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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4C756C47088 for ; Fri, 2 Dec 2022 16:33:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233839AbiLBQdh (ORCPT ); Fri, 2 Dec 2022 11:33:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56790 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233721AbiLBQdd (ORCPT ); Fri, 2 Dec 2022 11:33:33 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B34817B56D; Fri, 2 Dec 2022 08:33:31 -0800 (PST) Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 0FCC121C4A; Fri, 2 Dec 2022 16:33:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1669998810; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hIc9GGjidMLX67s74TxPgelqErquLYtaNNBhCjPFqvA=; b=MwBmd4I4d8KSktFz/t5PZovdXIqOQ5v2Zt6TQ0Df/7i7flVc8VMat/73irTERwEquJZWuM 6ijPzkGxOpuXdJKjN7nsix4C2kjRUJUHja2j8+Xu1AxemS131SQg6jiCLzSJhvxiOi/x1l g8T2TpH66VWCsQku07NdRlCazSFzJVA= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1669998810; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hIc9GGjidMLX67s74TxPgelqErquLYtaNNBhCjPFqvA=; b=Cv8NaFoZeePDhTQ0uNdRQTyG/d8lLH+uoet4DwRfwNTXpyWRbDGj0rorDax8+cPZeWkp9S l6KyAVGggKGciHBA== Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap1.suse-dmz.suse.de (Postfix) with ESMTPS id C423013644; Fri, 2 Dec 2022 16:33:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id KrwsL9koimPFLQAAGKfGzw (envelope-from ); Fri, 02 Dec 2022 16:33:29 +0000 Message-ID: Date: Fri, 2 Dec 2022 17:33:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH] mm: do not BUG_ON missing brk mapping, because userspace can unmap it Content-Language: en-US To: "Jason A. Donenfeld" , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Cc: "Liam R . Howlett" , Yu Zhao , Catalin Marinas , David Hildenbrand , David Howells , Davidlohr Bueso , Matthew Wilcox , SeongJae Park , Sven Schnelle , Will Deacon References: <20221202162724.2009-1-Jason@zx2c4.com> From: Vlastimil Babka In-Reply-To: <20221202162724.2009-1-Jason@zx2c4.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/2/22 17:27, Jason A. Donenfeld wrote: > The following program will trigger the BUG_ON that this patch removes, > because the user can munmap() mm->brk: > > #include > #include > #include > #include > > static void *brk_now(void) > { > return (void *)syscall(SYS_brk, 0); > } > > static void brk_set(void *b) > { > assert(syscall(SYS_brk, b) != -1); > } > > int main(int argc, char *argv[]) > { > void *b = brk_now(); > brk_set(b + 4096); > assert(munmap(b - 4096, 4096 * 2) == 0); > brk_set(b); > return 0; > } > > Compile that with musl, since glibc actually uses brk(), and then > execute it, and it'll hit this splat: > > kernel BUG at mm/mmap.c:229! > invalid opcode: 0000 [#1] PREEMPT SMP > CPU: 12 PID: 1379 Comm: a.out Tainted: G S U 6.1.0-rc7+ #419 > RIP: 0010:__do_sys_brk+0x2fc/0x340 > Code: 00 00 4c 89 ef e8 04 d3 fe ff eb 9a be 01 00 00 00 4c 89 ff e8 35 e0 fe ff e9 6e ff ff ff 4d 89 a7 20> > RSP: 0018:ffff888140bc7eb0 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: 00000000007e7000 RCX: ffff8881020fe000 > RDX: ffff8881020fe001 RSI: ffff8881955c9b00 RDI: ffff8881955c9b08 > RBP: 0000000000000000 R08: ffff8881955c9b00 R09: 00007ffc77844000 > R10: 0000000000000000 R11: 0000000000000001 R12: 00000000007e8000 > R13: 00000000007e8000 R14: 00000000007e7000 R15: ffff8881020fe000 > FS: 0000000000604298(0000) GS:ffff88901f700000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000603fe0 CR3: 000000015ba9a005 CR4: 0000000000770ee0 > PKRU: 55555554 > Call Trace: > > do_syscall_64+0x2b/0x50 > entry_SYSCALL_64_after_hwframe+0x46/0xb0 > RIP: 0033:0x400678 > Code: 10 4c 8d 41 08 4c 89 44 24 10 4c 8b 01 8b 4c 24 08 83 f9 2f 77 0a 4c 8d 4c 24 20 4c 01 c9 eb 05 48 8b> > RSP: 002b:00007ffc77863890 EFLAGS: 00000212 ORIG_RAX: 000000000000000c > RAX: ffffffffffffffda RBX: 000000000040031b RCX: 0000000000400678 > RDX: 00000000004006a1 RSI: 00000000007e6000 RDI: 00000000007e7000 > RBP: 00007ffc77863900 R08: 0000000000000000 R09: 00000000007e6000 > R10: 00007ffc77863930 R11: 0000000000000212 R12: 00007ffc77863978 > R13: 00007ffc77863988 R14: 0000000000000000 R15: 0000000000000000 > > > Instead, just error out if the original mapping has been removed. > > Fixes: 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()") That's 6.1-rc1 so probably fast track to Linus as we don't need to introduce such trivial local user DoS in 6.1, right? > Cc: Liam R. Howlett > Cc: Yu Zhao > Cc: Catalin Marinas > Cc: David Hildenbrand > Cc: David Howells > Cc: Davidlohr Bueso > Cc: Matthew Wilcox > Cc: SeongJae Park > Cc: Sven Schnelle > Cc: Vlastimil Babka > Cc: Will Deacon > Cc: Andrew Morton > Signed-off-by: Jason A. Donenfeld Acked-by: Vlastimil Babka > --- > mm/mmap.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index c3c5c1d6103d..f5a37fe9a19e 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -226,8 +226,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk) > /* Search one past newbrk */ > mas_set(&mas, newbrk); > brkvma = mas_find(&mas, oldbrk); > - BUG_ON(brkvma == NULL); > - if (brkvma->vm_start >= oldbrk) > + if (!brkvma || brkvma->vm_start >= oldbrk) > goto out; /* mapping intersects with an existing non-brk vma. */ > /* > * mm->brk must be protected by write mmap_lock.