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Commit 5b9554dc authored Jul 05, 2016 by Theodore Ts'o

ext4: validate s_reserved_gdt_blocks on mount



If s_reserved_gdt_blocks is extremely large, it's possible for
ext4_init_block_bitmap(), which is called when ext4 sets up an
uninitialized block bitmap, to corrupt random kernel memory.  Add the
same checks which e2fsck has --- it must never be larger than
blocksize / sizeof(__u32) --- and then add a backup check in
ext4_init_block_bitmap() in case the superblock gets modified after
the file system is mounted.

Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

parent de9e9181

fs/ext4/balloc.c

+3 −0

Original line number	Original line	Diff line number	Diff line
	@@ -208,6 +208,9 @@ static int ext4_init_block_bitmap(struct super_block *sb,
	memset(bh->b_data, 0, sb->s_blocksize);		memset(bh->b_data, 0, sb->s_blocksize);

	bit_max = ext4_num_base_meta_clusters(sb, block_group);		bit_max = ext4_num_base_meta_clusters(sb, block_group);
			if ((bit_max >> 3) >= bh->b_size)
			return -EFSCORRUPTED;

	for (bit = 0; bit < bit_max; bit++)		for (bit = 0; bit < bit_max; bit++)
	ext4_set_bit(bit, bh->b_data);		ext4_set_bit(bit, bh->b_data);

fs/ext4/super.c

+7 −0

Original line number	Original line	Diff line number	Diff line
	@@ -3416,6 +3416,13 @@ static int ext4_fill_super(struct super_block sb, void data, int silent)
	goto failed_mount;		goto failed_mount;
	}		}

			if (le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) > (blocksize / 4)) {
			ext4_msg(sb, KERN_ERR,
			"Number of reserved GDT blocks insanely large: %d",
			le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks));
			goto failed_mount;
			}

	if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {		if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
	err = bdev_dax_supported(sb, blocksize);		err = bdev_dax_supported(sb, blocksize);
	if (err)		if (err)