linux-ext4 - [Bug 199181] Out-of-bound access in ext4_valid_block_bitmap when mounting and operating on a crafted ext4 image

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Date:   Sat, 24 Mar 2018 06:30:58 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...nel.org
Subject: [Bug 199181] Out-of-bound access in ext4_valid_block_bitmap when
 mounting and operating on a crafted ext4 image

https://bugzilla.kernel.org/show_bug.cgi?id=199181

--- Comment #3 from Theodore Tso (tytso@....edu) ---
Thanks for the bug report.  The following should address the problem
you have reported.

commit 25584a8748b1f5404abcdc87c9fac21681eec5d2
Author: Theodore Ts'o <tytso@....edu>
Date:   Sat Mar 24 01:48:34 2018 -0400

    ext4: add validity checks for bitmap block numbers

    https://bugzilla.kernel.org/show_bug.cgi?id=199181

    Reported-by: Wen Xu <wen.xu@...ech.edu>
    Signed-off-by: Theodore Ts'o <tytso@....edu>
    Cc: stable@...r.kernel.org

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index f82c4966f4ce..a33d8fb1bf2a 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -338,20 +338,25 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct
super_block *sb,
        /* 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))
                /* 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 + sbi->s_itb_per_group),
                        EXT4_B2C(sbi, offset));
@@ -417,6 +422,7 @@ 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;
@@ -425,6 +431,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb,
ext4_group_t block_group)
        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 - "
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 3fa93665b4a3..df92e3ec9913 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 - "

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