fanotify: update connector fsid cache on add mark

When implementing connector fsid cache, we only initialized the cache
when the first mark added to object was added by FAN_REPORT_FID group.
We forgot to update conn->fsid when the second mark is added by
FAN_REPORT_FID group to an already attached connector without fsid
cache.

Reported-and-tested-by: syzbot+c277e8e2f46414645508@syzkaller.appspotmail.com
Fixes: 77115225acc6 ("fanotify: cache fsid in fsnotify_mark_connector")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

3 files changed, 18 insertions, 4 deletions

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index e6fde1a5c072..b428c295d13f 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -355,6 +355,10 @@ static __kernel_fsid_t fanotify_get_fsid(struct fsnotify_iter_info *iter_info)
                 /* Mark is just getting destroyed or created? */
                 if (!conn)
                         continue;
+                if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID))
+                        continue;
+                /* Pairs with smp_wmb() in fsnotify_add_mark_list() */
+                smp_rmb();
                 fsid = conn->fsid;
                 if (WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1]))
                         continue;
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 25eb247ea85a..99ddd126f6f0 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -482,10 +482,13 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
         conn->type = type;
         conn->obj = connp;
         /* Cache fsid of filesystem containing the object */
-        if (fsid)
+        if (fsid) {
                 conn->fsid = *fsid;
-        else
+                conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID;
+        } else {
                 conn->fsid.val[0] = conn->fsid.val[1] = 0;
+                conn->flags = 0;
+        }
         if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
                 inode = igrab(fsnotify_conn_inode(conn));
         /*
@@ -560,7 +563,12 @@ restart:
                 if (err)
                         return err;
                 goto restart;
-        } else if (fsid && (conn->fsid.val[0] || conn->fsid.val[1]) &&
+        } else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) {
+                conn->fsid = *fsid;
+                /* Pairs with smp_rmb() in fanotify_get_fsid() */
+                smp_wmb();
+                conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID;
+        } else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) &&
                    (fsid->val[0] != conn->fsid.val[0] ||
                     fsid->val[1] != conn->fsid.val[1])) {
                 /*
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index a9f9dcc1e515..d4844cad2c2b 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -292,7 +292,9 @@ typedef struct fsnotify_mark_connector __rcu *fsnotify_connp_t;
  */
 struct fsnotify_mark_connector {
         spinlock_t lock;
-        unsigned int type;      /* Type of object [lock] */
+        unsigned short type;    /* Type of object [lock] */
+#define FSNOTIFY_CONN_FLAG_HAS_FSID     0x01
+        unsigned short flags;   /* flags [lock] */
         __kernel_fsid_t fsid;   /* fsid of filesystem containing object */
         union {
                 /* Object pointer [lock] */