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b=V++APQdav59a96D19Bw6Q+BKElEnxWZXtnDS0ZWNXgt2ft1PMcLZYLfkE85fSRbpk +tHp+5bqUDzoTZ4QBZY3lUItBQnMcwHEcu2Ii5rwe7rHBs8qZMJcu8XAjLz436egUb Qg0UbksZCPLgM8IcUqWepEXgStmbMeeh/sj5ayqY= Date: Mon, 27 Jul 2026 17:57:04 -0700 From: Andrew Morton To: Sourav Panda Cc: muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, surenb@google.com, fvdl@google.com, gthelen@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Usama Arif , Shakeel Butt , Kefeng Wang Subject: Re: [PATCH v4] mm/hugetlb_cma: Fix null nodemask dereference in hugetlb_cma_alloc_frozen_folio Message-Id: <20260727175704.0e4ccd4a6201435a6284d260@linux-foundation.org> In-Reply-To: <20260726072935.3513996-1-souravpanda@google.com> References: <20260726072935.3513996-1-souravpanda@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: ekt5fhkposeax6sbaihycx5r74giijxx X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C6D29C0004 X-HE-Tag: 1785200226-10116 X-HE-Meta: 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 78TLJTwW tKz3wxpc8PXx5t2SO0qBkowQe7ZbjcortHYumtl9ZPGJVG8BYY+HDVfIlxsENzHmUQCfVlCsFFEANJZ/u14saxeyAx6B4MrYo1vYJu5iZ6DwUhXHNo+LSShMfbNf4w1syK5eORpyHSXSjbYH/2KdsTiUt5V6jVeyZ4vYp6gg+i7iAOD5ltVvOPs3NTyJSuRRXE9lY858QxlvA/bdnvyPdIpnQdOylep8mLoeZII07Yu7is46QyImqGt3CephHPozsT5jfzQ13Vsh16+rPsZuE0pBwtH+xL20Ivhny8O9AWx3XW6x2w8KBMesTyYuCq89u4Ydc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 26 Jul 2026 07:29:34 +0000 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(). > > hugetlb_cma_alloc_frozen_folio() blindly dereferences the nodemask in > node_isset(nid, *nodemask) and for_each_node_mask(node, *nodemask), > leading to a null pointer dereference kernel panic. > > Fix this by checking if nodemask is NULL in > hugetlb_cma_alloc_frozen_folio() and defaulting it to > node_states[N_MEMORY]. This allows hugetlb_cma allocations to fall > back to any node with memory, keeping behavior consistent with > alloc_contig_frozen_pages() and alloc_buddy_frozen_folio(). > > >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 Thanks. I'll queue this as a hotfix while we await review. > Fixes: eb02f14c4a2b ("mm/hugetlb: allow overcommitting gigantic hugepages") It's a good idea to cc the people who were involved in the to-be-fixed patch - Author and Reviewers. > > ... > > --- a/mm/hugetlb_cma.c > +++ b/mm/hugetlb_cma.c > @@ -34,7 +34,10 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask, > if (!hugetlb_cma_size) > return NULL; > > - if (hugetlb_cma[nid]) > + if (!nodemask) > + nodemask = &node_states[N_MEMORY]; > + > + if (hugetlb_cma[nid] && node_isset(nid, *nodemask)) > page = cma_alloc_frozen_compound(hugetlb_cma[nid], order); > > if (!page && !(gfp_mask & __GFP_THISNODE)) { > -- > 2.55.0