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From: Muchun Song In-Reply-To: <20260809043250.2917406-1-souravpanda@google.com> Date: Sun, 9 Aug 2026 14:58:12 +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: quoted-printable Message-Id: References: <20260809043250.2917406-1-souravpanda@google.com> To: Sourav Panda X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 267EEC0007 X-Rspam-User: X-Stat-Signature: o3ie7md6htagteuz41wpguqexx4ytdns X-HE-Tag: 1786258713-486449 X-HE-Meta: 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 TlfeJ5MH /Prgc5exemV9OOder4QTNrwdosbqPV8Imikhz34zBMUK9OlVCIx9hmF2cU85B3MiVbn646QMmZbFGKbJX2fFMVzfv/lsLFTTo9AhO8cL1/I7+YNY8T1Xm0XsokdZnvrWrEsmtpm52soRi3gA0OZ4v3vm3BWKbDwSX+dA33HhNRJhIFLkCRKHNYLfWw98JNLBdy6C+gUB5FPQJAOOBR4mDTOkG3VBlvNla9EWVUolrrd1QhceWtZMcBqKPEONXOmKveWTGwgaMWVaEM5CoQvd3f5JIkXGyNLsebaby2BYf2uXJ/tLM8rxJ/vXlh8H1sv94URBNzGdVkSH8y3Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Aug 9, 2026, at 12:32, Sourav Panda wrote: >=20 > 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(). >=20 > 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. >=20 > 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. >=20 > Fix this by checking if nodemask is NULL in > hugetlb_cma_alloc_frozen_folio() and defaulting it to > cpuset_current_mems_allowed (safely read using a seqcount retry loop). > 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. >=20 > =46rom 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. >=20 > This can be reproduced by booting a VM with two NUMA nodes, = restricting > CMA to Node 1 (e.g., hugetlb_cma=3D1:1G default_hugepagesz=3D1G > hugepagesz=3D1G hugepages=3D0), 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: >=20 > void *ptr =3D mmap(NULL, 1UL << 30, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | > MAP_HUGE_1GB | MAP_NORESERVE, -1, 0); > unsigned long nodemask =3D 1; /* Node 0 */ > mbind(ptr, 1UL << 30, MPOL_PREFERRED_MANY, &nodemask, > sizeof(nodemask) * 8, 0); > memset(ptr, 0, 1UL << 30); /* Trigger fault */ >=20 > This results in a NULL pointer dereference: >=20 > 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 >=20 > Fixes: eb02f14c4a2b ("mm/hugetlb: allow overcommitting gigantic = hugepages") > Cc: stable@vger.kernel.org > Signed-off-by: Sourav Panda > --- > Changes in v5: > - Replaced defaulting nodemask to &node_states[N_MEMORY] with safely = reading > cpuset_current_mems_allowed using a seqcount retry loop, ensuring = fallback > allocations comply with task hardwall cpusets as suggested by Usama = Arif. > - v4: = https://lore.kernel.org/linux-mm/20260726072935.3513996-1-souravpanda@goog= le.com/ > - v3: = https://lore.kernel.org/linux-mm/20260705175119.440599-1-souravpanda@googl= e.com/ > - v2: = https://lore.kernel.org/linux-mm/20260704174930.2885785-1-souravpanda@goog= le.com/ > - v1: = https://lore.kernel.org/linux-mm/20260702215713.627941-1-souravpanda@googl= e.com/ >=20 > mm/hugetlb_cma.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) >=20 > diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c > index 39344d6c78d8..3ae9347078e9 100644 > --- a/mm/hugetlb_cma.c > +++ b/mm/hugetlb_cma.c > @@ -3,6 +3,7 @@ > #include > #include > #include > +#include > #include >=20 > #include > @@ -30,11 +31,23 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int = order, gfp_t gfp_mask, > int node; > struct folio *folio; > struct page *page =3D NULL; > + nodemask_t local_node_mask; >=20 > if (!hugetlb_cma_size) > return NULL; >=20 > - if (hugetlb_cma[nid]) > + if (!nodemask) { > + unsigned int cpuset_mems_cookie; > + > + do { > + cpuset_mems_cookie =3D = read_mems_allowed_begin(); > + local_node_mask =3D cpuset_current_mems_allowed; I think it only makes sense to move cma_alloc_frozen_compound() inside = the loop. Otherwise, during subsequent memory allocations, we could still = face unexpected allocation failures. Muchun, Thanks. > + } while (read_mems_allowed_retry(cpuset_mems_cookie)); > + > + nodemask =3D &local_node_mask; > + } > + > + if (hugetlb_cma[nid] && node_isset(nid, *nodemask)) > page =3D cma_alloc_frozen_compound(hugetlb_cma[nid], = order); >=20 > if (!page && !(gfp_mask & __GFP_THISNODE)) { > --=20 > 2.55.0