CVE-2018-18311: Out-of-bounds Write (CWE-787)
value: Perl before 5.26.3 and 5.28.x before 5.28.1 has a buffer overflow via a crafted regular expression that triggers invalid write operations.
CWE description: The product writes data past the end, or before the beginning, of the intended buffer.
CVSS v3 base score: 9.8
Published: 2018-12-07T21:29Z
Repository: https://github.com/Perl/perl5
Language: C
Files changed: util.c
Commit date: 2018-06-29 14:03:57 +0100
Commit message: Perl_my_setenv(); handle integer wrap

RT #133204

Wean this function off int/I32 and onto UV/Size_t.
Also, replace all malloc-ish calls with a wrapper that does
overflow checks,

In particular, it was doing (nlen + vlen + 2) which could wrap when
the combined length of the environment variable name and value
exceeded around 0x7fffffff.

The wrapper check function is probably overkill, but belt and braces...

NB this function has several variant parts, #ifdef'ed by platform
type; I have blindly changed the parts that aren't compiled under linux.

Diff: diff --git a/util.c b/util.c
index 7282dd9cfe..c5c7becc0f 100644
--- a/util.c
+++ b/util.c
@@ -2059,12 +2059,44 @@ Perl_new_warnings_bitfield(pTHX_ STRLEN *buffer, const char *const bits,
    *(s+nlen) = '='; \
    Copy(val, s+(nlen+1), vlen, char); \
    *(s+(nlen+1+vlen)) = '\0'
 
 #ifdef USE_ENVIRON_ARRAY
-       /* VMS' my_setenv() is in vms.c */
+
+/* small wrapper for use by Perl_my_setenv that mallocs, or reallocs if
+ * 'current' is non-null, with up to three sizes that are added together.
+ * It handles integer overflow.
+ */
+static char *
+S_env_alloc(void *current, Size_t l1, Size_t l2, Size_t l3, Size_t size)
+{
+    void *p;
+    Size_t sl, l = l1 + l2;
+
+    if (l < l2)
+        goto panic;
+    l += l3;
+    if (l < l3)
+        goto panic;
+    sl = l * size;
+    if (sl < l)
+        goto panic;
+
+    p = current
+            ? safesysrealloc(current, sl)
+            : safesysmalloc(sl);
+    if (p)
+        return (char*)p;
+
+  panic:
+    croak_memory_wrap();
+}
+
+
+/* VMS' my_setenv() is in vms.c */
 #if !defined(WIN32) && !defined(NETWARE)
+
 void
 Perl_my_setenv(pTHX_ const char *nam, const char *val)
 {
   dVAR;
 #ifdef __amigaos4__
@@ -2076,32 +2108,31 @@ Perl_my_setenv(pTHX_ const char *nam, const char *val)
 #endif
   {
 #ifndef PERL_USE_SAFE_PUTENV
     if (!PL_use_safe_putenv) {
         /* most putenv()s leak, so we manipulate environ directly */
-        I32 i;
-        const I32 len = strlen(nam);
-        int nlen, vlen;
+        UV i;
+        Size_t vlen, nlen = strlen(nam);
 
         /* where does it go? */
         for (i = 0; environ[i]; i++) {
-            if (strnEQ(environ[i],nam,len) && environ[i][len] == '=')
+            if (strnEQ(environ[i], nam, nlen) && environ[i][nlen] == '=')
                 break;
         }
 
         if (environ == PL_origenviron) {   /* need we copy environment? */
-            I32 j;
-            I32 max;
+            UV j, max;
             char **tmpenv;
 
             max = i;
             while (environ[max])
                 max++;
-            tmpenv = (char**)safesysmalloc((max+2) * sizeof(char*));
+            /* XXX shouldn't that be max+1 rather than max+2 ??? - DAPM */
+            tmpenv = (char**)S_env_alloc(NULL, max, 2, 0, sizeof(char*));
             for (j=0; j<max; j++) {         /* copy environment */
-                const int len = strlen(environ[j]);
-                tmpenv[j] = (char*)safesysmalloc((len+1)*sizeof(char));
+                const Size_t len = strlen(environ[j]);
+                tmpenv[j] = S_env_alloc(NULL, len, 1, 0, 1);
                 Copy(environ[j], tmpenv[j], len+1, char);
             }
             tmpenv[max] = NULL;
             environ = tmpenv;               /* tell exec where it is now */
         }
@@ -2116,19 +2147,19 @@ Perl_my_setenv(pTHX_ const char *nam, const char *val)
 #else
             return;
 #endif
         }
         if (!environ[i]) {                 /* does not exist yet */
-            environ = (char**)safesysrealloc(environ, (i+2) * sizeof(char*));
+            environ = (char**)S_env_alloc(environ, i, 2, 0, sizeof(char*));
             environ[i+1] = NULL;    /* make sure it's null terminated */
         }
         else
             safesysfree(environ[i]);
-        nlen = strlen(nam);
+
         vlen = strlen(val);
 
