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Mon, 22 Sep 2025 10:41:17 +0200 (CEST) Message-ID: Date: Mon, 22 Sep 2025 13:39:02 +0500 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: usama.anjum@collabora.com, Andrew Morton , David Hildenbrand , Vlastimil Babka , Lorenzo Stoakes , Jinjiang Tu , Suren Baghdasaryan , Penglei Jiang , Mark Brown , Baolin Wang , Ryan Roberts , Andrei Vagin , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Stephen Rothwell , linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v3] fs/proc/task_mmu: check p->vec_buf for NULL To: Jakub Acs References: <20250922082206.6889-1-acsjakub@amazon.de> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: <20250922082206.6889-1-acsjakub@amazon.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 > > > > [ 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 > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Vlastimil Babka > Cc: Lorenzo Stoakes > Cc: Jinjiang Tu > Cc: Suren Baghdasaryan > Cc: Penglei Jiang > Cc: Mark Brown > Cc: Baolin Wang > Cc: Ryan Roberts > Cc: Andrei Vagin > Cc: "Michał Mirosław" > Cc: Stephen Rothwell > Cc: Muhammad Usama Anjum > Cc: linux-kernel@vger.kernel.org > Cc: linux-fsdevel@vger.kernel.org > Cc: stable@vger.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 --- Thanks, Usama