From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 412032E7373; Sun, 7 Jun 2026 10:13:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780827191; cv=none; b=IPYFo0DK2svtVRGFoLau9gPZCgG6JmayVhjJudrqygH9mh3Nrr91bWR0hht6G3eldDES3wbyHRi1iJItiSNxf/a13AaF5RgH5BDnQ/YP0FYJxjmvHrwp7gcjRIEh4TMWIYHCBNK9lZuRBlHVSBo8yfBIKwvPphh6aQri/1d2GWw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780827191; c=relaxed/simple; bh=oPuduuwlhZlC4luN+w41kKU9pGlcghiuy2GCt7Bkp9g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nxEBu9WaXYp27K18LjSlTofAisgfPMPug7wSRNehJDxi5079ML0cO+z4NCFBRQftcyPojGw+y6LAaNzeFrEo+L3Y8zc6NpAaL1IaWtH+YPrbMyLLqLO7Qf4InbE2nn5HO61F6WB2IQqafPQvWnAohvsHT43HSivEvTxOIoues4o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=DBC55Wjg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="DBC55Wjg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45DAD1F00893; Sun, 7 Jun 2026 10:13:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780827190; bh=kBR0+JIbSJhT0kOet8C0276a1sanOTtYNe5CeUOFKhE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=DBC55WjgyzdyTyuUrHm1I3w/techQMvl9R2reD30DN7rtZz2XNyJ39IHgSeG1bOdu ekiz92T93XSLB6+bPMQBrHskd8dso0Ccv0ypR2t6b1GyiGQACq75xCQzjvYbSS18qI 6ZLREA7HMHeP1J6VEh913SI1h61Bi/j6UGzlwELg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Deepanshu Kartikey , Oleg Nesterov , syzbot+bbe6b99feefc3a0842de@syzkaller.appspotmail.com, Michal Hocko , Ben Segall , Christian Brauner , David Hildenbrand , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Kees Cook , Liam Howlett , "Lorenzo Stoakes (Oracle)" , Mel Gorman , Mike Rapoport , Peter Zijlstra , Steven Rostedt , Suren Baghdasaryan , Valentin Schneider , Vincent Guittot , Vlastimil Babka , Tetsuo Handa , Andrew Morton , Sasha Levin Subject: [PATCH 6.12 030/307] kernel/fork: validate exit_signal in kernel_clone() Date: Sun, 7 Jun 2026 11:57:07 +0200 Message-ID: <20260607095728.764887196@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095727.647295505@linuxfoundation.org> References: <20260607095727.647295505@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Deepanshu Kartikey [ Upstream commit 09e7827e785729f391c8d46dc71becce70d296ab ] 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 Signed-off-by: Sasha Levin --- kernel/fork.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index c4955cffcb6f4e..1f306743832b3e 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2773,8 +2773,6 @@ struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node) * * 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) { @@ -2799,6 +2797,9 @@ pid_t kernel_clone(struct kernel_clone_args *args) (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 @@ -2999,11 +3000,9 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs, 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) && -- 2.53.0