[PATCH v3] seccomp: Add find_notification helper

[Sargun Dhillon]

This adds a helper which can iterate through a seccomp_filter to
find a notification matching an ID. It removes several replicated
chunks of code.

Signed-off-by: Sargun Dhillon <sar...@sargun.me>
Acked-by: Christian Brauner <christian.brau...@ubuntu.com>
Reviewed-by: Tycho Andersen <ty...@tycho.ws>
Cc: Matt Denton <mpden...@google.com>
Cc: Kees Cook <keesc...@google.com>,
Cc: Jann Horn <ja...@google.com>,
Cc: Robert Sesek <rse...@google.com>,
Cc: Chris Palmer <pal...@google.com>
Cc: Christian Brauner <christian.brau...@ubuntu.com>
Cc: Tycho Andersen <ty...@tycho.ws>
---
 kernel/seccomp.c | 55 ++++++++++++++++++++++++------------------------
 1 file changed, 28 insertions(+), 27 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 55a6184f5990..cc6b47173a95 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -41,6 +41,7 @@
 #include <linux/tracehook.h>
 #include <linux/uaccess.h>
 #include <linux/anon_inodes.h>
+#include <linux/lockdep.h>
 
 enum notify_state {
        SECCOMP_NOTIFY_INIT,
@@ -1021,10 +1022,27 @@ static int seccomp_notify_release(struct inode *inode, 
struct file *file)
        return 0;
 }
 
+/* must be called with notif_lock held */
+static inline struct seccomp_knotif *
+find_notification(struct seccomp_filter *filter, u64 id)
+{
+       struct seccomp_knotif *cur;
+
+       lockdep_assert_held(&filter->notify_lock);
+
+       list_for_each_entry(cur, &filter->notif->notifications, list) {
+               if (cur->id == id)
+                       return cur;
+       }
+
+       return NULL;
+}
+
+
 static long seccomp_notify_recv(struct seccomp_filter *filter,
                                void __user *buf)
 {
-       struct seccomp_knotif *knotif = NULL, *cur;
+       struct seccomp_knotif *knotif, *cur;
        struct seccomp_notif unotif;
        ssize_t ret;
 
@@ -1078,15 +1096,8 @@ static long seccomp_notify_recv(struct seccomp_filter 
*filter,
                 * may have died when we released the lock, so we need to make
                 * sure it's still around.
                 */
-               knotif = NULL;
                mutex_lock(&filter->notify_lock);
-               list_for_each_entry(cur, &filter->notif->notifications, list) {
-                       if (cur->id == unotif.id) {
-                               knotif = cur;
-                               break;
-                       }
-               }
-
+               knotif = find_notification(filter, unotif.id);
                if (knotif) {
                        knotif->state = SECCOMP_NOTIFY_INIT;
                        up(&filter->notif->request);
@@ -1101,7 +1112,7 @@ static long seccomp_notify_send(struct seccomp_filter 
*filter,
                                void __user *buf)
 {
        struct seccomp_notif_resp resp = {};
-       struct seccomp_knotif *knotif = NULL, *cur;
+       struct seccomp_knotif *knotif;
        long ret;
 
        if (copy_from_user(&resp, buf, sizeof(resp)))
@@ -1118,13 +1129,7 @@ static long seccomp_notify_send(struct seccomp_filter 
*filter,
        if (ret < 0)
                return ret;
 
-       list_for_each_entry(cur, &filter->notif->notifications, list) {
-               if (cur->id == resp.id) {
-                       knotif = cur;
-                       break;
-               }
-       }
-
+       knotif = find_notification(filter, resp.id);
        if (!knotif) {
                ret = -ENOENT;
                goto out;
@@ -1150,7 +1155,7 @@ static long seccomp_notify_send(struct seccomp_filter 
*filter,
 static long seccomp_notify_id_valid(struct seccomp_filter *filter,
                                    void __user *buf)
 {
-       struct seccomp_knotif *knotif = NULL;
+       struct seccomp_knotif *knotif;
        u64 id;
        long ret;
 
@@ -1161,16 +1166,12 @@ static long seccomp_notify_id_valid(struct 
seccomp_filter *filter,
        if (ret < 0)
                return ret;
 
-       ret = -ENOENT;
-       list_for_each_entry(knotif, &filter->notif->notifications, list) {
-               if (knotif->id == id) {
-                       if (knotif->state == SECCOMP_NOTIFY_SENT)
-                               ret = 0;
-                       goto out;
-               }
-       }
+       knotif = find_notification(filter, id);
+       if (knotif && knotif->state == SECCOMP_NOTIFY_SENT)
+               ret = 0;
+       else
+               ret = -ENOENT;
 
-out:
        mutex_unlock(&filter->notify_lock);
        return ret;
 }
-- 
2.25.1