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From: Conrad Meyer <cem@FreeBSD.org>
Date: Fri, 29 Sep 2017 15:53:26 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r324102 - head/sys/netsmb
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Author: cem
Date: Fri Sep 29 15:53:26 2017
New Revision: 324102
URL: https://svnweb.freebsd.org/changeset/base/324102

Log:
  netsmb: Fix buggy/racy smb_strdupin()
  
  smb_strdupin() tried to roll a copyin() based strlen to allocate a buffer
  and then blindly copyin that size.  Of course, a malicious user program
  could simultaneously manipulate the buffer, resulting in a non-terminated
  string being copied.
  
  Later assumptions in the code rely upon the string being nul-terminated.
  
  Just use copyinstr() and drop the racy sizing.
  
  PR:		222687
  Reported by:	Meng Xu <meng.xu AT gatech.edu>
  Security:	possible local DoS
  Sponsored by:	Dell EMC Isilon

Modified:
  head/sys/netsmb/smb_subr.c

Modified: head/sys/netsmb/smb_subr.c
==============================================================================
--- head/sys/netsmb/smb_subr.c	Fri Sep 29 15:13:28 2017	(r324101)
+++ head/sys/netsmb/smb_subr.c	Fri Sep 29 15:53:26 2017	(r324102)
@@ -110,22 +110,11 @@ smb_strdup(const char *s)
 char *
 smb_strdupin(char *s, size_t maxlen)
 {
-	char *p, bt;
+	char *p;
 	int error;
-	size_t len;
 
-	len = 0;
-	for (p = s; ;p++) {
-		if (copyin(p, &bt, 1))
-			return NULL;
-		len++;
-		if (maxlen && len > maxlen)
-			return NULL;
-		if (bt == 0)
-			break;
-	}
-	p = malloc(len, M_SMBSTR, M_WAITOK);
-	error = copyin(s, p, len);
+	p = malloc(maxlen + 1, M_SMBSTR, M_WAITOK);
+	error = copyinstr(s, p, maxlen + 1, NULL);
 	if (error) {
 		free(p, M_SMBSTR);
 		return (NULL);