Do a basic sanity check that dirents returned via fuse are kind of sane.

Ensure that file names passed back by readdir do not include a '/'
character. The '/' char is the path separator and is not allowed in
any filename. On top of this also check that d_reclen and d_namlen
are kind of sane and zero out the padding bytes after d_name.

OK beck@

1 files changed, 32 insertions, 1 deletions

diff --git a/sys/miscfs/fuse/fuse_vnops.c b/sys/miscfs/fuse/fuse_vnops.c
index 8c38ab55c41..c1592e7f5e7 100644
--- a/sys/miscfs/fuse/fuse_vnops.c
+++ b/sys/miscfs/fuse/fuse_vnops.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: fuse_vnops.c,v 1.69 2024/05/13 11:17:40 semarie Exp $ */
+/* $OpenBSD: fuse_vnops.c,v 1.70 2024/09/12 09:10:46 claudio Exp $ */
 /*
  * Copyright (c) 2012-2013 Sylvestre Gallon <ccna.syl@gmail.com>
  *
@@ -752,6 +752,8 @@ fusefs_readdir(void *v)
 	struct fusefs_node *ip;
 	struct fusefs_mnt *fmp;
 	struct fusebuf *fbuf;
+	struct dirent *dp;
+	char *edp;
 	struct vnode *vp;
 	struct proc *p;
 	struct uio *uio;
@@ -806,6 +808,35 @@ fusefs_readdir(void *v)
 			break;
 		}
 
+		/* validate the returned dirents */
+		dp = (struct dirent *)fbuf->fb_dat;
+		edp = fbuf->fb_dat + fbuf->fb_len;
+		while ((char *)dp < edp) {
+			if ((char *)dp + offsetof(struct dirent, d_name) >= edp
+			    || dp->d_reclen <= offsetof(struct dirent, d_name)
+			    || (char *)dp + dp->d_reclen > edp) {
+				error = EINVAL;
+				break;
+			}
+			if (dp->d_namlen + offsetof(struct dirent, d_name) >=
+			    dp->d_reclen) {
+				error = EINVAL;
+				break;
+			}
+			memset(dp->d_name + dp->d_namlen, 0, dp->d_reclen -
+			    dp->d_namlen - offsetof(struct dirent, d_name));
+
+			if (memchr(dp->d_name, '/', dp->d_namlen) != NULL) {
+				error = EINVAL;
+				break;
+			}
+			dp = (struct dirent *)((char *)dp + dp->d_reclen);
+		}
+		if (error) {
+			fb_delete(fbuf);
+			break;
+		}
+
 		if ((error = uiomove(fbuf->fb_dat, fbuf->fb_len, uio))) {
 			fb_delete(fbuf);
 			break;