From 9903253c347f9e0bffd285ae3829aef251cc852d Mon Sep 17 00:00:00 2001
From: hopper-vul <118949689+hopper-vul@users.noreply.github.com>
Date: Wed, 18 Jan 2023 22:14:26 +0800
Subject: [PATCH] Add str len check in config_sortlist to avoid stack overflow
 (#497)

In ares_set_sortlist, it calls config_sortlist(..., sortstr) to parse
the input str and initialize a sortlist configuration.

However, ares_set_sortlist has not any checks about the validity of the input str.
It is very easy to create an arbitrary length stack overflow with the unchecked
`memcpy(ipbuf, str, q-str);` and `memcpy(ipbufpfx, str, q-str);`
statements in the config_sortlist call, which could potentially cause severe
security impact in practical programs.

This commit add necessary check for `ipbuf` and `ipbufpfx` which avoid the
potential stack overflows.

fixes #496

Fix By: @hopper-vul
---
 ares_init.c            | 4 ++++
 test/ares-test-init.cc | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/ares_init.c b/ares_init.c
index f7b700b..5aad7c8 100644
--- a/ares_init.c
+++ b/ares_init.c
@@ -2065,6 +2065,8 @@ static int config_sortlist(struct apattern **sortlist, int *nsort,
       q = str;
       while (*q && *q != '/' && *q != ';' && !ISSPACE(*q))
         q++;
+      if (q-str >= 16)
+        return ARES_EBADSTR;
       memcpy(ipbuf, str, q-str);
       ipbuf[q-str] = '\0';
       /* Find the prefix */
@@ -2073,6 +2075,8 @@ static int config_sortlist(struct apattern **sortlist, int *nsort,
           const char *str2 = q+1;
           while (*q && *q != ';' && !ISSPACE(*q))
             q++;
+          if (q-str >= 32)
+            return ARES_EBADSTR;
           memcpy(ipbufpfx, str, q-str);
           ipbufpfx[q-str] = '\0';
           str = str2;
diff --git a/test/ares-test-init.cc b/test/ares-test-init.cc
index 63c6a22..ee84518 100644
--- a/test/ares-test-init.cc
+++ b/test/ares-test-init.cc
@@ -275,6 +275,8 @@ TEST_F(DefaultChannelTest, SetAddresses) {
 
 TEST_F(DefaultChannelTest, SetSortlistFailures) {
   EXPECT_EQ(ARES_ENODATA, ares_set_sortlist(nullptr, "1.2.3.4"));
+  EXPECT_EQ(ARES_EBADSTR, ares_set_sortlist(channel_, "111.111.111.111*/16"));
+  EXPECT_EQ(ARES_EBADSTR, ares_set_sortlist(channel_, "111.111.111.111/255.255.255.240*"));
   EXPECT_EQ(ARES_SUCCESS, ares_set_sortlist(channel_, "xyzzy ; lwk"));
   EXPECT_EQ(ARES_SUCCESS, ares_set_sortlist(channel_, "xyzzy ; 0x123"));
 }
-- 
2.37.3