avoid-arithmetic-overflow-that-can-trigger-a-BUG

   1 ext4: avoid arithemetic overflow that can trigger a BUG
   2
   3 A maliciously crafted file system can cause an overflow when the
   4 results of a 64-bit calculation is stored into a 32-bit length
   5 parameter.
   6
   7 https://bugzilla.kernel.org/show_bug.cgi?id=200623
   8
   9 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  10 Reported-by: Wen Xu <wen.xu@gatech.edu>
  11 Cc: stable@vger.kernel.org
  12 ---
  13  fs/ext4/ext4.h  | 3 +++
  14  fs/ext4/inode.c | 8 ++++++--
  15  2 files changed, 9 insertions(+), 2 deletions(-)
  16
  17 diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
  18 index 249bcee4d7b2..ac05bd86643a 100644
  19 --- a/fs/ext4/ext4.h
  20 +++ b/fs/ext4/ext4.h
  21 @@ -686,6 +686,9 @@ enum {
  22  /* Max physical block we can address w/o extents */
  23  #define EXT4_MAX_BLOCK_FILE_PHYS       0xFFFFFFFF
  24
  25 +/* Max logical block we can support */
  26 +#define EXT4_MAX_LOGICAL_BLOCK         0xFFFFFFFF
  27 +
  28  /*
  29   * Structure of an inode on the disk
  30   */
  31 diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
  32 index 8f6ad7667974..694f31364206 100644
  33 --- a/fs/ext4/inode.c
  34 +++ b/fs/ext4/inode.c
  35 @@ -3412,12 +3412,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
  36  {
  37         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
  38         unsigned int blkbits = inode->i_blkbits;
  39 -       unsigned long first_block = offset >> blkbits;
  40 -       unsigned long last_block = (offset + length - 1) >> blkbits;
  41 +       unsigned long first_block, last_block;
  42         struct ext4_map_blocks map;
  43         bool delalloc = false;
  44         int ret;
  45
  46 +       if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
  47 +               return -EINVAL;
  48 +       first_block = offset >> blkbits;
  49 +       last_block = min_t(loff_t, (offset + length - 1) >> blkbits,
  50 +                          EXT4_MAX_LOGICAL_BLOCK);
  51
  52         if (flags & IOMAP_REPORT) {
  53                 if (ext4_has_inline_data(inode)) {