In the Linux kernel, the following vulnerability has been resolved: xfs: bounds-check buffer log item's dirty bitmap xlog_recover_do_reg_b

In the Linux kernel, the following vulnerability has been resolved:

xfs: bounds-check buffer log item's dirty bitmap

xlog_recover_do_reg_buffer() replays each dirty region described by a
buffer log item's bitmap into the buffer read for that item:

 1memcpy(xfs_buf_offset(bp, (uint)bit << XFS_BLF_SHIFT),
 2	item->ri_buf[i].iov_base,
 3	nbits << XFS_BLF_SHIFT);

The destination offset (bit/nbits, from the logged dirty bitmap) and the
buffer size (from the logged blf_len) are both attacker-controlled and
otherwise unrelated, yet the only thing bounding the copy is an ASSERT(),
which compiles away on production kernels. A crafted image logging a
small blf_len together with a bitmap bit past the end of that buffer
drives the memcpy() past the buffer's allocation, corrupting adjacent
kernel heap during mount-time log recovery. This is reachable by anyone
who can get a crafted image mounted -- the malicious-filesystem threat
model XFS already guards against elsewhere.

Turn the ASSERT() into a real XFS_IS_CORRUPT() check that aborts recovery
of the buffer with -EFSCORRUPTED, consistent with the validate-and-fail
idiom already used in xlog_recover_do_inode_buffer() and
xfs_dquot_item_recover.c. xlog_recover_do_reg_buffer() therefore becomes
STATIC int and its three callers propagate the error.

Found and confirmed with KASAN on a CONFIG_XFS_DEBUG=n build: the crafted
image trips a slab-out-of-bounds write before this change and fails
recovery cleanly with -EFSCORRUPTED after it.