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 us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0ABEBC83F17 for ; Mon, 28 Aug 2023 06:46:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1693205176; h=from:from:sender:sender:reply-to:subject:subject: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:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=uYrIzdMzhxwGbjXbCOWjYCwycyE98eA+8WwJAoEGRj0=; b=ZnB8BaFR3dBIPCPPXGNwhnMwl2AbI79dKBU0qovK5Q+7WURJN0IkToKDRNzLSrvNgjxZBm kFTy8Vd56FZ+GvlLzADO5sLDy6lJZKogD381UJzvhDoM5G+dS/JL1K6mXP36JPGS3Csoxb iycfOcDUSf3PAvQJuhLaLO6c83FxbqE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-584-n4zX5wBHOAONnJxZUlpcAQ-1; Mon, 28 Aug 2023 02:46:11 -0400 X-MC-Unique: n4zX5wBHOAONnJxZUlpcAQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 64CCE185A78B; Mon, 28 Aug 2023 06:46:09 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com [10.30.29.100]) by smtp.corp.redhat.com (Postfix) with ESMTP id ED7642166B25; Mon, 28 Aug 2023 06:46:08 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (localhost [IPv6:::1]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id D29A019465B6; Mon, 28 Aug 2023 06:46:08 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id 3889119465A8 for ; Sat, 26 Aug 2023 02:29:17 +0000 (UTC) Received: by smtp.corp.redhat.com (Postfix) id EC3CD140E962; Sat, 26 Aug 2023 02:29:16 +0000 (UTC) Received: from mimecast-mx02.redhat.com (mimecast07.extmail.prod.ext.rdu2.redhat.com [10.11.55.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E4F10140E950 for ; Sat, 26 Aug 2023 02:29:16 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-1.mimecast.com [205.139.110.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8FB583C0252E for ; Sat, 26 Aug 2023 02:29:16 +0000 (UTC) Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-606-lRWZFOprMOOxmVvZKBndfA-1; Fri, 25 Aug 2023 22:29:14 -0400 X-MC-Unique: lRWZFOprMOOxmVvZKBndfA-1 Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1qZj2i-0010QB-1S; Sat, 26 Aug 2023 02:28:52 +0000 Date: Sat, 26 Aug 2023 03:28:52 +0100 From: Al Viro To: Jan Kara Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> MIME-Version: 1.0 In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 X-Mailman-Approved-At: Mon, 28 Aug 2023 06:46:05 +0000 Subject: Re: [dm-devel] [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dave Kleikamp , jfs-discussion@lists.sourceforge.net, "Darrick J. Wong" , linux-nvme@lists.infradead.org, Joseph Qi , dm-devel@redhat.com, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, Jack Wang , Alasdair Kergon , drbd-dev@lists.linbit.com, linux-s390@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org, Sergey Senozhatsky , Christoph Hellwig , xen-devel@lists.xenproject.org, Gao Xiang , Christian Borntraeger , Kent Overstreet , Sven Schnelle , linux-pm@vger.kernel.org, Mike Snitzer , Chao Yu , Joern Engel , reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Christian Brauner , David Sterba , Jaegeuk Kim , Trond Myklebust , Jens Axboe , linux-raid@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, Ted Tso , linux-mm@kvack.org, Song Liu , linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Minchan Kim , ocfs2-devel@oss.oracle.com, Anna Schumaker , linux-fsdevel@vger.kernel.org, "Md. Haris Iqbal" , Andrew Morton , linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: