svcrpc: fix double-free on shutdown of nfsd after changing pool mode

The pool_to and to_pool fields of the global svc_pool_map are freed on shutdown, but are initialized in nfsd startup only in the SVC_POOL_PERCPU and SVC_POOL_PERNODE cases. They *are* initialized to zero on kernel startup. So as long as you use only SVC_POOL_GLOBAL (the default), this will never be a problem. You're also OK if you only ever use SVC_POOL_PERCPU or SVC_POOL_PERNODE. However, the following sequence events leads to a double-free: 1. set SVC_POOL_PERCPU or SVC_POOL_PERNODE 2. start nfsd: both fields are initialized. 3. shutdown nfsd: both fields are freed. 4. set SVC_POOL_GLOBAL 5. start nfsd: the fields are left untouched. 6. shutdown nfsd: now we try to free them again. Step 4 is actually unnecessary, since (for some bizarre reason), nfsd automatically resets the pool mode to SVC_POOL_GLOBAL on shutdown. Cc: stable@kernel.org Signed-off-by: J. Bruce Fields <bfields@redhat.com>
nomis · Jan 5, 2012 · 61c8504 · 61c8504
1 parent b854889
commit 61c8504
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
@@ -167,6 +167,7 @@ svc_pool_map_alloc_arrays(struct svc_pool_map *m, unsigned int maxpools)
 
 fail_free:
 	kfree(m->to_pool);
+	m->to_pool = NULL;
 fail:
 	return -ENOMEM;
 }
@@ -287,7 +288,9 @@ svc_pool_map_put(void)
 	if (!--m->count) {
 		m->mode = SVC_POOL_DEFAULT;
 		kfree(m->to_pool);
+		m->to_pool = NULL;
 		kfree(m->pool_to);
+		m->pool_to = NULL;
 		m->npools = 0;
 	}