From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 309A5C433EF for ; Thu, 10 Feb 2022 03:48:13 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9A75F6B0075; Wed, 9 Feb 2022 22:48:12 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 957116B007B; Wed, 9 Feb 2022 22:48:12 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7F7C56B007D; Wed, 9 Feb 2022 22:48:12 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0190.hostedemail.com [216.40.44.190]) by kanga.kvack.org (Postfix) with ESMTP id 7126F6B0075 for ; Wed, 9 Feb 2022 22:48:12 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 334898249980 for ; Thu, 10 Feb 2022 03:48:12 +0000 (UTC) X-FDA: 79125487224.19.FFCA69C Received: from mail-yb1-f175.google.com (mail-yb1-f175.google.com [209.85.219.175]) by imf28.hostedemail.com (Postfix) with ESMTP id BF5FBC0007 for ; Thu, 10 Feb 2022 03:48:11 +0000 (UTC) Received: by mail-yb1-f175.google.com with SMTP id v186so11818166ybg.1 for ; Wed, 09 Feb 2022 19:48:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=26LO++sGAEnTrwKspX8n5Js8aWWNBWjvhQH2G4UOuEk=; b=IWeHuyEeM7OuKImnXneHzgU17gcnqFrU5iCu5eOISxvZLLBhV10wT7a1MePqcRlmjK SwuqjEskw7pxo2CSZl25lFYMm+0s/Ys86uSty58yyVvoXrNahwbsZ1ZGzjjz0tE2IHVr 4tlXhC+4EVRVCNS5yptxw7/W9QUlF0yi9KNy40Cd5ux9eOHz+BLvzpptdjuDtsfSNUgy MRHYJKUXENVm2l1UKDZaP3aU3D3jXZA7hmYVX1nYTHmMHZWrVejicsICXXeuSwTQZ6+B pEJWrTxXpw2BzdvF9+EjGKoLT+zhaH5RmY82EkjmtBl6QMxqzKUiXu0ycO+D2zxq0j5C ENDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=26LO++sGAEnTrwKspX8n5Js8aWWNBWjvhQH2G4UOuEk=; b=H7WHC1cDBwjA3rhv/9//hiAHWPcSUGk/WMzjKW7lndwWiwjRNBzitVmrfJ46dNjHp3 lMOqYfZ/aZmIGWFpxC/VWAHqCF8lpbYtbqGiwCqOkMBknVsgeDBNfzKqboyUCJ4AlQoi sBuEasVZgrisLq2xD3zXLkVCwOvdXDZ9pTyn6nZfocpNHN6Kj/++MNHyJ2qB101jvHg2 CIx7IJZmGnCqQKido/lYjw77SHqwvmY9Lk8bGIWD+0MmqVwN238t60/0J8ECyaYtYAmc N5WINRjFeYKcHYsQqsk+geYpnco4B88KTjff7S4vaS2a6zrkR9ruWaC08NQDrL4awsgc +mbw== X-Gm-Message-State: AOAM533cE2zuic8rsxSCqLK9WZMyOxKgnrYQEH8N0IExVjeVIY4mzaNw 1mUvxsbp/n+25oX4qDBtAlAnREkN6E4PuoH9jktV5Q== X-Google-Smtp-Source: ABdhPJyhUAlXJoHLTcBJeZuXXmfwkIZnZvG4WVjC5LGwQnh+ocuYXOT6N3BMEltPCn7e4kZ43QvPOgO50id2WDMrNys= X-Received: by 2002:a25:cb02:: with SMTP id b2mr5508689ybg.243.1644464890859; Wed, 09 Feb 2022 19:48:10 -0800 (PST) MIME-Version: 1.0 References: <20220210001801.15413-1-surenb@google.com> <20220209163324.bbf26e7462b217d453c5a34f@linux-foundation.org> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 9 Feb 2022 19:48:00 -0800 Message-ID: Subject: Re: [PATCH 1/1] mm: Fix UAF when anon vma name is used after vma is freed To: Andrew Morton Cc: Colin Cross , Sumit Semwal , Michal Hocko , Dave Hansen , Kees Cook , Matthew Wilcox , "Kirill A . Shutemov" , Vlastimil Babka , Johannes Weiner , "Eric W. Biederman" , brauner@kernel.org, legion@kernel.org, ran.xiaokai@zte.com.cn, sashal@kernel.org, Chris Hyser , Davidlohr Bueso , Peter Collingbourne , caoxiaofeng@yulong.com, David Hildenbrand , Cyrill Gorcunov , linux-mm , LKML , kernel-team , syzbot+aa7b3d4b35f9dc46a366@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: z47jgartnycz6u5j8k7zzduiqpuzaqwb Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=IWeHuyEe; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf28.hostedemail.com: domain of surenb@google.com