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

Overview

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:

memcpy(xfs_buf_offset(bp, (uint)bit << XFS_BLF_SHIFT),
	item->ri_buf[i].iov_base,
	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.

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < acb4e26295e7f0e685815a3fd3d70bd8329cefa1
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f3859c35a4fbc1c1c58431f684f808e43696891d
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f7b5fa83e2c192be922121b764415fa8c7549ea1
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b7528b42813f02724a78fce1da24d69d1bfc4d38
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 7e32d4eebae6ca24f8a673c107fd7eca1f47afc2
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f8288214459ead7e87d26e5822f62c14a4f2ed6b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < edaf5b6bd625356893da20d69a259b34a9de2694
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 813f8136a2ce1fee266d02a7df73db6e8a541604
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.