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Mon, 20 Apr 2020 07:00:24 -0700 (PDT) Received: from localhost.localdomain ([194.230.155.102]) by smtp.gmail.com with ESMTPSA id p5sm1511446wrg.49.2020.04.20.07.00.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Apr 2020 07:00:23 -0700 (PDT) From: Emanuele Giuseppe Esposito Subject: Re: [PATCH 1/8] apparmor: just use vfs_kern_mount to make .null To: Luis Chamberlain , Goldwyn Rodrigues Cc: linux-nfs@vger.kernel.org, Paolo Bonzini , Jeremy Kerr , Arnd Bergmann , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Dennis Dalessandro , Mike Marciniszyn , Doug Ledford , Jason Gunthorpe , Frederic Barrat , Andrew Donnellan , Greg Kroah-Hartman , Robert Richter , "Manoj N. Kumar" , "Matthew R. Ochs" , Uma Krishnan , "James E.J. Bottomley" , "Martin K. Petersen" , Felipe Balbi , Alexander Viro , Ian Kent , Joel Becker , Christoph Hellwig , "Rafael J. Wysocki" , Matthew Garrett , Ard Biesheuvel , Miklos Szeredi , Mike Kravetz , Mark Fasheh , Joseph Qi , Alexey Dobriyan , Kees Cook , Iurii Zaikin , Anton Vorontsov , Colin Cross , Tony Luck , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh , Hugh Dickins , Andrew Morton , "J. Bruce Fields" , Chuck Lever , Trond Myklebust , Anna Schumaker , "David S. Miller" , Jakub Kicinski , James Morris , "Serge E. Hallyn" , John Johansen , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-scsi@vger.kernel.org, linux-usb@vger.kernel.org, linux-fsdevel@vger.kernel.org, autofs@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org References: <20200414124304.4470-1-eesposit@redhat.com> <20200414124304.4470-2-eesposit@redhat.com> <20200416064405.GP11244@42.do-not-panic.com> Message-ID: Date: Mon, 20 Apr 2020 16:00:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200416064405.GP11244@42.do-not-panic.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252; format=flowed 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 4/16/20 8:44 AM, Luis Chamberlain wrote: > On Tue, Apr 14, 2020 at 02:42:55PM +0200, Emanuele Giuseppe Esposito wrote: >> aa_mk_null_file is using simple_pin_fs/simple_release_fs with local >> variables as arguments, for what would amount to a simple >> vfs_kern_mount/mntput pair if everything was inlined. Just use >> the normal filesystem API since the reference counting is not needed >> here. > > *Why* is refcounting not needed here? The refcount is a local variable and is always 0 on entry and exit, so it is not necessary to have refcounting across function invocations, such as what simple_pin_fs and simple_release_fs provide. Thank you, Emanuele > > Luis > >> >> Signed-off-by: Emanuele Giuseppe Esposito >> --- >> security/apparmor/apparmorfs.c | 12 ++++++------ >> 1 file changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c >> index 280741fc0f5f..828bb1eb77ea 100644 >> --- a/security/apparmor/apparmorfs.c >> +++ b/security/apparmor/apparmorfs.c >> @@ -2525,14 +2525,14 @@ struct path aa_null; >> >> static int aa_mk_null_file(struct dentry *parent) >> { >> - struct vfsmount *mount = NULL; >> + struct file_system_type *type = parent->d_sb->s_type; >> + struct vfsmount *mount; >> struct dentry *dentry; >> struct inode *inode; >> - int count = 0; >> - int error = simple_pin_fs(parent->d_sb->s_type, &mount, &count); >> >> - if (error) >> - return error; >> + mount = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL); >> + if (IS_ERR(mount)) >> + return PTR_ERR(mount); >> >> inode_lock(d_inode(parent)); >> dentry = lookup_one_len(NULL_FILE_NAME, parent, strlen(NULL_FILE_NAME)); >> @@ -2561,7 +2561,7 @@ static int aa_mk_null_file(struct dentry *parent) >> dput(dentry); >> out: >> inode_unlock(d_inode(parent)); >> - simple_release_fs(&mount, &count); >> + mntput(mount); >> return error; >> } >> >> -- >> 2.25.2 >> >