Re: nfs4_show_superblock considered harmful :-)

["J. Bruce Fields" <bfields@xxxxxxxxxxxx>]

On Wed, Jul 15, 2020 at 02:54:56PM -0400, J. Bruce Fields wrote:
> commit 4eef57aa4fc0
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date:   Wed Jul 15 13:31:36 2020 -0400
> 
>     nfsd4: fix NULL dereference in nfsd/clients display code
>     
>     Reported-by: NeilBrown <neilb@xxxxxxx>
>     Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index ab5c8857ae5a..08b8376c74d7 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -507,6 +507,16 @@ find_any_file(struct nfs4_file *f)
>  	return ret;
>  }
>  
> +static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
> +{
> +	struct nfsd_file *ret;
> +
> +	spin_lock(&f->fi_lock);
> +	ret = nfsd_file_get(f->fi_deleg_file);
> +	spin_unlock(&f->fi_lock);
> +	return ret;
> +}
> +
...
> @@ -2513,7 +2527,9 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)
>  
>  	ds = delegstateid(st);
>  	nf = st->sc_file;
> -	file = nf->fi_deleg_file;
> +	file = find_deleg_file(nf);
> +	if (!file)
> +		return 0;
>  
>  	seq_printf(s, "- ");
>  	nfs4_show_stateid(s, &st->sc_stateid);

Oops, I added a "get" without a corresponding "put".

--b.

commit 8d2edfe45286
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
Date:   Wed Jul 15 13:31:36 2020 -0400

    nfsd4: fix NULL dereference in nfsd/clients display code
    
    We hold the cl_lock here, and that's enough to keep stateid's from going
    away, but it's not enough to prevent the files they point to from going
    away.  Take fi_lock and a reference and check for NULL, as we do in
    other code.
    
    Reported-by: NeilBrown <neilb@xxxxxxx>
    Fixes: 78599c42ae3c ("nfsd4: add file to display list of client's opens")
    Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index ab5c8857ae5a..9d45117c8c18 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -507,6 +507,16 @@ find_any_file(struct nfs4_file *f)
 	return ret;
 }
 
+static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
+{
+	struct nfsd_file *ret;
+
+	spin_lock(&f->fi_lock);
+	ret = nfsd_file_get(f->fi_deleg_file);
+	spin_unlock(&f->fi_lock);
+	return ret;
+}
+
 static atomic_long_t num_delegations;
 unsigned long max_delegations;
 
@@ -2444,6 +2454,8 @@ static int nfs4_show_open(struct seq_file *s, struct nfs4_stid *st)
 	oo = ols->st_stateowner;
 	nf = st->sc_file;
 	file = find_any_file(nf);
+	if (!file)
+		return 0;
 
 	seq_printf(s, "- ");
 	nfs4_show_stateid(s, &st->sc_stateid);
@@ -2481,6 +2493,8 @@ static int nfs4_show_lock(struct seq_file *s, struct nfs4_stid *st)
 	oo = ols->st_stateowner;
 	nf = st->sc_file;
 	file = find_any_file(nf);
+	if (!file)
+		return 0;
 
 	seq_printf(s, "- ");
 	nfs4_show_stateid(s, &st->sc_stateid);
@@ -2513,7 +2527,9 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)
 
 	ds = delegstateid(st);
 	nf = st->sc_file;
-	file = nf->fi_deleg_file;
+	file = find_deleg_file(nf);
+	if (!file)
+		return 0;
 
 	seq_printf(s, "- ");
 	nfs4_show_stateid(s, &st->sc_stateid);
@@ -2529,6 +2545,7 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)
 	seq_printf(s, ", ");
 	nfs4_show_fname(s, file);
 	seq_printf(s, " }\n");
+	nfsd_file_put(file);
 
 	return 0;
 }