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[2003:d8:2f2a:e200:f98f:8d71:83f:f88]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee0fbc7107sm19834232f8f.30.2025.09.22.01.44.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Sep 2025 01:44:01 -0700 (PDT) Message-ID: <715052fa-2459-4785-87fa-04c8cf30debb@redhat.com> Date: Mon, 22 Sep 2025 10:43:59 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] fs/proc/task_mmu: check p->vec_buf for NULL To: Jakub Acs , linux-fsdevel@vger.kernel.org Cc: Andrew Morton , Vlastimil Babka , Lorenzo Stoakes , Jinjiang Tu , Suren Baghdasaryan , Penglei Jiang , Mark Brown , Baolin Wang , Ryan Roberts , Andrei Vagin , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Stephen Rothwell , Muhammad Usama Anjum , linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20250922082206.6889-1-acsjakub@amazon.de> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 22.09.25 10:22, 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 > > > > [ 44.946828] Call Trace: > [ 44.947030] > [ 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 Acked-by: David Hildenbrand -- Cheers David / dhildenb