fix rejection of dns responses with pointers past 512 byte offset

[musl] / src / passwd / getspnam_r.c

diff --git a/src/passwd/getspnam_r.c b/src/passwd/getspnam_r.c
index 9f3378e..541e853 100644 (file)
--- a/src/passwd/getspnam_r.c
+++ b/src/passwd/getspnam_r.c
@@ -12,9 +12,45 @@
  * file. It also avoids any allocation to prevent memory-exhaustion
  * attacks via huge TCB shadow files. */
 
-static long xatol(const char *s)
+static long xatol(char **s)
 {
-       return isdigit(*s) ? atol(s) : -1;
+       long x;
+       if (**s == ':' || **s == '\n') return -1;
+       for (x=0; **s-'0'<10U; ++*s) x=10*x+(**s-'0');
+       return x;
+}
+
+int __parsespent(char *s, struct spwd *sp)
+{
+       sp->sp_namp = s;
+       if (!(s = strchr(s, ':'))) return -1;
+       *s = 0;
+
+       sp->sp_pwdp = ++s;
+       if (!(s = strchr(s, ':'))) return -1;
+       *s = 0;
+
+       s++; sp->sp_lstchg = xatol(&s);
+       if (*s != ':') return -1;
+
+       s++; sp->sp_min = xatol(&s);
+       if (*s != ':') return -1;
+
+       s++; sp->sp_max = xatol(&s);
+       if (*s != ':') return -1;
+
+       s++; sp->sp_warn = xatol(&s);
+       if (*s != ':') return -1;
+
+       s++; sp->sp_inact = xatol(&s);
+       if (*s != ':') return -1;
+
+       s++; sp->sp_expire = xatol(&s);
+       if (*s != ':') return -1;
+
+       s++; sp->sp_flag = xatol(&s);
+       if (*s != '\n') return -1;
+       return 0;
 }
 
 static void cleanup(void *p)
@@ -29,24 +65,25 @@ int getspnam_r(const char *name, struct spwd *sp, char *buf, size_t size, struct
        int rv = 0;
        int fd;
        size_t k, l = strlen(name);
-       char *s;
        int skip = 0;
        int cs;
+       int orig_errno = errno;
 
        *res = 0;
 
        /* Disallow potentially-malicious user names */
        if (*name=='.' || strchr(name, '/') || !l)
-               return EINVAL;
+               return errno = EINVAL;
 
        /* Buffer size must at least be able to hold name, plus some.. */
-       if (size < l+100) return ERANGE;
+       if (size < l+100)
+               return errno = ERANGE;
 
        /* Protect against truncation */
        if (snprintf(path, sizeof path, "/etc/tcb/%s/shadow", name) >= sizeof path)
-               return EINVAL;
+               return errno = EINVAL;
 
-       fd = open(path, O_RDONLY|O_NOFOLLOW|O_NONBLOCK);
+       fd = open(path, O_RDONLY|O_NOFOLLOW|O_NONBLOCK|O_CLOEXEC);
        if (fd >= 0) {
                struct stat st = { 0 };
                errno = EINVAL;
@@ -57,13 +94,19 @@ int getspnam_r(const char *name, struct spwd *sp, char *buf, size_t size, struct
                        return errno;
                }
        } else {
-               f = fopen("/etc/shadow", "rb");
-               if (!f) return errno;
+               if (errno != ENOENT && errno != ENOTDIR)
+                       return errno;
+               f = fopen("/etc/shadow", "rbe");
+               if (!f) {
+                       if (errno != ENOENT && errno != ENOTDIR)
+                               return errno;
+                       return 0;
+               }
        }
 
        pthread_cleanup_push(cleanup, f);
        while (fgets(buf, size, f) && (k=strlen(buf))>0) {
-               if (skip || strncmp(name, buf, l)) {
+               if (skip || strncmp(name, buf, l) || buf[l]!=':') {
                        skip = buf[k-1] != '\n';
                        continue;
                }
@@ -71,37 +114,12 @@ int getspnam_r(const char *name, struct spwd *sp, char *buf, size_t size, struct
                        rv = ERANGE;
                        break;
                }
-               buf[k-1] = 0;
-
-               s = buf;
-               sp->sp_namp = s;
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_pwdp = s;
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_lstchg = xatol(s);
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_min = xatol(s);
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_max = xatol(s);
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_warn = xatol(s);
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_inact = xatol(s);
-               if (!(s = strchr(s, ':'))) continue;
-
-               *s++ = 0; sp->sp_expire = xatol(s);
-               if (!(s = strchr(s, ':'))) continue;
 
-               *s++ = 0; sp->sp_flag = xatol(s);
+               if (__parsespent(buf, sp) < 0) continue;
                *res = sp;
                break;
        }
        pthread_cleanup_pop(1);
+       errno = rv ? rv : orig_errno;
        return rv;
 }