[34-longterm 230/247] fs: call security_d_instantiate in d_obtain_alias V2

Paul Gortmaker
2011-06-23T17:46:06Z

From: Josef Bacik <josef@redhat.com>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------

commit 24ff6663ccfdaf088dfa7acae489cb11ed4f43c4 upstream

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>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
fs/dcache.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 2b6f09a..68c70f0 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1187,9 +1187,12 @@ 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;
}
--
1.7.4.4