zeniv.linux.org.uk Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel 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 6A11EC83F17 for ; Sat, 26 Aug 2023 02:30:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231736AbjHZC3d (ORCPT ); Fri, 25 Aug 2023 22:29:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36580 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231722AbjHZC3E (ORCPT ); Fri, 25 Aug 2023 22:29:04 -0400 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59B41A8; Fri, 25 Aug 2023 19:29:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=mPm/qZCa7MWW4zdrpIjhXYeIS6 8cbIgOvCf/9Y6gIxhhuc7MbOClbX1o3H4gTlXLJmOpOyil1pufLmdD8oxm6VhlxB4x6C/OQmKz1OC 9Sg7eN60e8HGn0pn/DtWEZ2zi7uHlJyyQNolWeGdXQEgqn78/62UYsbUB8gsUgOw68YkPTd36+fo0 kPzizyM3mKJ55bukbV99w6F1Yx4exn0ELF0EHA2mn4TEClpd2hjjcTiwEbEGv+vsWkEq4IC7ejHjR rO8uE9/3ipL5VpLJjGdd7WJssIdQ5Tj/z+j2E3fQDWI0Qb9TMLDhfRhfBXk5sw2QK4rJI42xn3tDe SBJa1VHw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1qZj2i-0010QB-1S; Sat, 26 Aug 2023 02:28:52 +0000 Date: Sat, 26 Aug 2023 03:28:52 +0100 From: Al Viro To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, Christoph Hellwig , Alasdair Kergon , Andrew Morton , Anna Schumaker , Chao Yu , Christian Borntraeger , "Darrick J. Wong" , Dave Kleikamp , David Sterba , dm-devel@redhat.com, drbd-dev@lists.linbit.com, Gao Xiang , Jack Wang , Jaegeuk Kim , jfs-discussion@lists.sourceforge.net, Joern Engel , Joseph Qi , Kent Overstreet , linux-bcache@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org, linux-mtd@lists.infradead.org, linux-nfs@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pm@vger.kernel.org, linux-raid@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-xfs@vger.kernel.org, "Md. Haris Iqbal" , Mike Snitzer , Minchan Kim , ocfs2-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org, Sergey Senozhatsky , Song Liu , Sven Schnelle , target-devel@vger.kernel.org, Ted Tso , Trond Myklebust , xen-devel@lists.xenproject.org, Jens Axboe , Christian Brauner Subject: Re: [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-bcache@vger.kernel.org On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. 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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9659AC83F11 for ; Sat, 26 Aug 2023 02:29:51 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=linux.org.uk header.i=@linux.org.uk header.a=rsa-sha256 header.s=zeniv-20220401 header.b=mPm/qZCa; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4RXgl15h7pz3c33 for ; Sat, 26 Aug 2023 12:29:49 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=linux.org.uk header.i=@linux.org.uk header.a=rsa-sha256 header.s=zeniv-20220401 header.b=mPm/qZCa; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=ftp.linux.org.uk (client-ip=2a03:a000:7:0:5054:ff:fe1c:15ff; helo=zeniv.linux.org.uk; envelope-from=viro@ftp.linux.org.uk; receiver=lists.ozlabs.org) Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4RXgkr37xnz2yhZ for ; Sat, 26 Aug 2023 12:29:38 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=mPm/qZCa7MWW4zdrpIjhXYeIS6 8cbIgOvCf/9Y6gIxhhuc7MbOClbX1o3H4gTlXLJmOpOyil1pufLmdD8oxm6VhlxB4x6C/OQmKz1OC 9Sg7eN60e8HGn0pn/DtWEZ2zi7uHlJyyQNolWeGdXQEgqn78/62UYsbUB8gsUgOw68YkPTd36+fo0 kPzizyM3mKJ55bukbV99w6F1Yx4exn0ELF0EHA2mn4TEClpd2hjjcTiwEbEGv+vsWkEq4IC7ejHjR