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
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 5664ee6..13c49af7 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3416,6 +3416,13 @@
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)