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.

[drosen: I've combined this patch with a few others that fix dealing
with error codes (mostly ENOSYS) to make it harder to lose these again
in the future:

ANDROID: fsnotify: Do not notify lower fs of open when ENOSYS
ANDROID: fuse: Skip canonical path logic if ENOSYS
ANDROID: fuse: Fix the issue of fuse_dentry_canonical_path ]

Bug: 238619640
Test: inotify no longer works on /storage/emulated/0/Android/media but
      does on child folders
Bug: 326995824
Test: cts-tradefed run commandAndExit cts -m CtsOsTestCases -t android.os.cts.FileObserverTest
Bug: 330136711
Test: ./cts-tradefed run commandAndExit cts -m CtsIncidentHostTestCases -t com.android.server.cts.ErrorsTest#testTombstone

Signed-off-by: Paul Lawrence <paullawrence@google.com>
Change-Id: Icb15c090c6286c174338471a787712f8388de316

fs/fuse/dev.c

@@ -2041,7 +2041,7 @@ 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

@@ -333,7 +333,7 @@ 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);
@@ -343,9 +343,12 @@ static void fuse_dentry_canonical_path(const struct path *path,
 	char *path_name;
 	int err;
 
+	if (fm->fc->no_dentry_canonical_path)
+		goto out;
+
 	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);
@@ -359,11 +362,18 @@ 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 && err != -ENOSYS)
+		return err;
+
+	if (err == -ENOSYS)
+		fm->fc->no_dentry_canonical_path = 1;
+
+out:
 	canonical_path->dentry = path->dentry;
 	canonical_path->mnt = path->mnt;
 	path_get(canonical_path);
+	return 0;
 }
 
 const struct dentry_operations fuse_dentry_operations = {

fs/fuse/fuse_i.h

@@ -773,6 +773,9 @@ struct fuse_conn {
 	/** Is bmap not implemented by fs? */
 	unsigned no_bmap:1;
 
+	/** Is dentry_canonical_path not implemented by fs? */
+	unsigned no_dentry_canonical_path:1;
+
 	/** Is poll not implemented by fs? */
 	unsigned no_poll:1;
 

fs/notify/inotify/inotify_user.c

@@ -783,10 +783,15 @@ 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);
-			canonical_path = &alteredpath;
-			path_put(&path);
+			if (ret != -ENOSYS) {
+				if (ret) {
+					goto path_put_and_out;
+				}
+				canonical_path = &alteredpath;
+				path_put(&path);
+			}
 		}
 	}
 
@@ -796,6 +801,7 @@ 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

@@ -150,7 +150,7 @@ struct dentry_operations {
 	struct vfsmount *(*d_automount)(struct path *);
 	int (*d_manage)(const struct path *, bool);
 	struct dentry *(*d_real)(struct dentry *, enum d_real_type type);
-	void (*d_canonical_path)(const struct path *, struct path *);
+	int (*d_canonical_path)(const struct path *, struct path *);
 } ____cacheline_aligned;
 
 /*

include/linux/fsnotify.h

@@ -137,13 +137,19 @@ 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 = fsnotify_parent(lower_path.dentry, mask,
-					      &lower_path, FSNOTIFY_EVENT_PATH);
-			path_put(&lower_path);
+			ret = path->dentry->d_op->d_canonical_path(path,
+								   &lower_path);
+			if (ret != -ENOSYS) {
+				if (ret)
+					return ret;
 
-			if (ret)
-				return ret;
+				ret = fsnotify_parent(lower_path.dentry, mask,
+						      &lower_path, FSNOTIFY_EVENT_PATH);
+				path_put(&lower_path);
+
+				if (ret)
+					return ret;
+			}
 		}
 	}