linux-cve-announce - CVE-2024-56612: mm/gup: handle NULL pages in unpin_user

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Message-ID: <2024122707-CVE-2024-56612-a24e@gregkh>
Date: Fri, 27 Dec 2024 15:51:19 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56612: mm/gup: handle NULL pages in unpin_user_pages()

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

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

mm/gup: handle NULL pages in unpin_user_pages()

The recent addition of "pofs" (pages or folios) handling to gup has a
flaw: it assumes that unpin_user_pages() handles NULL pages in the pages**
array.  That's not the case, as I discovered when I ran on a new
configuration on my test machine.

Fix this by skipping NULL pages in unpin_user_pages(), just like
unpin_folios() already does.

Details: when booting on x86 with "numa=fake=2 movablecore=4G" on Linux
6.12, and running this:

    tools/testing/selftests/mm/gup_longterm

...I get the following crash:

BUG: kernel NULL pointer dereference, address: 0000000000000008
RIP: 0010:sanity_check_pinned_pages+0x3a/0x2d0
...
Call Trace:
 <TASK>
 ? __die_body+0x66/0xb0
 ? page_fault_oops+0x30c/0x3b0
 ? do_user_addr_fault+0x6c3/0x720
 ? irqentry_enter+0x34/0x60
 ? exc_page_fault+0x68/0x100
 ? asm_exc_page_fault+0x22/0x30
 ? sanity_check_pinned_pages+0x3a/0x2d0
 unpin_user_pages+0x24/0xe0
 check_and_migrate_movable_pages_or_folios+0x455/0x4b0
 __gup_longterm_locked+0x3bf/0x820
 ? mmap_read_lock_killable+0x12/0x50
 ? __pfx_mmap_read_lock_killable+0x10/0x10
 pin_user_pages+0x66/0xa0
 gup_test_ioctl+0x358/0xb20
 __se_sys_ioctl+0x6b/0xc0
 do_syscall_64+0x7b/0x150
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

The Linux kernel CVE team has assigned CVE-2024-56612 to this issue.


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

	Issue introduced in 6.12 with commit 94efde1d15399f5c88e576923db9bcd422d217f2 and fixed in 6.12.5 with commit 69d319450d1c651f3b05cd820ff285fdd810c032
	Issue introduced in 6.12 with commit 94efde1d15399f5c88e576923db9bcd422d217f2 and fixed in 6.13-rc2 with commit a1268be280d8e484ab3606d7476edd0f14bb9961

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-2024-56612
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:
	mm/gup.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/69d319450d1c651f3b05cd820ff285fdd810c032
	https://git.kernel.org/stable/c/a1268be280d8e484ab3606d7476edd0f14bb9961