Fix one possible buffer overflow and one underflow. Also some minor

cleanups.  From Jan Kokemueller.  OK deraadt@

1 files changed, 36 insertions, 20 deletions

diff --git a/src/lib/libc/stdlib/realpath.c b/src/lib/libc/stdlib/realpath.c
index c691252ccf..5d226d9abc 100644
--- a/src/lib/libc/stdlib/realpath.c
+++ b/src/lib/libc/stdlib/realpath.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: realpath.c,v 1.21 2016/08/28 04:08:59 guenther Exp $ */
+/*      $OpenBSD: realpath.c,v 1.22 2017/12/24 01:50:50 millert Exp $ */
 /*
  * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
  *
@@ -45,12 +45,19 @@
 char *
 realpath(const char *path, char *resolved)
 {
-        char *p, *q, *s;
-        size_t left_len, resolved_len;
+        const char *p;
+        char *q;
+        size_t left_len, resolved_len, next_token_len;
         unsigned symlinks;
-        int serrno, slen, mem_allocated;
+        int serrno, mem_allocated;
+        ssize_t slen;
         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
 
+        if (path == NULL) {
+                errno = EINVAL;
+                return (NULL);
+        }
+
         if (path[0] == '\0') {
                 errno = ENOENT;
                 return (NULL);
@@ -85,7 +92,7 @@ realpath(const char *path, char *resolved)
                 resolved_len = strlen(resolved);
                 left_len = strlcpy(left, path, sizeof(left));
         }
-        if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
+        if (left_len >= sizeof(left)) {
                 errno = ENAMETOOLONG;
                 goto err;
         }
@@ -99,16 +106,19 @@ realpath(const char *path, char *resolved)
                  * and its length.
                  */
                 p = strchr(left, '/');
-                s = p ? p : left + left_len;
-                if (s - left >= sizeof(next_token)) {
-                        errno = ENAMETOOLONG;
-                        goto err;
+
+                next_token_len = p ? (size_t) (p - left) : left_len;
+                memcpy(next_token, left, next_token_len);
+                next_token[next_token_len] = '\0';
+
+                if (p != NULL) {
+                        left_len -= next_token_len + 1;
+                        memmove(left, p + 1, left_len + 1);
+                } else {
+                        left[0] = '\0';
+                        left_len = 0;
                 }
-                memcpy(next_token, left, s - left);
-                next_token[s - left] = '\0';
-                left_len -= s - left;
-                if (p != NULL)
-                        memmove(left, s + 1, left_len + 1);
+
                 if (resolved[resolved_len - 1] != '/') {
                         if (resolved_len + 1 >= PATH_MAX) {
                                 errno = ENAMETOOLONG;
@@ -136,16 +146,17 @@ realpath(const char *path, char *resolved)
                 }
 
                 /*
-                 * Append the next path component and lstat() it. If
-                 * lstat() fails we still can return successfully if
-                 * there are no more path components left.
+                 * Append the next path component and readlink() it. If
+                 * readlink() fails we still can return successfully if
+                 * it exists but isn't a symlink, or if there are no more
+                 * path components left.
                  */
                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
                 if (resolved_len >= PATH_MAX) {
                         errno = ENAMETOOLONG;
                         goto err;
                 }
-                slen = readlink(resolved, symlink, sizeof(symlink) - 1);
+                slen = readlink(resolved, symlink, sizeof(symlink));
                 if (slen < 0) {
                         switch (errno) {
                         case EINVAL:
@@ -160,6 +171,12 @@ realpath(const char *path, char *resolved)
                         default:
                                 goto err;
                         }
+                } else if (slen == 0) {
+                        errno = EINVAL;
+                        goto err;
+                } else if (slen == sizeof(symlink)) {
+                        errno = ENAMETOOLONG;
+                        goto err;
                 } else {
                         if (symlinks++ > SYMLOOP_MAX) {
                                 errno = ELOOP;
@@ -170,9 +187,8 @@ realpath(const char *path, char *resolved)
                         if (symlink[0] == '/') {
                                 resolved[1] = 0;
                                 resolved_len = 1;
-                        } else if (resolved_len > 1) {
+                        } else {
                                 /* Strip the last path component. */
-                                resolved[resolved_len - 1] = '\0';
                                 q = strrchr(resolved, '/') + 1;
                                 *q = '\0';
                                 resolved_len = q - resolved;