On Thu, 2010-11-18 at 20:52 -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.
>
> 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>
Acked-by: Eric Paris <eparis@xxxxxxxxxx>
Al, any chance we can push this along?
-Eric
> ---
> 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;
> }
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