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Commit f8d4d52c authored by Theodore Ts'o's avatar Theodore Ts'o Committed by Greg Kroah-Hartman
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ext4: validate s_reserved_gdt_blocks on mount 



commit 5b9554dc5bf008ae7f68a52e3d7e76c0920938a2 upstream.

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: default avatarVegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 175f36cb

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
@@ -3372,6 +3372,13 @@ 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) {

		if (blocksize != PAGE_SIZE) {

			ext4_msg(sb, KERN_ERR,