From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta0.migadu.com (out-182.mta0.migadu.com [91.218.175.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 642E434040A for ; Tue, 11 Aug 2026 07:08:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786432104; cv=none; b=fth4JZJy/ooe/5b+JrcWe/rWWDBzCEGF8zCzd9c+lvr9Mnu3KC385Vj0FEKmQ0pCYm5ZjrrkO5rh7DHn+qPGWU65PDhhwEHYNR6e3wguFym9ILknT9xt9wuUQJ1lDv6eAjxlnqY9UO37iJZF1LElN/hFvZMyulIXjc78dDefigY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786432104; c=relaxed/simple; bh=NB+cCLRp0sbKyPnuSh6khlZte4YAh7IztVbvEVlyjqo=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=dD9b3EqTHm0xlSN5G4oAiQVemyvnMjIhS8VZRXL6AYYX2A5QJUGYlGQXqYJB4YxVZIn8y1xisX5C03HqSlMKfE0zmYT+INHTHfrxOKNpzrE5nzIliI7+tFPfgLhryPJzilTkmFMDdiOIFFKgZJhrK0FOo8hkaTQs4/VZqZTQEhc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=gGwyF+7g; arc=none smtp.client-ip=91.218.175.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="gGwyF+7g" Content-Type: text/plain; charset=us-ascii DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1786432097; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=H4jTbw0Wv+xPvXVSegCeaGGpLthSdk7LTeihL94Ey1U=; b=gGwyF+7gspN8TLlI7dUBS3GUsQYtjH0gz1vLncu6CTXLZFQi2QtIZTb1yr0d5jYuebYTZu CBroq19U1h12HEWxIXiIG57UUX2wCWEvTcPJJnTJEHYdQ80W/VHigwQcqVIQTdqVtz5Eh6 VVtNMayzoaIuHHfpS7IZUTotbKZ9ABs= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.600.51.1.1\)) Subject: Re: [PATCH v7] mm/hugetlb_cma: Fix null nodemask dereference in hugetlb_cma_alloc_frozen_folio X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20260811052909.475635-1-souravpanda@google.com> Date: Tue, 11 Aug 2026 15:07:56 +0800 Cc: osalvador@suse.de, akpm@linux-foundation.org, usama.arif@linux.dev, shakeel.butt@linux.dev, wangkefeng.wang@huawei.com, anshuman.khandual@arm.com, david@kernel.org, surenb@google.com, fvdl@google.com, gthelen@google.com, hannes@cmpxchg.org, riel@surriel.com, sj@kernel.org, vbabka@suse.cz, mhocko@suse.com, bjackman@google.com, zi.yan@sent.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: 7bit Message-Id: References: <20260811052909.475635-1-souravpanda@google.com> To: Sourav Panda X-Migadu-Flow: FLOW_OUT > On Aug 11, 2026, at 13:29, Sourav Panda wrote: > > alloc_buddy_hugetlb_folio_with_mpol() can pass a NULL nodemask to > alloc_fresh_hugetlb_folio() as a fallback to allocate from all > nodes. If order is gigantic, alloc_fresh_hugetlb_folio() propagates > the NULL nodemask down to hugetlb_cma_alloc_frozen_folio() via > alloc_gigantic_frozen_folio(). > > Additionally, hugetlb_cma_alloc_frozen_folio() previously attempted > allocation on hugetlb_cma[nid] without verifying if nid is included in > the caller's nodemask. Adding a node_isset(nid, *nodemask) check ensures > the initial preferred node allocation honors the memory policy / nodemask. > > However, hugetlb_cma_alloc_frozen_folio() dereferences the nodemask in > node_isset(nid, *nodemask) and for_each_node_mask(node, *nodemask), > leading to a null pointer dereference kernel panic when nodemask is NULL. > > Fix this by checking if nodemask is NULL in > hugetlb_cma_alloc_frozen_folio() and defaulting it to > cpuset_current_mems_allowed. Enclose the allocation attempts within > the cpuset seqcount retry loop so that if the cpuset changes concurrently > during allocation, the attempts are retried using the updated nodemask. > This ensures that the initial node check and fallback loop safely honor > the task's cpuset without violating cpuset constraints or causing NULL > pointer dereferences or unexpected allocation failures. > > From a userspace perspective, this bug allows an unprivileged user to > crash the kernel (trigger a panic) by requesting a gigantic hugepage > allocation with MPOL_PREFERRED_MANY on a system where CMA is only > configured on a subset of NUMA nodes. > > This can be reproduced by booting a VM with two NUMA nodes, restricting > CMA to Node 1 (e.g., hugetlb_cma=1:1G default_hugepagesz=1G > hugepagesz=1G hugepages=0), and running a program that allocates a > 1GB hugepage area without reserving, restricts allocation to Node 0 > using mbind() with MPOL_PREFERRED_MANY, and triggers a page fault: > > void *ptr = mmap(NULL, 1UL << 30, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | > MAP_HUGE_1GB | MAP_NORESERVE, -1, 0); > unsigned long nodemask = 1; /* Node 0 */ > mbind(ptr, 1UL << 30, MPOL_PREFERRED_MANY, &nodemask, > sizeof(nodemask) * 8, 0); > memset(ptr, 0, 1UL << 30); /* Trigger fault */ > > This results in a NULL pointer dereference: > > BUG: kernel NULL pointer dereference, address: 0000000000000000 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > Oops: Oops: 0000 [#1] SMP NOPTI > RIP: 0010:hugetlb_cma_alloc_frozen_folio+0x75/0x120 > Call Trace: > > only_alloc_fresh_hugetlb_folio.isra.0+0x2c/0x160 > alloc_surplus_hugetlb_folio+0x6d/0x100 > alloc_hugetlb_folio+0x3c5/0x660 > hugetlb_no_page+0x3d9/0x650 > > Fixes: eb02f14c4a2b ("mm/hugetlb: allow overcommitting gigantic hugepages") > Cc: stable@vger.kernel.org > Signed-off-by: Sourav Panda Reviewed-by: Muchun Song Thanks.