rO8uE9/3ipL5VpLJjGdd7WJssIdQ5Tj/z+j2E3fQDWI0Qb9TMLDhfRhfBXk5sw2QK4rJI42xn3tDe SBJa1VHw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1qZj2i-0010QB-1S; Sat, 26 Aug 2023 02:28:52 +0000 Date: Sat, 26 Aug 2023 03:28:52 +0100 From: Al Viro To: Jan Kara Subject: Re: [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dave Kleikamp , jfs-discussion@lists.sourceforge.net, "Darrick J. Wong" , linux-nvme@lists.infradead.org, Joseph Qi , dm-devel@redhat.com, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, Jack Wang , Alasdair Kergon , drbd-dev@lists.linbit.com, linux-s390@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org, Sergey Senozhatsky , Christoph Hellwig , xen-devel@lists.xenproject.org, Christian Borntraeger , Kent Overstreet , Sven Schnelle , linux-pm@vger.kernel.org, Mike Snitzer , Joern Engel , reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Christian Brauner , David Sterba , Jaegeuk Kim , Trond Myklebust , Jens Axboe , linux-raid@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, Ted Tso , linux-mm@kvack.org, Song Liu , linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Minchan Kim , ocfs2-devel@oss.oracle.com, Anna Schumaker , linux-fsdevel@vger.kernel.org, "Md. Haris Iqbal" , Andrew Morton , linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. 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 lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7CC9BC83F10 for ; Sat, 26 Aug 2023 02:29:31 +0000 (UTC) Received: from [127.0.0.1] (helo=sfs-ml-3.v29.lw.sourceforge.com) by sfs-ml-3.v29.lw.sourceforge.com with esmtp (Exim 4.95) (envelope-from ) id 1qZj3J-0003Yr-2g; Sat, 26 Aug 2023 02:29:29 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-3.v29.lw.sourceforge.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1qZj3H-0003Yd-U6; Sat, 26 Aug 2023 02:29:27 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=Sender:In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=RUj3D3g1rMvZg9deBGHzQ2kPXB 3Yw5MhAGQ4fth7Mqy08wuOsqp4JR1d2dkNymNPw90YU35ZyFeHvLP080kcHnpjrDcPZsCrYQn+Tw8 08QUBhmu4qbztyhwkhe8tqRChiZgpwVEEcocDF1wxIoHVGFdcpcuWU6ozA3sjk8A1UuQ=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=Sender:In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=eAhGt/AASeVUcQUASvvNqx/VgW DdS8zvi8eqAncxxCRvAmBeXggXZStJizSF/R5FxSGwVBeYmkkEMxTNzjRvt6jL66ZVu4ULTLRuhxs jYnpMhxYvLMPoFQy3dHCnE8hXZaT05slNFMi1LAEQ8zmX+5SnwVvmRgBz44zoL32YaUk=; Received: from zeniv.linux.org.uk ([62.89.141.173]) by sfi-mx-2.v28.lw.sourceforge.com with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.95) id 1qZj3E-0005DF-EV; Sat, 26 Aug 2023 02:29:27 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=mPm/qZCa7MWW4zdrpIjhXYeIS6 8cbIgOvCf/9Y6gIxhhuc7MbOClbX1o3H4gTlXLJmOpOyil1pufLmdD8oxm6VhlxB4x6C/OQmKz1OC 9Sg7eN60e8HGn0pn/DtWEZ2zi7uHlJyyQNolWeGdXQEgqn78/62UYsbUB8gsUgOw68YkPTd36+fo0 kPzizyM3mKJ55bukbV99w6F1Yx4exn0ELF0EHA2mn4TEClpd2hjjcTiwEbEGv+vsWkEq4IC7ejHjR rO8uE9/3ipL5VpLJjGdd7WJssIdQ5Tj/z+j2E3fQDWI0Qb9TMLDhfRhfBXk5sw2QK4rJI42xn3tDe SBJa1VHw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1qZj2i-0010QB-1S; Sat, 26 Aug 2023 02:28:52 +0000 Date: Sat, 26 Aug 2023 03:28:52 +0100 From: Al Viro To: Jan Kara Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> X-Headers-End: 1qZj3E-0005DF-EV Subject: Re: [f2fs-dev] [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dave Kleikamp , jfs-discussion@lists.sourceforge.net, "Darrick J. Wong" , linux-nvme@lists.infradead.org, Joseph Qi , dm-devel@redhat.com, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, Jack Wang , Alasdair Kergon , drbd-dev@lists.linbit.com, linux-s390@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org, Sergey Senozhatsky , Christoph Hellwig , xen-devel@lists.xenproject.org, Gao Xiang , Christian Borntraeger , Kent Overstreet , Sven Schnelle , linux-pm@vger.kernel.org, Mike Snitzer , Joern Engel , reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Christian Brauner , David Sterba , Jaegeuk Kim , Trond Myklebust , Jens Axboe , linux-raid@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, Ted Tso , linux-mm@kvack.org, Song Liu , linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Minchan Kim , ocfs2-devel@oss.oracle.com, Anna Schumaker , linux-fsdevel@vger.kernel.org, "Md. Haris Iqbal" , Andrew Morton , linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle Date: Sat, 26 Aug 2023 03:28:52 +0100 Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=mPm/qZCa7MWW4zdrpIjhXYeIS6 8cbIgOvCf/9Y6gIxhhuc7MbOClbX1o3H4gTlXLJmOpOyil1pufLmdD8oxm6VhlxB4x6C/OQmKz1OC 9Sg7eN60e8HGn0pn/DtWEZ2zi7uHlJyyQNolWeGdXQEgqn78/62UYsbUB8gsUgOw68YkPTd36+fo0 kPzizyM3mKJ55bukbV99w6F1Yx4exn0ELF0EHA2mn4TEClpd2hjjcTiwEbEGv+vsWkEq4IC7ejHjR rO8uE9/3ipL5VpLJjGdd7WJssIdQ5Tj/z+j2E3fQDWI0Qb9TMLDhfRhfBXk5sw2QK4rJI42xn3tDe SBJa1VHw==; Content-Disposition: inline In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: drbd-dev-bounces-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org Errors-To: drbd-dev-bounces-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org To: Jan Kara Cc: Dave Kleikamp , jfs-discussion-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, "Darrick J. Wong" , linux-nvme-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Joseph Qi , dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Jack Wang , Alasdair Kergon , drbd-dev-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org, linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Sergey Senozhatsky , Christoph Hellwig , xen-devel-GuqFBffKawtpuQazS67q72D2FQJk+8+b@public.gmane.org, Gao Xiang , Christian Borntraeger , Kent Overstreet , Sven Schnelle , linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mike Snitzer , Chao Yu , Joern Engel , reiserfs-devel-u79uwXL29TbrhsbdSgBK9A@public.gmane.org On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BD24DC83F11 for ; Sat, 26 Aug 2023 02:29:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=lUeDDfQU4otg9KGixbSyhZhriNDKE7BuPDkiH/uQF+o=; b=H8A3btyONXyqke 10/mO7/q+qQGaYi2vHPrtc/F13YbEVjGZZb30ooLeuw9CTz21gkP8Jcv0aA4aNie9d/lBZhFor7bL 9BrRSEdqwl9Ci5xzw55EJxQu2EKsM4RRro74kNcun2OlIdne77r9P1a9KEKSeKkK9dA6wDYPBPWR5 K7HPl7OBu9Bze6a/ySKo7nVNYmxih0A3nzZszpxes6RATZw0cMkOayDY5uMFv8ub+UKMzE6vtIwy4 BqJVn2nUuUOGZb0jK7skD9D3uG5Pyq2srWnyc1PS+iPmqGAO2BW966zxcNjKVA0wOwrWd0qvP+uUK rucBmjrQUe6h8KRekKTA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qZj3T-006Jm7-0e; Sat, 26 Aug 2023 02:29:39 +0000 Received: from zeniv.linux.org.uk ([2a03:a000:7:0:5054:ff:fe1c:15ff]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qZj3Q-006JlI-0d; Sat, 26 Aug 2023 02:29:37 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kRz17k12DLtH5ptlx3fiiancvtShyoQwDvuAAOUED4Y=; b=mPm/qZCa7MWW4zdrpIjhXYeIS6 