Patch "fix d_walk()/non-delayed __d_free() race" has been added to the 3.14-stable tree

Patch "fix d_walk()/non-delayed __d_free() race" has been added to the 3.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    fix d_walk()/non-delayed __d_free() race

to the 3.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fix-d_walk-non-delayed-__d_free-race.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 7 Jun 2016 21:26:55 -0400
Subject: fix d_walk()/non-delayed __d_free() race

From: Al Viro <viro@zeniv.linux.org.uk>

commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream.

Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay.  Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.

Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover.  Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/dcache.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1500,7 +1500,7 @@ struct dentry *d_alloc(struct dentry * p
 	struct dentry *dentry = __d_alloc(parent->d_sb, name);
 	if (!dentry)
 		return NULL;
-
+	dentry->d_flags |= DCACHE_RCUACCESS;
 	spin_lock(&parent->d_lock);
 	/*
 	 * don't need child lock because it is not subject
@@ -2352,7 +2352,6 @@ static void __d_rehash(struct dentry * e
 {
 	BUG_ON(!d_unhashed(entry));
 	hlist_bl_lock(b);
-	entry->d_flags |= DCACHE_RCUACCESS;
 	hlist_bl_add_head_rcu(&entry->d_hash, b);
 	hlist_bl_unlock(b);
 }
@@ -2536,6 +2535,7 @@ static void __d_move(struct dentry * den
 
 	/* ... and switch the parents */
 	if (IS_ROOT(dentry)) {
+		dentry->d_flags |= DCACHE_RCUACCESS;
 		dentry->d_parent = target->d_parent;
 		target->d_parent = target;
 		INIT_LIST_HEAD(&target->d_child);


Patches currently in stable-queue which might be from viro@zeniv.linux.org.uk are

queue-3.14/fix-d_walk-non-delayed-__d_free-race.patch

Patch "fix d_walk()/non-delayed __d_free() race" has been added to the 3.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    fix d_walk()/non-delayed __d_free() race

to the 3.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fix-d_walk-non-delayed-__d_free-race.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From w@1wt.eu  Fri Sep  9 16:26:43 2016
From: Willy Tarreau <w@1wt.eu>
Date: Sat, 27 Aug 2016 11:31:35 +0200
Subject: fix d_walk()/non-delayed __d_free() race
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jslaby@suse.cz>
Cc: Jari Ruusu <jariruusu@users.sourceforge.net>, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>, Ben Hutchings <ben@decadent.org.uk>
Message-ID: <20160827093135.GA28378@1wt.eu>
Content-Disposition: inline

From: Willy Tarreau <w@1wt.eu>

I checked Jari's explanation below and found that v3.14.77 and v3.12.62
are missing the same fix as 3.10. In fact Al's original commit 3d56c25
("fix d_walk()/non-delayed __d_free() race") used to mention to check 
this __d_materialise_dentry() function in the Cc: stable line, but this
got lost during the backports.

Normally all of our 3 kernels need to apply the following patch that
Ben correctly put in 3.16 and 3.2. I'm fixing the backport in 3.10.103
right now.

On Mon, Aug 22, 2016 at 04:56:57PM +0300, Jari Ruusu wrote:
> This patch for 3.10 branch appears to be missing one important
> 
> +       dentry->d_flags |= DCACHE_RCUACCESS;
> 
> in fs/dcache.c __d_materialise_dentry() function. When Ben Hutchings
> backported Al Viro's original fix to stable branches that he maintains,
> he added that one additional line to both 3.2 and 3.16 branches. Please
> consider including that additional one line fix for 3.10 stable branch
> also.
> 
> 
> Ben Hutchings said this on his 3.2.82-rc1 patch:
> [bwh: Backported to 3.2:
>  - Adjust context
>  - Also set the flag in __d_materialise_dentry())]
> 
> http://marc.info/?l=linux-kernel&m=147117565612275&w=2
> 
> 
> Ben Hutchings said this on his 3.16.37-rc1 patch:
> [bwh: Backported to 3.16:
>  - Adjust context
>  - Also set the flag in __d_materialise_dentry())]
> 
> http://marc.info/?l=linux-kernel&m=147117433412006&w=2
> 
> 
> Also mentioned by Sasha Levin on 3.18 and 4.1 commits:
> Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry())
> 
> http://marc.info/?l=linux-stable-commits&m=146648034410827&w=2
> http://marc.info/?l=linux-stable-commits&m=146647471009771&w=2


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/dcache.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2652,6 +2652,7 @@ static void __d_materialise_dentry(struc
 	switch_names(dentry, anon);
 	swap(dentry->d_name.hash, anon->d_name.hash);
 
+	dentry->d_flags |= DCACHE_RCUACCESS;
 	dentry->d_parent = dentry;
 	list_del_init(&dentry->d_child);
 	anon->d_parent = dparent;


Patches currently in stable-queue which might be from w@1wt.eu are

queue-3.14/fix-d_walk-non-delayed-__d_free-race.patch
queue-3.14/hid-hid-input-add-parentheses-to-quell-gcc-warning.patch
queue-3.14/revert-can-fix-handling-of-unmodifiable-configuration-options-fix.patch
queue-3.14/be2iscsi-fix-bogus-warn_on-length-check.patch
queue-3.14/stb6100-fix-buffer-length-check-in-stb6100_write_reg_range.patch
queue-3.14/alsa-oxygen-fix-logical-not-parentheses-warning.patch