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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 X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 9427F40003 X-Stat-Signature: hsi43hfbay86cy39tznbbtkfhqjujkuf X-HE-Tag: 1786432099-378782 X-HE-Meta: U2FsdGVkX1/u8sYkhjXlJsXgm2AppCfB4mqyllVcajgI1MaZd4cpQ6CJqmdhUWimkJj+S8rcYB/Brm4EVyGDtqxcnBzTKKDXWQ+di8V3cyRAmV/asTR2/K2VKwk6IQMMe2yg9TFvdOHP/KDwg9ypwtNZzm5QHhuWVolY+vNClJCmd7UX+rI+1IKBgnvB0JXls2996nA5XG2+caibwBDf6Kg6djaZNCAN7721aiNDsbBf07GHiHa+LWK+D9Rl42wpDDuUqMwJBC3RvkF+OX0+PnitzW9nyzNmaHaNsqXSJqunlLHwCZTuI300WNJC1KlV5RBhdnq6TCtNsmGoo1VmWpdZtTODmsAKXLTgR2P248zOqCcCvpGe+xyhtcK/7VcjbYOor0/ACYHEP0FJudpRR/NeWVRVwR5HPWZm1d25YMZT2po3SP9YgR/taD4npLmBPzhh5KucrRBwK/U69zIknrmM/zxrfts1sweprxQJoPTNOKv+sbYi+GpJ0MLBPCxK2CTox2dhKLEmPku0FFExG6+MXZKBKta+j8YhqxiBzKIKLL9X3uyzg6knMrnMcKJIc4id6t1O0HW51pfyOzJzgL4PIl3v/HLrDxPsvYSKizA67MK+dtr/I3rltSpmQXABfsqMMdmdu7CkbJn2+ArhjRVu0YCGXbl1L7v2D10yqJrzniec+H9MbQkgNMpv6l0K/nfW0w9f453ouSsF+e8V36l2SeHaYpcbbLBplWs8rDcWCk1wVD5JrJxarb5b5xcOwejRDfFHi4losP3d4CcLUgIa9JiJ9zIPLTFEUEwEBhFmDO+SGqU6NTMcqochHwK8Fkq+2AVeMUMUK1UBGyD4NDXZZjA7J6ju3psdSSv6pTrd/1BzCsgMtadLHSHa3ueUN0dp4DlsLxB3z5DBqOKJA8sBDUxYQ2EMMeMNpstTNlH5ORznL5f0/1Prl/ILFhhpw6VM/bTh5xU5O4jyFkO 9ZU4aMCQ /qhjQoij8XbC6cMXWiAZlURbejt9MNl5PGCtzC3QtFi32ftKnLXZhJ32XdF4Rc0Dq/8VajTI7FXB7pTfPe5AJPhhq37fjOGpGQvYmc4UPqlLjhg5IWCQTq7EXOICH9DNc6vYRwTpjj8btxa1LfINHdH/99IZRy3WzPUSr+CIlKP+w2J0kS9+WmjLWWUSO1l6Kr6bJ6+0DHurR2fqg4dxcsI3dJTo3EJ/5lgtqvBYB9y5Cv+IOO7oikrcK2WVUiW7furbZ6zrV4BjUG2zTPbxY4eRHhx+vadlF0ddaRHeU7A0bp7e+K3eonpS1GRgrKwKg/Zco9CTSr3j3C1E= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > 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.