CVE-2026-74728: xfs: handle NULL b_addr in xfs_buf_free

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

xfs: handle NULL b_addr in xfs_buf_free

When xfs_buf_alloc_backing_mem() fails, xfs_buf_free() is called with
bp->b_addr still NULL.  The code falls through to the folio_put path
which calls virt_to_folio(NULL), dereferencing an invalid address and
causing a kernel crash.

 Call Trace:
  xfs_buf_free+0x25f/0x510
  xfs_buf_alloc+0xc98/0x19b0
  xfs_buf_find_insert+0x55/0x14d0
  xfs_buf_get_map+0x122b/0x17c0
  xfbtree_init_leaf_block+0x11c/0x4a0
  xfbtree_init+0x1bb/0x460
  xrep_rmap_setup_scan+0x100/0x1f0
  xrep_rmapbt+0x41/0xc0

Fix this by skipping folio_put() when bp->b_addr is NULL.

The Linux kernel CVE team has assigned CVE-2026-74728 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.9 with commit 5076a6040ca1613e616d84aecfaac5f932db84e0 and fixed in 6.18.45 with commit ccf6738adcafa5ddbddc4e71b45d8a51b86643c7
	Issue introduced in 6.9 with commit 5076a6040ca1613e616d84aecfaac5f932db84e0 and fixed in 7.1.9 with commit 3aa0c1d23ee1b9d9b340fb2f4736536e1408d706
	Issue introduced in 6.9 with commit 5076a6040ca1613e616d84aecfaac5f932db84e0 and fixed in 7.2 with commit d852729c5f4f830fbe7413df032e29459b3daf83

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74728
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/xfs/xfs_buf.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ccf6738adcafa5ddbddc4e71b45d8a51b86643c7
	https://git.kernel.org/stable/c/3aa0c1d23ee1b9d9b340fb2f4736536e1408d706
	https://git.kernel.org/stable/c/d852729c5f4f830fbe7413df032e29459b3daf83