designates 209.85.219.175 as permitted sender) smtp.mailfrom=surenb@google.com X-Rspamd-Queue-Id: BF5FBC0007 X-HE-Tag: 1644464891-839525 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: . . On Wed, Feb 9, 2022 at 5:02 PM Suren Baghdasaryan wrote: > > On Wed, Feb 9, 2022 at 4:33 PM Andrew Morton wrote: > > > > On Wed, 9 Feb 2022 16:18:01 -0800 Suren Baghdasaryan wrote: > > > > > When adjacent vmas are being merged it can result in the vma that was > > > originally passed to madvise_update_vma being destroyed. In the current > > > implementation, the name parameter passed to madvise_update_vma points > > > directly to vma->anon_name->name and it is used after the call to > > > vma_merge. In the cases when vma_merge merges the original vma and > > > destroys it, this will result in use-after-free bug as shown below: > > > > > > madvise_vma_behavior << passes vma->anon_name->name as name param > > > madvise_update_vma(name) > > > vma_merge > > > __vma_adjust > > > vm_area_free <-- frees the vma > > > replace_vma_anon_name(name) <-- UAF > > > > > > Fix this by passing madvise_update_vma a copy of the name. > > > > > > ... > > > > > > --- a/kernel/sys.c > > > +++ b/kernel/sys.c > > > @@ -2263,7 +2263,6 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struct *t, unsigned long which, > > > > > > #ifdef CONFIG_ANON_VMA_NAME > > > > > > -#define ANON_VMA_NAME_MAX_LEN 80 > > > #define ANON_VMA_NAME_INVALID_CHARS "\\`$[]" > > > > > > static inline bool is_valid_name_char(char ch) > > > diff --git a/mm/madvise.c b/mm/madvise.c > > > index 5604064df464..f36a5a9942d8 100644 > > > --- a/mm/madvise.c > > > +++ b/mm/madvise.c > > > @@ -976,6 +976,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, > > > { > > > int error; > > > unsigned long new_flags = vma->vm_flags; > > > + char name_buf[ANON_VMA_NAME_MAX_LEN]; > > > + const char *anon_name; > > > > > > switch (behavior) { > > > case MADV_REMOVE: > > > @@ -1040,8 +1042,18 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, > > > break; > > > } > > > > > > + anon_name = vma_anon_name(vma); > > > + if (anon_name) { > > > + /* > > > + * Make a copy of the name because vma might be destroyed when > > > + * merged with another one and the name parameter might be used > > > + * after that. > > > + */ > > > + strcpy(name_buf, anon_name); > > > + anon_name = name_buf; > > > + } > > > error = madvise_update_vma(vma, prev, start, end, new_flags, > > > - vma_anon_name(vma)); > > > + anon_name); > > > > anon_name is refcounted. Why not use kref_get()/kref_put() instead of > > taking a copy? > > Yes, I considered that. It would require new get/put APIs for > anon_name and I thought I better keep it simple. This path is used > only by madvise() syscall, so the copy overhead should not be > critical. But if you think refcounting is more appropriate here I'll > happily rework it. It should still be quite simple. Please let me > know. On second thought, we might have more places in the future we need to stabilize anon_name, so put/get API can be useful. After prototyping the refcounting approach it looks simple enough to use instead of copying. Let me test it a bit and I'll post a replacement patch for this one tomorrow. Thanks, Suren. > > >