ANDROID: fuse: Support errors from fuse daemon in canonical path

Previously errors from the daemon in FUSE_CANONICAL_PATH were simply
ignored. In order to block inotifys, it is useful to be able to return
errors from this opcode.

Bug: 238619640
Test: inotify no longer works on /storage/emulated/0/Android/media but
      does on child folders
Change-Id: I1c65814f4ad0ccef330bca9764c2db15c71bf2be
Signed-off-by: Paul Lawrence <paullawrence@google.com>

fs/fuse/dev.c

@@ -1941,7 +1941,7 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
 		err = copy_out_args(cs, req->args, nbytes);
 	fuse_copy_finish(cs);
 
-	if (!err && req->in.h.opcode == FUSE_CANONICAL_PATH) {
+	if (!err && req->in.h.opcode == FUSE_CANONICAL_PATH && !oh.error) {
 		char *path = (char *)req->args->out_args[0].value;
 
 		path[req->args->out_args[0].size - 1] = 0;

fs/fuse/dir.c

@@ -395,7 +395,7 @@ static struct vfsmount *fuse_dentry_automount(struct path *path)
  * look up paths on its own. Instead, we handle the lookup as a special case
  * inside of the write request.
  */
-static void fuse_dentry_canonical_path(const struct path *path,
+static int fuse_dentry_canonical_path(const struct path *path,
 				       struct path *canonical_path)
 {
 	struct inode *inode = d_inode(path->dentry);
@@ -414,12 +414,12 @@ static void fuse_dentry_canonical_path(const struct path *path,
 			       fuse_canonical_path_finalize, path,
 			       canonical_path);
 	if (fer.ret)
-		return;
+		return PTR_ERR(fer.result);
 #endif
 
 	path_name = (char *)get_zeroed_page(GFP_KERNEL);
 	if (!path_name)
-		goto default_path;
+		return -ENOMEM;
 
 	args.opcode = FUSE_CANONICAL_PATH;
 	args.nodeid = get_node_id(inode);
@@ -433,11 +433,14 @@ static void fuse_dentry_canonical_path(const struct path *path,
 	err = fuse_simple_request(fm, &args);
 	free_page((unsigned long)path_name);
 	if (err > 0)
-		return;
-default_path:
+		return 0;
+	if (err < 0)
+		return err;
+
 	canonical_path->dentry = path->dentry;
 	canonical_path->mnt = path->mnt;
 	path_get(canonical_path);
+	return 0;
 }
 
 const struct dentry_operations fuse_dentry_operations = {

fs/notify/inotify/inotify_user.c

@@ -763,8 +763,11 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
 	/* support stacked filesystems */
 	if (path.dentry && path.dentry->d_op) {
 		if (path.dentry->d_op->d_canonical_path) {
-			path.dentry->d_op->d_canonical_path(&path,
+			ret = path.dentry->d_op->d_canonical_path(&path,
 							    &alteredpath);
+			if (ret)
+				goto path_put_and_out;
+
 			canonical_path = &alteredpath;
 			path_put(&path);
 		}
@@ -776,6 +779,7 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
 
 	/* create/update an inode mark */
 	ret = inotify_update_watch(group, inode, mask);
+path_put_and_out:
 	path_put(canonical_path);
 fput_and_out:
 	fdput(f);

include/linux/dcache.h

@@ -153,7 +153,7 @@ struct dentry_operations {
 	struct vfsmount *(*d_automount)(struct path *);
 	int (*d_manage)(const struct path *, bool);
 	struct dentry *(*d_real)(struct dentry *, const struct inode *);
-	void (*d_canonical_path)(const struct path *, struct path *);
+	int (*d_canonical_path)(const struct path *, struct path *);
 	ANDROID_KABI_RESERVE(1);
 	ANDROID_KABI_RESERVE(2);
 	ANDROID_KABI_RESERVE(3);

include/linux/fsnotify.h

@@ -105,7 +105,11 @@ static inline int fsnotify_file(struct file *file, __u32 mask)
 			struct path lower_path;
 			int ret;
 
-			path->dentry->d_op->d_canonical_path(path, &lower_path);
+			ret = path->dentry->d_op->d_canonical_path(path,
+								   &lower_path);
+			if (ret)
+				return ret;
+
 			ret = fsnotify_parent(lower_path.dentry, mask,
 					      &lower_path, FSNOTIFY_EVENT_PATH);
 			path_put(&lower_path);