From: Al Viro <viro@zeniv.linux.org.uk>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: David Howells <dhowells@redhat.com>,
Eric Biederman <ebiederm@xmission.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
stable@vger.kernel.org,
Christian Brauner <christian.brauner@ubuntu.com>,
Serge Hallyn <serge@hallyn.com>,
dev@opencontainers.org, containers@lists.linux-foundation.org,
linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks
Date: Wed, 1 Jan 2020 03:08:15 +0000 [thread overview]
Message-ID: <20200101030815.GA17593@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200101005446.GH4203@ZenIV.linux.org.uk>
On Wed, Jan 01, 2020 at 12:54:46AM +0000, Al Viro wrote:
> Note, BTW, that lookup_last() (aka walk_component()) does just
> that - we only hit step_into() on LAST_NORM. The same goes
> for do_last(). mountpoint_last() not doing the same is _not_
> intentional - it's definitely a bug.
>
> Consider your testcase; link points to . here. So the only
> thing you could expect from trying to follow it would be
> the directory 'link' lives in. And you don't have it
> when you reach the fscker via /proc/self/fd/3; what happens
> instead is nd->path set to ./link (by nd_jump_link()) *AND*
> step_into() called, pushing the same ./link onto stack.
> It violates all kinds of assumptions made by fs/namei.c -
> when pushing a symlink onto stack nd->path is expected to
> contain the base directory for resolving it.
>
> I'm fairly sure that this is the cause of at least some
> of the insanity you've caught; there always could be
> something else, of course, but this hole needs to be
> closed in any case.
... and with removal of now unused local variable, that's
mountpoint_last(): fix the treatment of LAST_BIND
step_into() should be attempted only in LAST_NORM
case, when we have the parent directory (in nd->path).
We get away with that for LAST_DOT and LOST_DOTDOT,
since those can't be symlinks, making step_init() and
equivalent of path_to_nameidata() - we do a bit of
useless work, but that's it. For LAST_BIND (i.e.
the case when we'd just followed a procfs-style
symlink) we really can't go there - result might
be a symlink and we really can't attempt following
it.
lookup_last() and do_last() do handle that properly;
mountpoint_last() should do the same.
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/fs/namei.c b/fs/namei.c
index d6c91d1e88cb..13f9f973722b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2643,7 +2643,6 @@ EXPORT_SYMBOL(user_path_at_empty);
static int
mountpoint_last(struct nameidata *nd)
{
- int error = 0;
struct dentry *dir = nd->path.dentry;
struct path path;
@@ -2656,10 +2655,7 @@ mountpoint_last(struct nameidata *nd)
nd->flags &= ~LOOKUP_PARENT;
if (unlikely(nd->last_type != LAST_NORM)) {
- error = handle_dots(nd, nd->last_type);
- if (error)
- return error;
- path.dentry = dget(nd->path.dentry);
+ return handle_dots(nd, nd->last_type);
} else {
path.dentry = d_lookup(dir, &nd->last);
if (!path.dentry) {
next prev parent reply other threads:[~2020-01-01 3:08 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-30 5:20 [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Aleksa Sarai
2019-12-30 5:20 ` [PATCH RFC 1/1] " Aleksa Sarai
2019-12-30 7:34 ` Linus Torvalds
2019-12-30 8:28 ` Aleksa Sarai
2020-01-08 4:39 ` Andy Lutomirski
2019-12-30 5:44 ` [PATCH RFC 0/1] " Al Viro
2019-12-30 5:49 ` Aleksa Sarai
2019-12-30 7:29 ` Aleksa Sarai
2019-12-30 7:53 ` Linus Torvalds
2019-12-30 8:32 ` Aleksa Sarai
2020-01-02 8:58 ` David Laight
2020-01-02 9:09 ` Aleksa Sarai
2020-01-01 0:43 ` Al Viro
2020-01-01 0:54 ` Al Viro
2020-01-01 3:08 ` Al Viro [this message]
2020-01-01 14:44 ` Aleksa Sarai
2020-01-01 23:40 ` Al Viro
2020-01-02 3:59 ` Aleksa Sarai
2020-01-03 1:49 ` Al Viro
2020-01-04 4:46 ` Ian Kent
2020-01-08 3:13 ` Al Viro
2020-01-08 3:54 ` Linus Torvalds
2020-01-08 21:34 ` Al Viro
2020-01-10 0:08 ` Linus Torvalds
2020-01-10 4:15 ` Al Viro
2020-01-10 5:03 ` Linus Torvalds
2020-01-10 6:20 ` Ian Kent
2020-01-12 21:33 ` Al Viro
2020-01-13 2:59 ` Ian Kent
2020-01-14 0:25 ` Ian Kent
2020-01-14 4:39 ` Al Viro
2020-01-14 5:01 ` Ian Kent
2020-01-14 5:59 ` Ian Kent
2020-01-10 21:07 ` Aleksa Sarai
2020-01-14 4:57 ` Al Viro
2020-01-14 5:12 ` Al Viro
2020-01-14 20:01 ` Aleksa Sarai
2020-01-15 14:25 ` Al Viro
2020-01-15 14:29 ` Aleksa Sarai
2020-01-15 14:34 ` Aleksa Sarai
2020-01-15 14:48 ` Al Viro
2020-01-15 13:57 ` Aleksa Sarai
2020-01-19 3:14 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes Al Viro
2020-01-19 14:33 ` Ian Kent
2020-01-10 23:19 ` [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Al Viro
2020-01-13 1:48 ` Ian Kent
2020-01-13 3:54 ` Al Viro
2020-01-13 6:00 ` Ian Kent
2020-01-13 6:03 ` Ian Kent
2020-01-13 13:30 ` Al Viro
2020-01-14 7:25 ` Ian Kent
2020-01-14 12:17 ` Ian Kent
2020-01-04 5:52 ` Andy Lutomirski
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