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 DEB203E3165 for ; Mon, 24 Aug 2026 10:56:53 +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=1787569015; cv=none; b=Lh4tELdYME0HrFo1TcFYmF0w7tx8RDGUJKzrLT2/J+0wkGKcVsWEYWXWPQW5iJu2bKS4vQDxaSiKbyrXmYCtB+X6W5x0OyLc3CYXiFg/e9zfqyQnJTmhCMFTxO8Dc+QyulgSw8Bf4SghwRqF9S3P5pFO7ZNCyL6DfU9hTzZ8acE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787569015; c=relaxed/simple; bh=jBQZUtYMSdYdGc9j/057+vyrLOqphjxGvHtWmoEFN+E=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=alGXhL19qzESHG2cJxYPe5TCoUPrvEUcn31D1o0PCuwSVUAlRH/CrGIWzZ6Z+tD1yZ0UiKOc0R6kTNv6zqeB4299upVohwEBiU0Oa+Y1ETVp4S16upZxuYBGK16nu0Kr1MIDyaYjHaSsc3PBEV0Ud2xUf0D/yakOiIaDvsttA1k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=lEzssSKP; 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="lEzssSKP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 112061F000E9; Mon, 24 Aug 2026 10:56:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787569013; bh=VPVI4cKcOdRTXrTJwrHXhaM7lW5LKmJhOg1WudkADYM=; h=Subject:To:Cc:From:Date; b=lEzssSKPhYjC0GSjTQVz/2ofNur9nxHsamoktqIUXlbdkX/GfqsuZE5gVKpqT4097 5uJnMWJmcBkqQWMOZXMa6BnY8t17qnZM2yUQkz1xnC2ODgjF29PmpaoSqCJs/FW5bs ze/EjMLdXAeTXXEKit0htdqFj951EFhad7J9sYV4= Subject: FAILED: patch "[PATCH] futex/pi: Reject cross-mm private futex owners" failed to apply to 7.1-stable tree To: kylebot@openai.com,peterz@infradead.org,tglx@kernel.org Cc: From: Date: Mon, 24 Aug 2026 12:56:46 +0200 Message-ID: <2026082446-lumpish-subdivide-9766@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 7.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.1.y git checkout FETCH_HEAD git cherry-pick -x 59b3732f95dda1fbd2234514d35f4fb6b5bb6d85 # git commit -s git send-email --to '' --in-reply-to '2026082446-lumpish-subdivide-9766@gregkh' --subject-prefix 'PATCH 7.1.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 59b3732f95dda1fbd2234514d35f4fb6b5bb6d85 Mon Sep 17 00:00:00 2001 From: Kyle Zeng Date: Fri, 7 Aug 2026 17:07:03 +0200 Subject: [PATCH] futex/pi: Reject cross-mm private futex owners A private futex key borrows the waiter's mm without taking an mm_users reference. Nevertheless, attach_to_pi_owner() currently accepts an owner from a different address space and copies the private key into the owner's PI state. When that owner exits, exit_pi_state_list() uses the saved key to find the hash bucket and acquires a reference to the waiter's private hash. If the last user of the waiter's mm exits concurrently, futex_hash_free() frees the hash while the owner still uses its bucket and reference. Prevent this by validating in attach_to_pi_owner() that, for private futexes, the owner mm and waiter mm are the same. Perform the check with the owner's pi_lock held and after validating owner::futex::state to serialize against a concurrent PI-state exit cleanup. [ tglx: Amended comment ] Fixes: 80367ad01d93 ("futex: Add basic infrastructure for local task local hash") Signed-off-by: Kyle Zeng Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Assisted-by: Codex:gpt-5.6-sol Cc: stable@vger.kernel.org diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c index 795011ea1202..3e277ef155cd 100644 --- a/kernel/futex/pi.c +++ b/kernel/futex/pi.c @@ -465,6 +465,26 @@ static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key, return ret; } + /* + * If the owner is about to exit() or exec() and tries to modify + * p::futex::exit_state it is serialized against this code by + * p::pi_lock. + */ + if (IS_ENABLED(CONFIG_MMU) && futex_key_is_private(key)) { + /* + * A private futex key holds a pointer to the waiter's mm + * without holding a reference on it. So it must not be attached + * to an owner in a different address space. Otherwise that + * owner's exit cleanup could access the private hash after the + * key's mm is freed. + */ + if (unlikely(p->mm != key->private.mm)) { + raw_spin_unlock_irq(&p->pi_lock); + put_task_struct(p); + return -EPERM; + } + } + __attach_to_pi_owner(p, key, ps); raw_spin_unlock_irq(&p->pi_lock);