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Biederman" Cc: linux-kernel@vger.kernel.org, Al Viro , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Kees Cook , Oleg Nesterov , Alexey Gladkov , Linus Torvalds , Jeff Dike , Richard Weinberger , Anton Ivanov Subject: Re: [PATCH 2/3] uml: Create a private mount of proc for mconsole Message-ID: <20200228203058.jcnqeyvmqhfslcym@wittgenstein> References: <20200212203833.GQ23230@ZenIV.linux.org.uk> <20200212204124.GR23230@ZenIV.linux.org.uk> <87lfp7h422.fsf@x220.int.ebiederm.org> <87pnejf6fz.fsf@x220.int.ebiederm.org> <871rqpaswu.fsf_-_@x220.int.ebiederm.org> <871rqk2brn.fsf_-_@x220.int.ebiederm.org> <878skmsbyy.fsf_-_@x220.int.ebiederm.org> <87wo86qxcs.fsf_-_@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87wo86qxcs.fsf_-_@x220.int.ebiederm.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 28, 2020 at 02:18:43PM -0600, Eric W. Biederman wrote: > > The mconsole code only ever accesses proc for the initial pid > namespace. Instead of depending upon the proc_mnt which is > for proc_flush_task have uml create it's own mount of proc > instead. > > This allows proc_flush_task to evolve and remove the > need for having a proc_mnt to do it's job. > > Cc: Jeff Dike > Cc: Richard Weinberger > Cc: Anton Ivanov > Signed-off-by: Eric W. Biederman > --- > arch/um/drivers/mconsole_kern.c | 28 +++++++++++++++++++++++++++- > 1 file changed, 27 insertions(+), 1 deletion(-) > > diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c > index e8f5c81c2c6c..30575bd92975 100644 > --- a/arch/um/drivers/mconsole_kern.c > +++ b/arch/um/drivers/mconsole_kern.c > @@ -36,6 +36,8 @@ > #include "mconsole_kern.h" > #include > > +static struct vfsmount *proc_mnt = NULL; > + > static int do_unlink_socket(struct notifier_block *notifier, > unsigned long what, void *data) > { > @@ -123,7 +125,7 @@ void mconsole_log(struct mc_request *req) > > void mconsole_proc(struct mc_request *req) > { > - struct vfsmount *mnt = init_pid_ns.proc_mnt; > + struct vfsmount *mnt = proc_mnt; > char *buf; > int len; > struct file *file; > @@ -134,6 +136,10 @@ void mconsole_proc(struct mc_request *req) > ptr += strlen("proc"); > ptr = skip_spaces(ptr); > > + if (!mnt) { > + mconsole_reply(req, "Proc not available", 1, 0); > + goto out; > + } > file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY, 0); > if (IS_ERR(file)) { > mconsole_reply(req, "Failed to open file", 1, 0); > @@ -683,6 +689,24 @@ void mconsole_stack(struct mc_request *req) > with_console(req, stack_proc, to); > } > > +static int __init mount_proc(void) > +{ > + struct file_system_type *proc_fs_type; > + struct vfsmount *mnt; > + > + proc_fs_type = get_fs_type("proc"); > + if (!proc_fs_type) > + return -ENODEV; > + > + mnt = kern_mount(proc_fs_type); > + put_filesystem(proc_fs_type); > + if (IS_ERR(mnt)) > + return PTR_ERR(mnt); > + > + proc_mnt = mnt; > + return 0; > +} > + > /* > * Changed by mconsole_setup, which is __setup, and called before SMP is > * active. > @@ -696,6 +720,8 @@ static int __init mconsole_init(void) > int err; > char file[UNIX_PATH_MAX]; > > + mount_proc(); Hm, either check the return value or make the mount_proc() void? Probably worth logging something but moving on without proc. I guess this is user visible in some scenarios but the patch series seems worth it! Christian