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 09D9B8BEE for ; Thu, 13 Feb 2025 00:18:21 +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=1739405902; cv=none; b=lQQVWTXckJq4VMQr6aiPjOSccLbU7ud1UtAKnj1P93cL5PS5u/VU9mSwEe2dVh3QWMZGU3XWNevxjblB9baYF7g7gm9+ysNk3/hEPFBhCSe4gNqtVstx61iWyi3Bo4aLgNfHsfhfZlRqTTi48vhtEfVT/WeJbCRh5Vm23lE6qaQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739405902; c=relaxed/simple; bh=rBKFdICfXC//TwPhUjStYFCCOyfQfVVxwoSt87pnLR4=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=oMXzCzrZvV6ve+FCJr7L6V8p/Aq7gyx9XcfriRzGt+e1uSWsrYiZfHA+F/k+u18ZfALweC3ECJCzdbJUF0j8uUxzVUxePFsLaI3tXRe0Fzjpeux3eeYJemreGhUWXAku/asTsz4u40gsD1wym0S8YBUeMJ7vGtJvn5sQ3FTh04Q= 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=J8sW0qAH; 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="J8sW0qAH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28F34C4CEDF; Thu, 13 Feb 2025 00:18:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1739405901; bh=rBKFdICfXC//TwPhUjStYFCCOyfQfVVxwoSt87pnLR4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=J8sW0qAHXhdqY4iL/ynVFTbeSGqS9ioHNlMnvu2nWpe0KjAOPlzzBTOvRxBivgynl G+FfSFosVTYJsSOF4w6AxXZS3Dr94f78mNmDigm7eLKpQxVfFcTMXAXS/SkYlL7TZl JEKEbHnmK4P5o9sN6glDHNE5xfmyrb5ZKiJVhwZo= Date: Wed, 12 Feb 2025 16:18:20 -0800 From: Andrew Morton To: gaoxu Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "Suren Baghdasaryan" , Barry Song <21cnbao@gmail.com>, yipengxiang , Hugh Dickins , Chris Li Subject: Re: [PATCH] mm: Fix possible NULL pointer dereference in __swap_duplicate Message-Id: <20250212161820.4fda79a3333d2345b60cef72@linux-foundation.org> In-Reply-To: <44655569e3a1419f800952004f07e714@honor.com> References: <44655569e3a1419f800952004f07e714@honor.com> 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=UTF-8 Content-Transfer-Encoding: 8bit On Wed, 12 Feb 2025 03:13:46 +0000 gaoxu wrote: > swp_swap_info() may return null; it is necessary to check the return value > to avoid NULL pointer dereference. The code for other calls to > swp_swap_info() includes checks, and __swap_duplicate() should also > include checks. Actually very few of the swp_swap_info() callers check for a NULL return. > The reason why swp_swap_info() returns NULL is unclear; it may be due to > CPU cache issues or DDR bit flips. Quite possibly it's a kernel bug. > The probability of this issue is very > small, and the stack info we encountered is as follows： > Unable to handle kernel NULL pointer dereference at virtual address > 0000000000000058 > > ... > > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3521,6 +3521,8 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) > int err, i; > > si = swp_swap_info(entry); > + if (unlikely(!si)) > + return -EINVAL; > > offset = swp_offset(entry); > VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); OK, I guess avoiding the crash is good. But please let's include a WARN so that we can perhaps fix the bug, if one is there.