Re: [PATCH] nfs: Fix potential posix_acl refcnt leak in nfs3_set_acl

[Trond Myklebust <trondmy@hammerspace.com>]

On Mon, 2020-04-20 at 13:43 +0800, Xiyu Yang wrote:
> nfs3_set_acl() invokes get_acl(), which returns a local reference of
> the
> posix_acl object to "alloc" with increased refcount.
> 
> When nfs3_set_acl() returns or a new object is assigned to
> "alloc",  the
> original local reference of  "alloc" becomes invalid, so the refcount
> should be decreased to keep refcount balanced.
> 
> The reference counting issue happens in one path of nfs3_set_acl().
> When
> "acl" equals to NULL but "alloc" is not NULL, the function forgets to
> decrease the refcnt increased by get_acl() and causes a refcnt leak.
> 
> Fix this issue by calling posix_acl_release() on this path when
> "alloc"
> is not NULL.
> 
> Fixes: b7fa0554cf1b ("[PATCH] NFS: Add support for NFSv3 ACLs")
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  fs/nfs/nfs3acl.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/nfs/nfs3acl.c b/fs/nfs/nfs3acl.c
> index c5c3fc6e6c60..b5c41bcca8cf 100644
> --- a/fs/nfs/nfs3acl.c
> +++ b/fs/nfs/nfs3acl.c
> @@ -274,6 +274,8 @@ int nfs3_set_acl(struct inode *inode, struct
> posix_acl *acl, int type)
>  	}
>  
>  	if (acl == NULL) {
> +		if (alloc)
> +			posix_acl_release(alloc);

This will result in 'dfacl' being freed while it is still in use, so
can't be correct either.

>  		alloc = acl = posix_acl_from_mode(inode->i_mode,
> GFP_KERNEL);
>  		if (IS_ERR(alloc))
>  			goto fail;

I don't really see any alternative to adding a 'dfalloc' to track the
allocated dfacl separately.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com