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: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index fe1f50fe764ff9238354e2e30491c6e1e6d149b9..f97110461c196b2b770baa7d2e0b7694cb750fa2 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -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);
 

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 852c26806af275a1f3894c0a990c341540f23c06..2d7b5462bcaa29dc25e96c1a9ca9ac1944250ae8 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -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,