Prevent crashes from occurring when reading from data sources with large values

When reading configuration data from an Asterisk .conf file or when pulling
data from an Asterisk RealTime backend, Asterisk was copying the data on the
stack for manipulation. Unfortunately, it is possible to read configuration
data or realtime data from some data source that provides a large blob of
characters. This could potentially cause a crash via a stack overflow.

This patch prevents large sets of data from being read from an ARA backend or
from an Asterisk conf file.

(issue ASTERISK-20658)
Reported by: wdoekes
Tested by: wdoekes, mmichelson
patches:
 * issueA20658_dont_process_overlong_config_lines.patch uploaded by wdoekes (license 5674)
 * issueA20658_func_realtime_limit.patch uploaded by wdoekes (license 5674)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@378375 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/funcs/func_realtime.c b/funcs/func_realtime.c
index a1b6d200eecfa3d607416a2122cee9503f499507..6d7338c7391b5051b5b70641f636e49803cac064 100644 (file)
--- a/funcs/func_realtime.c
+++ b/funcs/func_realtime.c
@@ -219,6 +219,13 @@ static int function_realtime_read(struct ast_channel *chan, const char *cmd, cha
        /* add space for delimiters and final '\0' */
        resultslen += n * (strlen(args.delim1) + strlen(args.delim2)) + 1;
 
+       if (resultslen > len) {
+               ast_log(LOG_WARNING, "Failed to fetch. Realtime data is too large: need %zu, have %zu.\n", resultslen, len);
+               return -1;
+       }
+
+       /* len is going to be sensible, so we don't need to check for stack
+        * overflows here. */
        out = ast_str_alloca(resultslen);
        for (var = head; var; var = var->next)
                ast_str_append(&out, 0, "%s%s%s%s", var->name, args.delim2, var->value, args.delim1);
@@ -439,6 +446,16 @@ static int function_realtime_readdestroy(struct ast_channel *chan, const char *c
        /* add space for delimiters and final '\0' */
        resultslen += n * (strlen(args.delim1) + strlen(args.delim2)) + 1;
 
+       if (resultslen > len) {
+               /* Unfortunately this does mean that we cannot destroy the row
+                * anymore. But OTOH, we're not destroying someones data without
+                * giving him the chance to look at it. */
+               ast_log(LOG_WARNING, "Failed to fetch/destroy. Realtime data is too large: need %zu, have %zu.\n", resultslen, len);
+               return -1;
+       }
+
+       /* len is going to be sensible, so we don't need to check for stack
+        * overflows here. */
        out = ast_str_alloca(resultslen);
        for (var = head; var; var = var->next) {
                ast_str_append(&out, 0, "%s%s%s%s", var->name, args.delim2, var->value, args.delim1);

diff --git a/main/config.c b/main/config.c
index 4a71c1f75c2a1f1a419699c1b4e0718ca7d6f69d..f90cfc1638310bc9f2148e4b2de4e0be131d7424 100644 (file)
--- a/main/config.c
+++ b/main/config.c
@@ -1524,6 +1524,17 @@ static struct ast_config *config_text_file_load(const char *database, const char
                while (!feof(f)) {
                        lineno++;
                        if (fgets(buf, sizeof(buf), f)) {
+                               /* Skip lines that are too long */
+                               if (strlen(buf) == sizeof(buf) - 1 && buf[sizeof(buf) - 1] != '\n') {
+                                       ast_log(LOG_WARNING, "Line %d too long, skipping. It begins with: %.32s...\n", lineno, buf);
+                                       while (fgets(buf, sizeof(buf), f)) {
+                                               if (strlen(buf) != sizeof(buf) - 1 || buf[sizeof(buf) - 1] == '\n') {
+                                                       break;
+                                               }
+                                       }
+                                       continue;
+                               }
+
                                if (ast_test_flag(&flags, CONFIG_FLAG_WITHCOMMENTS) && lline_buffer && ast_str_strlen(lline_buffer)) {
                                        CB_ADD(&comment_buffer, ast_str_buffer(lline_buffer));       /* add the current lline buffer to the comment buffer */
                                        ast_str_reset(lline_buffer);        /* erase the lline buffer */