[PATCH 5/6] afs: Provide an RCU-capable key lookup

From: David Howells
Date: Wed May 22 2019 - 18:49:26 EST


Provide an RCU-capable key lookup function. We don't want to call
afs_request_key() in RCU-mode pathwalk as request_key() might sleep, even if
we don't ask it to construct anything as it might find a key that is currently
undergoing construction.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

fs/afs/internal.h | 1 +
fs/afs/security.c | 27 +++++++++++++++++++++++++++
2 files changed, 28 insertions(+)

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 2073c1a3ab4b..3090efcc823f 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -1237,6 +1237,7 @@ extern void afs_cache_permit(struct afs_vnode *, struct key *, unsigned int,
struct afs_status_cb *);
extern void afs_zap_permits(struct rcu_head *);
extern struct key *afs_request_key(struct afs_cell *);
+extern struct key *afs_request_key_rcu(struct afs_cell *);
extern int afs_check_permit(struct afs_vnode *, struct key *, afs_access_t *);
extern int afs_permission(struct inode *, int);
extern void __exit afs_clean_up_permit_cache(void);
diff --git a/fs/afs/security.c b/fs/afs/security.c
index 5d8ece98561e..a6582d6a3882 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -49,6 +49,33 @@ struct key *afs_request_key(struct afs_cell *cell)
}
}

+/*
+ * Get a key when pathwalk is in rcuwalk mode.
+ */
+struct key *afs_request_key_rcu(struct afs_cell *cell)
+{
+ struct key *key;
+
+ _enter("{%x}", key_serial(cell->anonymous_key));
+
+ _debug("key %s", cell->anonymous_key->description);
+ key = request_key_rcu(&key_type_rxrpc, cell->anonymous_key->description);
+ if (IS_ERR(key)) {
+ if (PTR_ERR(key) != -ENOKEY) {
+ _leave(" = %ld", PTR_ERR(key));
+ return key;
+ }
+
+ /* act as anonymous user */
+ _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
+ return cell->anonymous_key;
+ } else {
+ /* act as authorised user */
+ _leave(" = {%x} [auth]", key_serial(key));
+ return key;
+ }
+}
+
/*
* Dispose of a list of permits.
*/