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Date:      Fri, 27 Sep 2019 16:22:28 +0000 (UTC)
From:      Andrew Turner <andrew@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r352796 - head/sys/kern
Message-ID:  <201909271622.x8RGMS3v043138@repo.freebsd.org>
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Author: andrew
Date: Fri Sep 27 16:22:28 2019
New Revision: 352796
URL: https://svnweb.freebsd.org/changeset/base/352796

Log:
  Check the vfs option length is valid before accessing through
  
  When a VFS option passed to nmount is present but NULL the kernel will
  place an empty option in its internal list. This will have a NULL
  pointer and a length of 0. When we come to read one of these the kernel
  will try to load from the last address of virtual memory. This is
  normally invalid so will fault resulting in a kernel panic.
  
  Fix this by checking if the length is valid before dereferencing.
  
  MFC after:	3 days
  Sponsored by:	DARPA, AFRL

Modified:
  head/sys/kern/vfs_mount.c

Modified: head/sys/kern/vfs_mount.c
==============================================================================
--- head/sys/kern/vfs_mount.c	Fri Sep 27 16:11:47 2019	(r352795)
+++ head/sys/kern/vfs_mount.c	Fri Sep 27 16:22:28 2019	(r352796)
@@ -646,7 +646,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, stru
 	 */
 	fstypelen = 0;
 	error = vfs_getopt(optlist, "fstype", (void **)&fstype, &fstypelen);
-	if (error || fstype[fstypelen - 1] != '\0') {
+	if (error || fstypelen <= 0 || fstype[fstypelen - 1] != '\0') {
 		error = EINVAL;
 		if (errmsg != NULL)
 			strncpy(errmsg, "Invalid fstype", errmsg_len);
@@ -654,7 +654,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, stru
 	}
 	fspathlen = 0;
 	error = vfs_getopt(optlist, "fspath", (void **)&fspath, &fspathlen);
-	if (error || fspath[fspathlen - 1] != '\0') {
+	if (error || fspathlen <= 0 || fspath[fspathlen - 1] != '\0') {
 		error = EINVAL;
 		if (errmsg != NULL)
 			strncpy(errmsg, "Invalid fspath", errmsg_len);

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