CVE-2026-98787: bpf: Fix missing migration protection in __rhtab_map_lookup_and_delete_batch()

CVE-2026-98787: bpf: Fix missing migration protection in __rhtab_map_lookup_and_delete_batch()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

bpf: Fix missing migration protection in __rhtab_map_lookup_and_delete_batch()

bpf_mem_cache_free_rcu() uses this_cpu_ptr() which requires migration
to be disabled. All callers of rhtab_delete_elem() disable migration
except __rhtab_map_lookup_and_delete_batch(), which calls it under
rcu_read_lock() only.

On CONFIG_PREEMPT_RCU, rcu_read_lock() does not disable preemption or
migration, so the task can migrate between CPUs during the delete loop,
causing this_cpu_ptr() to trigger:

  BUG: using smp_processor_id() in preemptible [00000000] code

Fix by wrapping the delete loop in migrate_disable()/migrate_enable()
in __rhtab_map_lookup_and_delete_batch(), matching the migration
protection that the other callers already provide.

The Linux kernel CVE team has assigned CVE-2026-98787 to this issue.


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

	Issue introduced in 7.2 with commit 818e0084822742fc00eacbf5df3476a5e72c7d0e and fixed in 7.2.10 with commit 94f41ec5fa578765b74ad5736c2f029e7aabc46d
	Issue introduced in 7.2 with commit 818e0084822742fc00eacbf5df3476a5e72c7d0e and fixed in 7.3-rc6 with commit de020dc8049bfb2b22e3b6d99c031feb2e22d112

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-2026-98787
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:
	kernel/bpf/hashtab.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/94f41ec5fa578765b74ad5736c2f029e7aabc46d
	https://git.kernel.org/stable/c/de020dc8049bfb2b22e3b6d99c031feb2e22d112