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Wed, 7 Oct 2020 19:04:19 +0000 (UTC) X-HE-Tag: silk91_4215fc1271d1 X-Filterd-Recvd-Size: 4964 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Wed, 7 Oct 2020 19:04:18 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5CCE12168B; Wed, 7 Oct 2020 19:04:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602097457; bh=llfxpknjIWXGV1PRIAQcxo2wu7p/kw/F31cAdH+5TX0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ldJJe2wFmBaoUuddH8wZ6oJe8RqDmpVZiKmohkPIlhwNvLm9ES6k+23YepXYyBN7q Fw83LTzq9fnC391wl9zmtQaY85gHpYkTQPYwUYBCWeonnWwRAIBcLlSyXAG3m7t3CI 7/ciqTmm3JQf8YwSaOg3J9geHKO4nIPGZ0LLTuU8= Date: Wed, 7 Oct 2020 12:04:16 -0700 From: Andrew Morton To: Miaohe Lin Cc: , Subject: Re: [PATCH] mm: mmap: Fix general protection fault in unlink_file_vma() Message-Id: <20201007120416.0e826cbb79da76ac9673b9d8@linux-foundation.org> In-Reply-To: <20200916090733.31427-1-linmiaohe@huawei.com> References: <20200916090733.31427-1-linmiaohe@huawei.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, 16 Sep 2020 05:07:33 -0400 Miaohe Lin wrote: > The syzbot reported the below general protection fault: > > general protection fault, probably for non-canonical address > 0xe00eeaee0000003b: 0000 [#1] PREEMPT SMP KASAN > KASAN: maybe wild-memory-access in range > [0x00777770000001d8-0x00777770000001df] > CPU: 1 PID: 10488 Comm: syz-executor721 Not tainted 5.9.0-rc3-syzkaller #0 > RIP: 0010:unlink_file_vma+0x57/0xb0 mm/mmap.c:164 > Code: 4c 8b a5 a0 00 00 00 4d 85 e4 74 4e e8 92 d7 cd ff 49 8d bc 24 > d8 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c > 02 00 75 3d 4d 8b b4 24 d8 01 00 00 4d 8d 6e 78 4c 89 ef e8 > RSP: 0018:ffffc9000ac0f9b0 EFLAGS: 00010202 > RAX: dffffc0000000000 RBX: ffff88800010ceb0 RCX: ffffffff81592421 > RDX: 000eeeee0000003b RSI: ffffffff81a6736e RDI: 00777770000001d8 > RBP: ffff88800010ceb0 R08: 0000000000000001 R09: ffff88801291a50f > R10: ffffed10025234a1 R11: 0000000000000001 R12: 0077777000000000 > R13: 00007f1eea0da000 R14: 00007f1eea0d9000 R15: 0000000000000000 > FS: 0000000000000000(0000) GS:ffff8880ae700000(0000) > knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f1eea11a9d0 CR3: 000000000007e000 CR4: 00000000001506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > free_pgtables+0x1b3/0x2f0 mm/memory.c:415 > exit_mmap+0x2c0/0x530 mm/mmap.c:3184 > __mmput+0x122/0x470 kernel/fork.c:1076 > mmput+0x53/0x60 kernel/fork.c:1097 > exit_mm kernel/exit.c:483 [inline] > do_exit+0xa8b/0x29f0 kernel/exit.c:793 > do_group_exit+0x125/0x310 kernel/exit.c:903 > get_signal+0x428/0x1f00 kernel/signal.c:2757 > arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811 > exit_to_user_mode_loop kernel/entry/common.c:136 [inline] > exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:167 > syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:242 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > It's because the ->mmap() callback can change vma->vm_file and fput the > original file. But the commit d70cec898324 ("mm: mmap: merge vma after > call_mmap() if possible") failed to catch this case and always fput() the > original file, hence add an extra fput(). > > ... > > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1815,7 +1815,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags, > NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX); > if (merge) { > - fput(file); > + /* ->mmap() can change vma->vm_file and fput the original file. So > + * fput the vma->vm_file here or we would add an extra fput for file > + * and cause general protection fault ultimately. > + */ > + fput(vma->vm_file); > vm_area_free(vma); > vma = merge; > /* Update vm_flags and possible addr to pick up the change. We don't What about the case where this code block does its `goto unmap_writable'? /* Once vma denies write, undo our temporary denial count */ if (file) { unmap_writable: if (vm_flags & VM_SHARED) mapping_unmap_writable(file->f_mapping); if (vm_flags & VM_DENYWRITE) allow_write_access(file); } file = vma->vm_file; is this using the correct file? I think it is, but please do check.