linux-kernel - Re: [PATCH v3] fs/proc/task_mmu: check p->vec

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <a5400d9f-fb72-41ca-bedc-aa1c880a2234@collabora.com>
Date: Mon, 22 Sep 2025 13:39:02 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Jakub Acs <acsjakub@...zon.de>
Cc: usama.anjum@...labora.com, Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Jinjiang Tu <tujinjiang@...wei.com>, Suren Baghdasaryan <surenb@...gle.com>,
 Penglei Jiang <superman.xpt@...il.com>, Mark Brown <broonie@...nel.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ryan Roberts <ryan.roberts@....com>, Andrei Vagin <avagin@...il.com>,
 Michał Mirosław <mirq-linux@...e.qmqm.pl>,
 Stephen Rothwell <sfr@...b.auug.org.au>, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3] fs/proc/task_mmu: check p->vec_buf for NULL

Added mm list to cc as well

On 9/22/25 1:22 PM, Jakub Acs wrote:
> When PAGEMAP_SCAN ioctl invoked with vec_len = 0 reaches
> pagemap_scan_backout_range(), kernel panics with null-ptr-deref:
> 
> [   44.936808] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
> [   44.937797] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> [   44.938391] CPU: 1 UID: 0 PID: 2480 Comm: reproducer Not tainted 6.17.0-rc6 #22 PREEMPT(none)
> [   44.939062] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> [   44.939935] RIP: 0010:pagemap_scan_thp_entry.isra.0+0x741/0xa80
> 
> <snip registers, unreliable trace>
> 
> [   44.946828] Call Trace:
> [   44.947030]  <TASK>
> [   44.949219]  pagemap_scan_pmd_entry+0xec/0xfa0
> [   44.952593]  walk_pmd_range.isra.0+0x302/0x910
> [   44.954069]  walk_pud_range.isra.0+0x419/0x790
> [   44.954427]  walk_p4d_range+0x41e/0x620
> [   44.954743]  walk_pgd_range+0x31e/0x630
> [   44.955057]  __walk_page_range+0x160/0x670
> [   44.956883]  walk_page_range_mm+0x408/0x980
> [   44.958677]  walk_page_range+0x66/0x90
> [   44.958984]  do_pagemap_scan+0x28d/0x9c0
> [   44.961833]  do_pagemap_cmd+0x59/0x80
> [   44.962484]  __x64_sys_ioctl+0x18d/0x210
> [   44.962804]  do_syscall_64+0x5b/0x290
> [   44.963111]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
> vec_len = 0 in pagemap_scan_init_bounce_buffer() means no buffers are
> allocated and p->vec_buf remains set to NULL.
> 
> This breaks an assumption made later in pagemap_scan_backout_range(),
> that page_region is always allocated for p->vec_buf_index.
> 
> Fix it by explicitly checking p->vec_buf for NULL before dereferencing.
> 
> Other sites that might run into same deref-issue are already (directly
> or transitively) protected by checking p->vec_buf.
> 
> Note:
> From PAGEMAP_SCAN man page, it seems vec_len = 0 is valid when no output
> is requested and it's only the side effects caller is interested in,
> hence it passes check in pagemap_scan_get_args().
> 
> This issue was found by syzkaller.
> 
> Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs")
> Signed-off-by: Jakub Acs <acsjakub@...zon.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Cc: Jinjiang Tu <tujinjiang@...wei.com>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Penglei Jiang <superman.xpt@...il.com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Andrei Vagin <avagin@...il.com>
> Cc: "Michał Mirosław" <mirq-linux@...e.qmqm.pl>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-fsdevel@...r.kernel.org
> Cc: stable@...r.kernel.org
> ---
> v1 -> v2: check p->vec_buf instead of cur_buf
> v2 -> v3: fix commit title
> 
> v1: https://lore.kernel.org/all/20250919142106.43527-1-acsjakub@amazon.de/ 
> v2: https://lore.kernel.org/all/20250922081713.77303-1-acsjakub@amazon.de/
> 
>  fs/proc/task_mmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 29cca0e6d0ff..b26ae556b446 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -2417,6 +2417,9 @@ static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
>  {
>  	struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
>  
> +	if (!p->vec_buf)
> +		return;
> +
Reviewed-by: Muhammad Usama Anjum <usama.anjum@...labora.com>


---
Thanks,
Usama