On Wed, Nov 17, 2010 at 12:51:03PM -0500, Josef Bacik wrote:
> 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. With this patch I'm no longer seeing these errant
> -EACCESS return values. Thanks,
Possibly dumb question: Is there still a small race here? Is it
possible for another nfsd thread to find the new alias on the list while
this thread is still:
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
> ---
> fs/dcache.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 23702a9..890a59e 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1201,6 +1201,7 @@ struct dentry *d_obtain_alias(struct inode *inode)
> spin_unlock(&tmp->d_lock);
>
> spin_unlock(&dcache_lock);
... right here, so that that other nfsd thread still ends up trying to
do something with a dentry that hasn't had security_d_instantiate called
on it yet?
> + security_d_instantiate(tmp, inode);
> return tmp;
>
> out_iput:
> --
Or does something else prevent that?
--b.
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