group);
  92 +               return ERR_PTR(-EFSCORRUPTED);
  93 +       }
  94         bh = sb_getblk(sb, bitmap_blk);
  95         if (unlikely(!bh)) {
  96                 ext4_error(sb, "Cannot read inode bitmap - "