[PATCH] [241/275] fs: call security_d_instantiate in d_obtain_alias V2

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Josef Bacik <josef@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/dcache.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6.35.y/fs/dcache.c
===================================================================
--- linux-2.6.35.y.orig/fs/dcache.c	2011-03-29 22:50:16.864826890 -0700
+++ linux-2.6.35.y/fs/dcache.c	2011-03-29 23:03:03.231217492 -0700
@@ -1186,9 +1186,12 @@
 	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;
 }
--
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