Commit 5467159c authored Jul 05, 2016 by Theodore Ts'o Committed by Sasha Levin Aug 22, 2016

ext4: validate s_reserved_gdt_blocks on mount



[ Upstream commit e1d8c1feecf672379c50ab045fd94548468bc987 ]

[ Upstream commit 5b9554dc5bf008ae7f68a52e3d7e76c0920938a2 ]

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
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

parent 926d244d

fs/ext4/balloc.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -209,6 +209,9 @@ 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 -EIO;

		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
		@@ -3668,6 +3668,13 @@ 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 (sb->s_blocksize != blocksize) {
		/* Validate the filesystem blocksize */
		if (!sb_set_blocksize(sb, blocksize)) {