From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4D5713AFAFF for ; Mon, 18 May 2026 22:37:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779143876; cv=none; b=F+WFJHbeT7WkbGUWY6wSdhX565kt3d0zU9Q5lZcpMUH5ilIbWvsMfCSvVEKNCQSztmBojMt9TCvrIV5yrDtC8sb+Ku8AW5q8zZuBoM8VUjQY+oZwktf5KTIZqThk++JWvaxbDGgBqYjl5C0q2nsWYWoRHoSWd85gqNbuQ7T/2MA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779143876; c=relaxed/simple; bh=IxSNiaISllfVtHvt5Gju2AVT30PdTibnWQufK4CoGNo=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=Dslg1P8MnQ/JKWiJqglYwY1vSQ8NOxvAshwDNCC7y7rhaQ55Wep/m0uxVuocUZJEeC7ICJI2WwD3x7LhwR+OUQA7SqexGmTmnft+9C7w6DN5WcWQWsNX4TG2m5Bt7Ya4e1g9XYuYHOzsTCUbFZIWLC2y7GIfl+sOkdpfyAMcLn4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=ElMKWvtl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="ElMKWvtl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C557C2BCB7; Mon, 18 May 2026 22:37:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1779143875; bh=IxSNiaISllfVtHvt5Gju2AVT30PdTibnWQufK4CoGNo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ElMKWvtlrYQVJHpqzMtMAQe5BB0aDbgakLhbNKiIyRp+ZoSFA5LC/W42SQzbsdETT OmDX5NorKwzWKT8bVZAiQtWaobbmaFYPkT8wwhHPXcLoip4jmRvhVZc7yJwwDhUgXj Ja7AQEGXYBZ/tFp5h0XvLVPV12vfHioppD/9AuOk= Date: Mon, 18 May 2026 15:37:55 -0700 From: Andrew Morton To: Oleg Nesterov Cc: Tetsuo Handa , Deepanshu Kartikey , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH -mm v2] do_notify_parent: sanitize the valid_signal() checks Message-Id: <20260518153755.f3248bc3725d5b745a6696f9@linux-foundation.org> In-Reply-To: References: <20260316151956.563558-1-kartikey406@gmail.com> <20260317113452.cede9a514dfed36a1cb0e5a9@linux-foundation.org> <5acfea15-f2f7-4498-86e1-a383e17adad0@I-love.SAKURA.ne.jp> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 17 May 2026 09:05:26 +0200 Oleg Nesterov wrote: > On 05/17, Tetsuo Handa wrote: > > > > On 2026/03/18 4:08, Oleg Nesterov wrote: > > > On 03/17, Andrew Morton wrote: > > >> > > >> On Tue, 17 Mar 2026 14:58:18 +0100 Oleg Nesterov wrote: > > >> > > >>> Now that kernel_clone() checks valid_signal(args->exit_signal), the "sig" > > >>> argument of do_notify_parent() must always be valid or we have a bug. > > > > No activity for two months. When is the fix expected to land to upstream? > > This bug allows a local unprivileged user to crash panic_on_warn=1 systems > > by running below program, and therefore should be fixed before Linux 7.1 is > > released. > > This patch depends on > > [PATCH v3] kernel/fork: validate exit_signal in kernel_clone() > https://lore.kernel.org/all/20260316151956.563558-1-kartikey406@gmail.com/ > > but it was merged without the patch above. > > Andrew, that patch is still in mm tree, > > kernel-fork-validate-exit_signal-in-kernel_clone.patch > > could you merge it as well? Thanks, I moved the below out of the 7.2-rc1 queue and into the 7.1-rcX queue. Should this have cc:stable? From: Deepanshu Kartikey Subject: kernel/fork: validate exit_signal in kernel_clone() Date: Mon, 16 Mar 2026 20:49:56 +0530 When a child process exits, it sends exit_signal to its parent via do_notify_parent(). The clone() syscall constructs exit_signal as: (lower_32_bits(clone_flags) & CSIGNAL) CSIGNAL is 0xff, so values in the range 65-255 are possible. However, valid_signal() only accepts signals up to _NSIG (64 on x86_64). A non-zero non-valid exit_signal acts the same as