8cbIgOvCf/9Y6gIxhhuc7MbOClbX1o3H4gTlXLJmOpOyil1pufLmdD8oxm6VhlxB4x6C/OQmKz1OC 9Sg7eN60e8HGn0pn/DtWEZ2zi7uHlJyyQNolWeGdXQEgqn78/62UYsbUB8gsUgOw68YkPTd36+fo0 kPzizyM3mKJ55bukbV99w6F1Yx4exn0ELF0EHA2mn4TEClpd2hjjcTiwEbEGv+vsWkEq4IC7ejHjR rO8uE9/3ipL5VpLJjGdd7WJssIdQ5Tj/z+j2E3fQDWI0Qb9TMLDhfRhfBXk5sw2QK4rJI42xn3tDe SBJa1VHw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1qZj2i-0010QB-1S; Sat, 26 Aug 2023 02:28:52 +0000 Date: Sat, 26 Aug 2023 03:28:52 +0100 From: Al Viro To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, Christoph Hellwig , Alasdair Kergon , Andrew Morton , Anna Schumaker , Chao Yu , Christian Borntraeger , "Darrick J. Wong" , Dave Kleikamp , David Sterba , dm-devel@redhat.com, drbd-dev@lists.linbit.com, Gao Xiang , Jack Wang , Jaegeuk Kim , jfs-discussion@lists.sourceforge.net, Joern Engel , Joseph Qi , Kent Overstreet , linux-bcache@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org, linux-mtd@lists.infradead.org, linux-nfs@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pm@vger.kernel.org, linux-raid@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-xfs@vger.kernel.org, "Md. Haris Iqbal" , Mike Snitzer , Minchan Kim , ocfs2-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org, Sergey Senozhatsky , Song Liu , Sven Schnelle , target-devel@vger.kernel.org, Ted Tso , Trond Myklebust , xen-devel@lists.xenproject.org, Jens Axboe , Christian Brauner Subject: Re: [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230825_192936_257066_6B0C97AB X-CRM114-Status: GOOD ( 29.31 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/ From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) by mail19.linbit.com (LINBIT Mail Daemon) with ESMTP id EF7A44252EE for ; Sat, 26 Aug 2023 04:29:14 +0200 (CEST) Date: Sat, 26 Aug 2023 03:28:52 +0100 From: Al Viro To: Jan Kara Message-ID: <20230826022852.GO3390869@ZenIV> References: <20230810171429.31759-1-jack@suse.cz> <20230825015843.GB95084@ZenIV> <20230825134756.o3wpq6bogndukn53@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230825134756.o3wpq6bogndukn53@quack3> Sender: Al Viro Cc: Dave Kleikamp , jfs-discussion@lists.sourceforge.net, "Darrick J. Wong" , linux-nvme@lists.infradead.org, Joseph Qi , dm-devel@redhat.com, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, Jack Wang , Alasdair Kergon , drbd-dev@lists.linbit.com, linux-s390@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org, Sergey Senozhatsky , Christoph Hellwig , xen-devel@lists.xenproject.org, Gao Xiang , Christian Borntraeger , Kent Overstreet , Sven Schnelle , linux-pm@vger.kernel.org, Mike Snitzer , Chao Yu , Joern Engel , reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Christian Brauner , David Sterba , Jaegeuk Kim , Trond Myklebust , Jens Axboe , linux-raid@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, Ted Tso , linux-mm@kvack.org, Song Liu , linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Minchan Kim , ocfs2-devel@oss.oracle.com, Anna Schumaker , linux-fsdevel@vger.kernel.org, "Md. Haris Iqbal" , Andrew Morton , linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Subject: Re: [Drbd-dev] [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle List-Id: "*Coordination* of development, patches, contributions -- *Questions* \(even to developers\) go to drbd-user, please." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy.