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From: Aleksa Sarai <cyphar@cyphar.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jeff Layton <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Shuah Khan <shuah@kernel.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Christian Brauner <christian@brauner.io>,
	David Drysdale <drysdale@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Eric Biederman <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
	Tycho Andersen <tycho@tycho.ws>, Chanho Min <chanho.min@lge.com>,
	Oleg Nesterov <oleg@redhat.com>, Aleksa Sarai <asarai@suse.de>,
	containers@lists.linux-foundation.org,
	linux-alpha@vger.kernel.org, linux-api@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
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	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
	linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org
Subject: Re: [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags
Date: Fri, 12 Jul 2019 20:57:45 +1000
Message-ID: <20190712105745.nruaftgeat6irhzr@yavin> (raw)
In-Reply-To: <20190712043341.GI17978@ZenIV.linux.org.uk>

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On 2019-07-12, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Sun, Jul 07, 2019 at 12:57:32AM +1000, Aleksa Sarai wrote:
> > @@ -1442,8 +1464,11 @@ static int follow_dotdot_rcu(struct nameidata *nd)
> >  	struct inode *inode = nd->inode;
> >  
> >  	while (1) {
> > -		if (path_equal(&nd->path, &nd->root))
> > +		if (path_equal(&nd->path, &nd->root)) {
> > +			if (unlikely(nd->flags & LOOKUP_BENEATH))
> > +				return -EXDEV;
> 
> > @@ -1468,6 +1493,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
> >  				return -ECHILD;
> >  			if (&mparent->mnt == nd->path.mnt)
> >  				break;
> > +			if (unlikely(nd->flags & LOOKUP_XDEV))
> > +				return -EXDEV;
> >  			/* we know that mountpoint was pinned */
> >  			nd->path.dentry = mountpoint;
> >  			nd->path.mnt = &mparent->mnt;
> > @@ -1482,6 +1509,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
> >  			return -ECHILD;
> >  		if (!mounted)
> >  			break;
> > +		if (unlikely(nd->flags & LOOKUP_XDEV))
> > +			return -EXDEV;
> 
> Are you sure these failure exits in follow_dotdot_rcu() won't give
> suprious hard errors?

I could switch to -ECHILD for the *_rcu() checks if you'd prefer that.
Though, I'd have (probably naively) thought that you'd have already
gotten -ECHILD from the seqlock checks if there was a race during ".."
handling.

> > +	if (unlikely(nd->flags & LOOKUP_BENEATH)) {
> > +		error = dirfd_path_init(nd);
> > +		if (unlikely(error))
> > +			return ERR_PTR(error);
> > +		nd->root = nd->path;
> > +		if (!(nd->flags & LOOKUP_RCU))
> > +			path_get(&nd->root);
> > +	}
> >  	if (*s == '/') {
> >  		if (likely(!nd->root.mnt))
> >  			set_root(nd);
> > @@ -2350,9 +2400,11 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
> >  			s = ERR_PTR(error);
> >  		return s;
> >  	}
> > -	error = dirfd_path_init(nd);
> > -	if (unlikely(error))
> > -		return ERR_PTR(error);
> > +	if (likely(!nd->path.mnt)) {
> 
> Is that a weird way of saying "if we hadn't already called dirfd_path_init()"?

Yes. I did it to be more consistent with the other "have we got the
root" checks elsewhere. Is there another way you'd prefer I do it?

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-06 14:57 [PATCH v9 00/10] namei: openat2(2) path resolution restrictions Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 01/10] namei: obey trailing magic-link DAC permissions Aleksa Sarai
2019-07-12  4:14   ` Al Viro
2019-07-12  6:36     ` Al Viro
2019-07-12 12:20     ` Aleksa Sarai
2019-07-12 13:10       ` Al Viro
2019-07-14  7:11         ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 02/10] procfs: switch magic-link modes to be more sane Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 03/10] open: O_EMPTYPATH: procfs-less file descriptor re-opening Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 04/10] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2019-07-12  4:20   ` Al Viro
2019-07-12 12:07     ` Aleksa Sarai
2019-07-12 12:12       ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-07-12  4:33   ` Al Viro
2019-07-12 10:57     ` Aleksa Sarai [this message]
2019-07-12 12:39       ` Al Viro
2019-07-12 12:55         ` Al Viro
2019-07-12 13:25           ` Al Viro
2019-07-12 15:00             ` Al Viro
2019-07-13  2:41               ` Al Viro
2019-07-14  3:58                 ` Al Viro
2019-07-16  8:03                   ` Aleksa Sarai
2019-07-14  7:00                 ` Aleksa Sarai
2019-07-14 14:36                   ` Al Viro
2019-07-14 10:31             ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 06/10] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 07/10] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 08/10] open: openat2(2) syscall Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 09/10] kselftest: save-and-restore errno to allow for %m formatting Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 10/10] selftests: add openat2(2) selftests Aleksa Sarai
2019-07-08  1:15   ` Michael Ellerman
2019-07-08  5:47     ` Aleksa Sarai
2019-07-12 15:11 ` [PATCH v9 00/10] namei: openat2(2) path resolution restrictions Al Viro
2019-07-12 15:32   ` Aleksa Sarai

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