Patch "fs/nilfs2: fix potential underflow in call to crc32_le" has been added to the 4.6-stable tree

This is a note to let you know that I've just added the patch titled

fs/nilfs2: fix potential underflow in call to crc32_le

to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fs-nilfs2-fix-potential-underflow-in-call-to-crc32_le.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Torsten Hilbrich <[email protected]>
Date: Fri, 24 Jun 2016 14:50:18 -0700
Subject: fs/nilfs2: fix potential underflow in call to crc32_le

From: Torsten Hilbrich <[email protected]>

commit 63d2f95d63396059200c391ca87161897b99e74a upstream.

The value `bytes' comes from the filesystem which is about to be mounted. We cannot trust that the value is always in the range we expect it to be.

Check its value before using it to calculate the length for the crc32_le call. It value must be larger (or equal) sumoff + 4.

This fixes a kernel bug when accidentially mounting an image file which had the nilfs2 magic value 0x3434 at the right offset 0x406 by chance. The bytes 0x01 0x00 were stored at 0x408 and were interpreted as a s_bytes value of 1. This caused an underflow when substracting sumoff + 4 (20) in the call to crc32_le.

  BUG: unable to handle kernel paging request at ffff88021e600000
  IP:  crc32_le+0x36/0x100
  ...
  Call Trace:
    nilfs_valid_sb.part.5+0x52/0x60 [nilfs2]
    nilfs_load_super_block+0x142/0x300 [nilfs2]
    init_nilfs+0x60/0x390 [nilfs2]
    nilfs_mount+0x302/0x520 [nilfs2]
    mount_fs+0x38/0x160
    vfs_kern_mount+0x67/0x110
    do_mount+0x269/0xe00
    SyS_mount+0x9f/0x100
    entry_SYSCALL_64_fastpath+0x16/0x71

---
 fs/nilfs2/the_nilfs.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -443,7 +443,7 @@ static int nilfs_valid_sb(struct nilfs_s
 	if (!sbp || le16_to_cpu(sbp->s_magic) != NILFS_SUPER_MAGIC)
 		return 0;
 	bytes = le16_to_cpu(sbp->s_bytes);
-	if (bytes > BLOCK_SIZE)
+	if (bytes < sumoff + 4 || bytes > BLOCK_SIZE)
 		return 0;
 	crc = crc32_le(le32_to_cpu(sbp->s_crc_seed), (unsigned char *)sbp,
 		       sumoff);

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/fs-nilfs2-fix-potential-underflow-in-call-to-crc32_le.patch