From linux-fsdevel-owner@vger.kernel.org Thu Nov 18 21:03:11 2010

From:	Josef Bacik <josef@redhat.com>

To:	linux-fsdevel@vger.kernel.org, eparis@redhat.com,

	linux-kernel@vger.kernel.org, sds@tycho.nsa.gov,

	selinux@tycho.nsa.gov, bfields@fieldses.org

Subject: [PATCH] fs: call security_d_instantiate in d_obtain_alias V2

Date:	Thu, 18 Nov 2010 20:52:55 -0500

Message-Id: <1290131575-2489-1-git-send-email-josef@redhat.com>

X-Mailing-List:	linux-fsdevel@vger.kernel.org

While trying to track down some NFS problems with BTRFS, I kept noticing I was

getting -EACCESS for no apparent reason.  Eric Paris and printk() helped me

figure out that it was SELinux that was giving me grief, with the following

denial

type=AVC msg=audit(1290013638.413:95): avc:  denied  { 0x800000 } for  pid=1772

comm="nfsd" name="" dev=sda1 ino=256 scontext=system_u:system_r:kernel_t:s0

tcontext=system_u:object_r:unlabeled_t:s0 tclass=file

Turns out this is because in d_obtain_alias if we can't find an alias we create

one and do all the normal instantiation stuff, but we don't do the

security_d_instantiate.

Usually we are protected from getting a hashed dentry that hasn't yet run

security_d_instantiate() by the parent's i_mutex, but obviously this isn't an

option there, so in order to deal with the case that a second thread comes in

and finds our new dentry before we get to run security_d_instantiate(), we go

ahead and call it if we find a dentry already.  Eric assures me that this is ok

as the code checks to see if the dentry has been initialized already so calling

security_d_instantiate() against the same dentry multiple times is ok.  With

this patch I'm no longer getting errant -EACCESS values.

Signed-off-by: Josef Bacik <josef@redhat.com>

---

V1->V2:

-added second security_d_instantiate() call

 fs/dcache.c |    3 +++

 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c

index 5699d4c..85388fc 100644

--- a/fs/dcache.c

+++ b/fs/dcache.c

@@ -1577,9 +1577,13 @@ struct dentry *d_obtain_alias(struct inode *inode)

 	spin_unlock(&tmp->d_lock);

 	spin_unlock(&inode->i_lock);

+	security_d_instantiate(tmp, inode);

+

 	return tmp;

  out_iput:

+	if (res && !IS_ERR(res))

+		security_d_instantiate(res, inode);

 	iput(inode);

 	return res;

 }

--

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