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Tue, 23 Dec 2025 02:56:08 -0800 (PST) Received: from localhost ([2a03:2880:10ff:4c::]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-65d0f723ab6sm8713620eaf.17.2025.12.23.02.56.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Dec 2025 02:56:07 -0800 (PST) From: Breno Leitao Date: Tue, 23 Dec 2025 02:55:44 -0800 Subject: [PATCH 2/2] kthread: Warn if mm_struct lacks user_ns in kthread_use_mm() 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-v1-2-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 Add a WARN_ON_ONCE() check to detect mm_struct instances that are missing user_ns initialization when passed to kthread_use_mm(). When a kthread adopts an mm via kthread_use_mm(), LSM hooks and capability checks may access current->mm->user_ns for credential validation. If user_ns is NULL, this leads to a NULL pointer dereference crash. This was observed with efi_mm on arm64, where commit a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption") introduced kthread_use_mm(&efi_mm), but efi_mm lacked user_ns initialization, causing crashes during /proc access. Adding this warning helps catch similar bugs early during development rather than waiting for hard-to-debug NULL pointer crashes in production. Signed-off-by: Breno Leitao --- kernel/kthread.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/kthread.c b/kernel/kthread.c index 99a3808d086f..39511dd2abc9 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1599,6 +1599,7 @@ void kthread_use_mm(struct mm_struct *mm) WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD)); WARN_ON_ONCE(tsk->mm); + WARN_ON_ONCE(!mm->user_ns); /* * It is possible for mm to be the same as tsk->active_mm, but -- 2.47.3