[PATCH iptables] xshared: check for maximum buffer length in dd_param_to_argv()

[Pablo Neira Ayuso]

Bail out if we go over the boundary, based on patch from Sebastian.

Reported-by: Sebastian Neef <cont...@0day.work>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---
 iptables/xshared.c | 46 ++++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 18 deletions(-)

diff --git a/iptables/xshared.c b/iptables/xshared.c
index fb186fb1ac65..9434b51a7517 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -433,10 +433,24 @@ void save_argv(void)
        }
 }
 
+struct xt_param {
+       char    buffer[1024];
+       int     len;
+};
+
+static void add_param(struct xt_param *param, const char *curchar)
+{
+       param->buffer[param->len++] = *curchar;
+       if (param->len >= sizeof(param->buffer))
+               xtables_error(PARAMETER_PROBLEM,
+                             "Parameter too long!");
+}
+
 void add_param_to_argv(char *parsestart, int line)
 {
-       int quote_open = 0, escaped = 0, param_len = 0;
-       char param_buffer[1024], *curchar;
+       int quote_open = 0, escaped = 0;
+       struct xt_param param = {};
+       char *curchar;
 
        /* After fighting with strtok enough, here's now
         * a 'real' parser. According to Rusty I'm now no
@@ -445,7 +459,7 @@ void add_param_to_argv(char *parsestart, int line)
        for (curchar = parsestart; *curchar; curchar++) {
                if (quote_open) {
                        if (escaped) {
-                               param_buffer[param_len++] = *curchar;
+                               add_param(&param, curchar);
                                escaped = 0;
                                continue;
                        } else if (*curchar == '\\') {
@@ -455,7 +469,7 @@ void add_param_to_argv(char *parsestart, int line)
                                quote_open = 0;
                                *curchar = '"';
                        } else {
-                               param_buffer[param_len++] = *curchar;
+                               add_param(&param, curchar);
                                continue;
                        }
                } else {
@@ -471,36 +485,32 @@ void add_param_to_argv(char *parsestart, int line)
                case ' ':
                case '\t':
                case '\n':
-                       if (!param_len) {
+                       if (!param.len) {
                                /* two spaces? */
                                continue;
                        }
                        break;
                default:
                        /* regular character, copy to buffer */
-                       param_buffer[param_len++] = *curchar;
-
-                       if (param_len >= sizeof(param_buffer))
-                               xtables_error(PARAMETER_PROBLEM,
-                                             "Parameter too long!");
+                       add_param(&param, curchar);
                        continue;
                }
 
-               param_buffer[param_len] = '\0';
+               param.buffer[param.len] = '\0';
 
                /* check if table name specified */
-               if ((param_buffer[0] == '-' &&
-                    param_buffer[1] != '-' &&
-                    strchr(param_buffer, 't')) ||
-                   (!strncmp(param_buffer, "--t", 3) &&
-                    !strncmp(param_buffer, "--table", strlen(param_buffer)))) {
+               if ((param.buffer[0] == '-' &&
+                    param.buffer[1] != '-' &&
+                    strchr(param.buffer, 't')) ||
+                   (!strncmp(param.buffer, "--t", 3) &&
+                    !strncmp(param.buffer, "--table", strlen(param.buffer)))) {
                        xtables_error(PARAMETER_PROBLEM,
                                      "The -t option (seen in line %u) cannot 
be used in %s.\n",
                                      line, xt_params->program_name);
                }
 
-               add_argv(param_buffer, 0);
-               param_len = 0;
+               add_argv(param.buffer, 0);
+               param.len = 0;
        }
 }
 
-- 
2.11.0