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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-12-23 at 02:55 -0800, Breno Leitao wrote: > Add a WARN_ON_ONCE() check to detect mm_struct instances that are > missing user_ns initialization when passed to kthread_use_mm(). >=20 > 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. >=20 > 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. >=20 > Adding this warning helps catch similar bugs early during development > rather than waiting for hard-to-debug NULL pointer crashes in > production. >=20 > Signed-off-by: Breno Leitao Acked-by: Rik van Riel --=20 All Rights Reversed.