exit_signal == 0: the parent process is not signaled when the child terminates. The syzkaller reproducer triggers this by calling clone() with flags=0x80, resulting in exit_signal = (0x80 & CSIGNAL) = 128, which exceeds _NSIG and is not a valid signal. The v1 of this patch added the check only in the clone() syscall handler, which is incomplete. kernel_clone() has other callers such as sys_ia32_clone() which would remain unprotected. Move the check to kernel_clone() to cover all callers. Since the valid_signal() check is now in kernel_clone() and covers all callers including clone3(), the same check in copy_clone_args_from_user() becomes redundant and is removed. The higher 32bits check for clone3() is kept as it is clone3() specific. Note that this is a user-visible change: previously, passing an invalid exit_signal to clone() was silently accepted. The man page for clone() does not document any defined behavior for invalid exit_signal values, so rejecting them with -EINVAL is the correct behavior. It is unlikely that any sane application relies on passing an invalid exit_signal. [oleg@redhat.com: the comment above kernel_clone() should be updated] Link: https://lore.kernel.org/abwvgU17W8wuW2-J@redhat.com Link: https://lore.kernel.org/20260316151956.563558-1-kartikey406@gmail.com Fixes: 3f2c788a1314 ("fork: prevent accidental access to clone3 features") Signed-off-by: Deepanshu Kartikey Signed-off-by: Oleg Nesterov Reported-by: syzbot+bbe6b99feefc3a0842de@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=bbe6b99feefc3a0842de Tested-by: syzbot+bbe6b99feefc3a0842de@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/20260307064202.353405-1-kartikey406@gmail.com/T/ [v1] Link: https://lore.kernel.org/all/20260316104536.558108-1-kartikey406@gmail.com/T/ [v2] Acked-by: Oleg Nesterov Acked-by: Michal Hocko Cc: Ben Segall Cc: Christian Brauner Cc: David Hildenbrand Cc: Dietmar Eggemann Cc: Ingo Molnar Cc: Juri Lelli Cc: Kees Cook Cc: Liam Howlett Cc: Lorenzo Stoakes (Oracle) Cc: Mel Gorman Cc: Mike Rapoport Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Valentin Schneider Cc: Vincent Guittot Cc: Vlastimil Babka Cc: Tetsuo Handa Signed-off-by: Andrew Morton --- kernel/fork.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) --- a/kernel/fork.c~kernel-fork-validate-exit_signal-in-kernel_clone +++ a/kernel/fork.c @@ -2664,8 +2664,6 @@ struct task_struct *create_io_thread(int * * It copies the process, and if successful kick-starts * it and waits for it to finish using the VM if required. - * - * args->exit_signal is expected to be checked for sanity by the caller. */ pid_t kernel_clone(struct kernel_clone_args *args) { @@ -2700,6 +2698,9 @@ pid_t kernel_clone(struct kernel_clone_a (args->pidfd == args->parent_tid)) return -EINVAL; + if (!valid_signal(args->exit_signal)) + return -EINVAL; + /* * Determine whether and which event to report to ptracer. When * called from kernel_thread or CLONE_UNTRACED is explicitly @@ -2898,11 +2899,9 @@ static noinline int copy_clone_args_from return -EINVAL; /* - * Verify that higher 32bits of exit_signal are unset and that - * it is a valid signal + * Verify that higher 32bits of exit_signal are unset */ - if (unlikely((args.exit_signal & ~((u64)CSIGNAL)) || - !valid_signal(args.exit_signal))) + if (unlikely(args.exit_signal & ~((u64)CSIGNAL))) return -EINVAL; if ((args.flags & CLONE_INTO_CGROUP) && _