From: Rik van Riel <riel@surriel.com>
To: Breno Leitao <leitao@debian.org>,
Ard Biesheuvel <ardb@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, puranjay@kernel.org,
usamaarif642@gmail.com, kernel-team@meta.com
Subject: Re: [PATCH 2/2] kthread: Warn if mm_struct lacks user_ns in kthread_use_mm()
Date: Tue, 23 Dec 2025 14:31:32 -0500 [thread overview]
Message-ID: <4d867df02dcc3cc8f519903282f6e63b2974a461.camel@surriel.com> (raw)
In-Reply-To: <20251223-efi_fix_619-v1-2-e0146b8b9d73@debian.org>
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().
>
> 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 <leitao@debian.org>
Acked-by: Rik van Riel <riel@surriel.com>
--
All Rights Reversed.
next prev parent reply other threads:[~2025-12-23 19:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-23 10:55 [PATCH 0/2] arm64: efi: Fix NULL pointer crash in 6.19-rc2 Breno Leitao
2025-12-23 10:55 ` [PATCH 1/2] arm64: efi: Fix NULL pointer dereference by initializing user_ns Breno Leitao
2025-12-23 19:24 ` Rik van Riel
2025-12-23 10:55 ` [PATCH 2/2] kthread: Warn if mm_struct lacks user_ns in kthread_use_mm() Breno Leitao
2025-12-23 19:31 ` Rik van Riel [this message]
2025-12-26 10:10 ` [PATCH 0/2] arm64: efi: Fix NULL pointer crash in 6.19-rc2 Ard Biesheuvel
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