-        environ[i] = (char*)safesysmalloc((nlen+vlen+2) * sizeof(char));
+        environ[i] = S_env_alloc(NULL, nlen, vlen, 2, 1);
         /* all that work just for this */
         my_setenv_format(environ[i], nam, nlen, val, vlen);
     } else {
 # endif
     /* This next branch should only be called #if defined(HAS_SETENV), but
@@ -2148,26 +2179,25 @@ Perl_my_setenv(pTHX_ const char *nam, const char *val)
 #   elif defined(HAS_UNSETENV)
         if (val == NULL) {
             if (environ) /* old glibc can crash with null environ */
                 (void)unsetenv(nam);
         } else {
-	    const int nlen = strlen(nam);
-	    const int vlen = strlen(val);
-	    char * const new_env =
-                (char*)safesysmalloc((nlen + vlen + 2) * sizeof(char));
+	    const Size_t nlen = strlen(nam);
+	    const Size_t vlen = strlen(val);
+	    char * const new_env = S_env_alloc(NULL, nlen, vlen, 2, 1);
             my_setenv_format(new_env, nam, nlen, val, vlen);
             (void)putenv(new_env);
         }
 #   else /* ! HAS_UNSETENV */
         char *new_env;
-	const int nlen = strlen(nam);
-	int vlen;
+	const Size_t nlen = strlen(nam);
+	Size_t vlen;
         if (!val) {
 	   val = "";
         }
         vlen = strlen(val);
-        new_env = (char*)safesysmalloc((nlen + vlen + 2) * sizeof(char));
+        new_env = S_env_alloc(NULL, nlen, vlen, 2, 1);
         /* all that work just for this */
         my_setenv_format(new_env, nam, nlen, val, vlen);
         (void)putenv(new_env);
 #   endif /* __CYGWIN__ */
 #ifndef PERL_USE_SAFE_PUTENV
@@ -2185,18 +2215,18 @@ my_setenv_out:
 void
 Perl_my_setenv(pTHX_ const char *nam, const char *val)
 {
     dVAR;
     char *envstr;
-    const int nlen = strlen(nam);
-    int vlen;
+    const Size_t nlen = strlen(nam);
+    Size_t vlen;
 
     if (!val) {
        val = "";
     }
     vlen = strlen(val);
-    Newx(envstr, nlen+vlen+2, char);
+    envstr = S_env_alloc(NULL, nlen, vlen, 2, 1);
     my_setenv_format(envstr, nam, nlen, val, vlen);
     (void)PerlEnv_putenv(envstr);
     Safefree(envstr);
 }
 

Vulnerable code:        /* VMS' my_setenv() is in vms.c */
        I32 i;
        const I32 len = strlen(nam);
        int nlen, vlen;
            if (strnEQ(environ[i],nam,len) && environ[i][len] == '=')
            I32 j;
            I32 max;
            tmpenv = (char**)safesysmalloc((max+2) * sizeof(char*));
                const int len = strlen(environ[j]);
                tmpenv[j] = (char*)safesysmalloc((len+1)*sizeof(char));
            environ = (char**)safesysrealloc(environ, (i+2) * sizeof(char*));
        nlen = strlen(nam);
        environ[i] = (char*)safesysmalloc((nlen+vlen+2) * sizeof(char));
	    const int nlen = strlen(nam);
	    const int vlen = strlen(val);
	    char * const new_env =
                (char*)safesysmalloc((nlen + vlen + 2) * sizeof(char));
	const int nlen = strlen(nam);
	int vlen;
        new_env = (char*)safesysmalloc((nlen + vlen + 2) * sizeof(char));
    const int nlen = strlen(nam);
    int vlen;
    Newx(envstr, nlen+vlen+2, char);
Fixed code: 
/* small wrapper for use by Perl_my_setenv that mallocs, or reallocs if
 * 'current' is non-null, with up to three sizes that are added together.
 * It handles integer overflow.
 */
static char *
S_env_alloc(void *current, Size_t l1, Size_t l2, Size_t l3, Size_t size)
{
    void *p;
    Size_t sl, l = l1 + l2;

    if (l < l2)
        goto panic;
    l += l3;
    if (l < l3)
        goto panic;
    sl = l * size;
    if (sl < l)
        goto panic;

    p = current
            ? safesysrealloc(current, sl)
            : safesysmalloc(sl);
    if (p)
        return (char*)p;

  panic:
    croak_memory_wrap();
}


/* VMS' my_setenv() is in vms.c */

        UV i;
        Size_t vlen, nlen = strlen(nam);
            if (strnEQ(environ[i], nam, nlen) && environ[i][nlen] == '=')
            UV j, max;
            /* XXX shouldn't that be max+1 rather than max+2 ??? - DAPM */
            tmpenv = (char**)S_env_alloc(NULL, max, 2, 0, sizeof(char*));
                const Size_t len = strlen(environ[j]);
                tmpenv[j] = S_env_alloc(NULL, len, 1, 0, 1);
            environ = (char**)S_env_alloc(environ, i, 2, 0, sizeof(char*));

        environ[i] = S_env_alloc(NULL, nlen, vlen, 2, 1);
	    const Size_t nlen = strlen(nam);
	    const Size_t vlen = strlen(val);
	    char * const new_env = S_env_alloc(NULL, nlen, vlen, 2, 1);
	const Size_t nlen = strlen(nam);
	Size_t vlen;
        new_env = S_env_alloc(NULL, nlen, vlen, 2, 1);
    const Size_t nlen = strlen(nam);
    Size_t vlen;
    envstr = S_env_alloc(NULL, nlen, vlen, 2, 1);