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@suse.de>
Fixes: 78599c42ae3c ("nfsd4: add file to display list of client's opens")
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index cce2510..c905631 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -507,6 +507,17 @@ find_any_file(struct nfs4_file *f)
        return ret;
 }
 
+static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
+{
+       struct nfsd_file *ret = NULL;
+
+       spin_lock(&f->fi_lock);
+       if (f->fi_deleg_file)
+               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 +2455,8 @@ 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 +2494,8 @@ 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 +2528,9 @@ 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 +2546,7 @@ 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;
 }