[PATCH 14/25] virtiofsd: prevent ".." escape in lo_do_readdir()

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Stefan Hajnoczi <stefanha@redhat.com>

Construct a fake dirent for the root directory's ".." entry.  This hides
the parent directory from the FUSE client.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 contrib/virtiofsd/passthrough_ll.c | 36 ++++++++++++++++++------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
index 7a61bf94fe..cb01e3f088 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -1087,18 +1087,24 @@ out_err:
 static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
 			  off_t offset, struct fuse_file_info *fi, int plus)
 {
+	struct lo_data *lo = lo_data(req);
 	struct lo_dirp *d;
+	struct lo_inode *dinode;
 	char *buf = NULL;
 	char *p;
 	size_t rem = size;
-	int err = ENOMEM;
+	int err = EBADF;
 
-	(void) ino;
+	dinode = lo_inode(req, ino);
+	if (!dinode) {
+		goto error;
+	}
 
 	d = lo_dirp(req, fi);
 	if (!d)
 		goto error;
 
+	err = ENOMEM;
 	buf = calloc(1, size);
 	if (!buf)
 		goto error;
@@ -1128,15 +1134,21 @@ static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
 		}
 		nextoff = d->entry->d_off;
 		name = d->entry->d_name;
+
 		fuse_ino_t entry_ino = 0;
+		struct fuse_entry_param e = (struct fuse_entry_param) {
+			.attr.st_ino = d->entry->d_ino,
+			.attr.st_mode = d->entry->d_type << 12,
+		};
+
+		/* Hide root's parent directory */
+		if (dinode == &lo->root && strcmp(name, "..") == 0) {
+			e.attr.st_ino = lo->root.ino;
+			e.attr.st_mode = DT_DIR << 12;
+		}
+
 		if (plus) {
-			struct fuse_entry_param e;
-			if (is_dot_or_dotdot(name)) {
-				e = (struct fuse_entry_param) {
-					.attr.st_ino = d->entry->d_ino,
-					.attr.st_mode = d->entry->d_type << 12,
-				};
-			} else {
+			if (!is_dot_or_dotdot(name)) {
 				err = lo_do_lookup(req, ino, name, &e);
 				if (err)
 					goto error;
@@ -1146,12 +1158,8 @@ static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
 			entsize = fuse_add_direntry_plus(req, p, rem, name,
 							 &e, nextoff);
 		} else {
-			struct stat st = {
-				.st_ino = d->entry->d_ino,
-				.st_mode = d->entry->d_type << 12,
-			};
 			entsize = fuse_add_direntry(req, p, rem, name,
-						    &st, nextoff);
+						    &e.attr, nextoff);
 		}
 		if (entsize > rem) {
 			if (entry_ino != 0) 
-- 
2.23.0