On Sun, 2018-04-22 at 15:53 +0200, Greg Kroah-Hartman wrote: > 4.9-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Theodore Ts'o <tytso@xxxxxxx> > > 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@xxxxxxxxxx> > Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > --- > fs/ext4/balloc.c | 16 ++++++++++++++-- > fs/ext4/ialloc.c | 7 +++++++ > 2 files changed, 21 insertions(+), 2 deletions(-) > > --- a/fs/ext4/balloc.c > +++ b/fs/ext4/balloc.c > @@ -337,20 +337,25 @@ static ext4_fsblk_t ext4_valid_block_bit > /* 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)) Isn't sb->s_blocksize a count of bytes? If so, doesn't that mean that we should be comparing with sb->s_blocksize * 8? Ben. > /* 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 + EXT4_SB(sb)->s_itb_per_group), > EXT4_B2C(sbi, offset)); > @@ -416,6 +421,7 @@ 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; > @@ -424,6 +430,12 @@ ext4_read_block_bitmap_nowait(struct sup > 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 - " > --- a/fs/ext4/ialloc.c > +++ b/fs/ext4/ialloc.c > @@ -119,6 +119,7 @@ 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; > @@ -128,6 +129,12 @@ ext4_read_inode_bitmap(struct super_bloc > 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 - " > > -- Ben Hutchings It is easier to write an incorrect program than to understand a correct one.
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