Commit 24b38673 authored by Theodore Ts'o's avatar Theodore Ts'o Committed by Ben Hutchings

ext4: validate s_reserved_gdt_blocks on mount

commit 5b9554dc 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>
[bwh: Backported to 3.16:
 - Use EIO instead of EFSCORRUPTED
 - Adjust context]
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 0180a021
......@@ -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);
......
......@@ -3644,6 +3644,13 @@ 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)) {
......
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