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Tue, 23 Dec 2025 02:56:07 -0800 (PST) Received: from localhost ([2a03:2880:10ff:49::]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7cc6673bdabsm9065064a34.10.2025.12.23.02.56.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Dec 2025 02:56:06 -0800 (PST) From: Breno Leitao Date: Tue, 23 Dec 2025 02:55:43 -0800 Subject: [PATCH 1/2] arm64: efi: Fix NULL pointer dereference by initializing user_ns Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251223-efi_fix_619-v1-1-e0146b8b9d73@debian.org> References: <20251223-efi_fix_619-v1-0-e0146b8b9d73@debian.org> In-Reply-To: <20251223-efi_fix_619-v1-0-e0146b8b9d73@debian.org> To: Ard Biesheuvel , Catalin Marinas , Will Deacon Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, riel@surriel.com, puranjay@kernel.org, usamaarif642@gmail.com, Breno Leitao , kernel-team@meta.com X-Mailer: b4 0.15-dev-47773 X-Developer-Signature: v=1; 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a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D Linux 6.19-rc2 (9448598b22c5 ("Linux 6.19-rc2")) is crashing with a NULL pointer dereference on arm64 hosts: Unable to handle kernel NULL pointer dereference at virtual address 00000000000000c8 pc : cap_capable (security/commoncap.c:82 security/commoncap.c:128) Call trace: cap_capable (security/commoncap.c:82 security/commoncap.c:128) (P) security_capable (security/security.c:?) ns_capable_noaudit (kernel/capability.c:342 kernel/capability.c:381) __ptrace_may_access (./include/linux/rcupdate.h:895 kernel/ptrace.c:326) ptrace_may_access (kernel/ptrace.c:353) do_task_stat (fs/proc/array.c:467) proc_tgid_stat (fs/proc/array.c:673) proc_single_show (fs/proc/base.c:803) I've bissected the problem to commit a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption"). >From my analyzes, the crash occurs because efi_mm lacks a user_ns field initialization. This was previously harmless, but commit a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption") changed the EFI runtime call path to use kthread_use_mm(&efi_mm), which temporarily adopts efi_mm as the current mm for the calling kthread. When a thread has an active mm, LSM hooks like cap_capable() expect mm->user_ns to be valid for credential checks. With efi_mm.user_ns being NULL, capability checks during possible /proc access dereference the NULL pointer and crash. Fix by initializing efi_mm.user_ns to &init_user_ns. Fixes: a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption") Signed-off-by: Breno Leitao --- drivers/firmware/efi/efi.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index a9070d00b833..55452e61af31 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -73,6 +73,7 @@ struct mm_struct efi_mm = { MMAP_LOCK_INITIALIZER(efi_mm) .page_table_lock = __SPIN_LOCK_UNLOCKED(efi_mm.page_table_lock), .mmlist = LIST_HEAD_INIT(efi_mm.mmlist), + .user_ns = &init_user_ns, .cpu_bitmap = { [BITS_TO_LONGS(NR_CPUS)] = 0}, #ifdef CONFIG_SCHED_MM_CID .mm_cid.lock = __RAW_SPIN_LOCK_UNLOCKED(efi_mm.mm_cid.lock), -- 2.47.3