ext4: validate s_reserved_gdt_blocks on mount (5b9554dc) · Commits · 戴 / test

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

fs/ext4/balloc.c

+3 −0

Original line number	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);

		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++)
		ext4_set_bit(bit, bh->b_data);

fs/ext4/super.c

+7 −0

Original line number	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;
		}

		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) {
		err = bdev_dax_supported(sb, blocksize);
		if (err)

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