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 23702a9..119d489 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1201,9 +1201,12 @@ struct dentry *d_obtain_alias(struct inode *inode)
spin_unlock(&tmp->d_lock);
spin_unlock(&dcache_lock);
+ security_d_instantiate(tmp, inode);
return tmp;
out_iput:
+ if (res && !IS_ERR(res))
+ security_d_instantiate(res, inode);
iput(inode);
return res;
}
--
1.6.6.1
--
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