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[89.243.172.161]) by smtp.gmail.com with ESMTPSA id s10-v6sm1214607wmf.15.2018.10.12.07.49.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 12 Oct 2018 07:49:51 -0700 (PDT) Subject: Re: [PATCH 31/34] vfs: syscall: Add fspick() to select a superblock for reconfiguration [ver #12] To: David Howells , viro@zeniv.linux.org.uk Cc: linux-api@vger.kernel.org, torvalds@linux-foundation.org, ebiederm@xmission.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@redhat.com References: <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> <153754766004.17872.9829232103614083565.stgit@warthog.procyon.org.uk> From: Alan Jenkins Message-ID: <9b8bf436-65de-13b9-0002-0479d11c18ca@gmail.com> Date: Fri, 12 Oct 2018 15:49:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <153754766004.17872.9829232103614083565.stgit@warthog.procyon.org.uk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/09/2018 17:34, David Howells wrote: > Provide an fspick() system call that can be used to pick an existing > mountpoint into an fs_context which can thereafter be used to reconfigure a > superblock (equivalent of the superblock side of -o remount). > > This looks like: > > int fd = fspick(AT_FDCWD, "/mnt", > FSPICK_CLOEXEC | FSPICK_NO_AUTOMOUNT); > fsconfig(fd, FSCONFIG_SET_FLAG, "intr", NULL, 0); > fsconfig(fd, FSCONFIG_SET_FLAG, "noac", NULL, 0); > fsconfig(fd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0); > > At the point of fspick being called, the file descriptor referring to the > filesystem context is in exactly the same state as the one that was created > by fsopen() after fsmount() has been successfully called. > > Signed-off-by: David Howells > cc: linux-api@vger.kernel.org > --- > > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > fs/fsopen.c | 54 ++++++++++++++++++++++++++++++++ > include/linux/syscalls.h | 1 + > include/uapi/linux/fs.h | 5 +++ > 5 files changed, 62 insertions(+) > > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl > index c78b68256f8a..d1eb6c815790 100644 > --- a/arch/x86/entry/syscalls/syscall_32.tbl > +++ b/arch/x86/entry/syscalls/syscall_32.tbl > @@ -403,3 +403,4 @@ > 389 i386 fsopen sys_fsopen __ia32_sys_fsopen > 390 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig > 391 i386 fsmount sys_fsmount __ia32_sys_fsmount > +392 i386 fspick sys_fspick __ia32_sys_fspick > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl > index d44ead5d4368..d3ab703c02bb 100644 > --- a/arch/x86/entry/syscalls/syscall_64.tbl > +++ b/arch/x86/entry/syscalls/syscall_64.tbl > @@ -348,6 +348,7 @@ > 337 common fsopen __x64_sys_fsopen > 338 common fsconfig __x64_sys_fsconfig > 339 common fsmount __x64_sys_fsmount > +340 common fspick __x64_sys_fspick > > # > # x32-specific system call numbers start at 512 to avoid cache impact > diff --git a/fs/fsopen.c b/fs/fsopen.c > index 5955a6b65596..9ead9220e2cb 100644 > --- a/fs/fsopen.c > +++ b/fs/fsopen.c > @@ -155,6 +155,60 @@ SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags) > return ret; > } > > +/* > + * Pick a superblock into a context for reconfiguration. > + */ > +SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags) > +{ > + struct fs_context *fc; > + struct path target; > + unsigned int lookup_flags; > + int ret; > + > + if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN)) > + return -EPERM; This seems to accept basically any mount.  Specifically: are you sure it's OK to return a handle to a SB_NO_USER superblock? # strace -f -v -e trace=154 \ ./fspick 3