From a6bbd1d7f5c25b092f143b579860a44e5b0f929e Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@decadent.org.uk>
Date: Fri, 22 Jan 2016 18:02:04 +0000
Subject: [PATCH] Fix potential buffer overflow in entry_to_env
It appears that an entry of type ENTRY_PREFIX with iaid != 1 and an
exclusion can expand to a string of length up to 154 bytes, whereas we
allocate only 144 bytes per entry.
Also, in case of truncation, snprintf() returns the length of the
un-truncated output so we must not use this to increment buf_len.
Finally some of the lengths given to snprintf() are unnecessarily
generous. Reduce them so we don't have to increase the allocated
length per entry further.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
src/script.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)
diff --git a/src/script.c b/src/script.c
index 49f39c4..83fbea5 100644
--- a/src/script.c
+++ b/src/script.c
@@ -157,7 +157,10 @@ static void entry_to_env(const char *name, const void *data, size_t len, enum en
{
size_t buf_len = strlen(name);
const struct odhcp6c_entry *e = data;
- char *buf = realloc(NULL, buf_len + 2 + (len / sizeof(*e)) * 144);
+ // Worst case: ENTRY_PREFIX with iaid != 1 and exclusion
+ const size_t max_entry_len = (INET6_ADDRSTRLEN-1 + 5 + 22 + 15 + 10 +
+ INET6_ADDRSTRLEN-1 + 11 + 1);
+ char *buf = realloc(NULL, buf_len + 2 + (len / sizeof(*e)) * max_entry_len);
memcpy(buf, name, buf_len);
buf[buf_len++] = '=';
@@ -165,28 +168,34 @@ static void entry_to_env(const char *name, const void *data, size_t len, enum en
inet_ntop(AF_INET6, &e[i].target, &buf[buf_len], INET6_ADDRSTRLEN);
buf_len += strlen(&buf[buf_len]);
if (type != ENTRY_HOST) {
- buf_len += snprintf(&buf[buf_len], 6, "/%"PRIu16, e[i].length);
+ snprintf(&buf[buf_len], 6, "/%"PRIu16, e[i].length);
+ buf += strlen(&buf[buf_len]);
if (type == ENTRY_ROUTE) {
buf[buf_len++] = ',';
if (!IN6_IS_ADDR_UNSPECIFIED(&e[i].router)) {
inet_ntop(AF_INET6, &e[i].router, &buf[buf_len], INET6_ADDRSTRLEN);
buf_len += strlen(&buf[buf_len]);
}
- buf_len += snprintf(&buf[buf_len], 24, ",%u", e[i].valid);
- buf_len += snprintf(&buf[buf_len], 12, ",%u", e[i].priority);
+ snprintf(&buf[buf_len], 23, ",%u,%u", e[i].valid, e[i].priority);
+ buf += strlen(&buf[buf_len]);
} else {
- buf_len += snprintf(&buf[buf_len], 24, ",%u,%u", e[i].preferred, e[i].valid);
+ snprintf(&buf[buf_len], 23, ",%u,%u", e[i].preferred, e[i].valid);
+ buf += strlen(&buf[buf_len]);
}
- if (type == ENTRY_PREFIX && ntohl(e[i].iaid) != 1)
- buf_len += snprintf(&buf[buf_len], 16, ",class=%08x", ntohl(e[i].iaid));
+ if (type == ENTRY_PREFIX && ntohl(e[i].iaid) != 1) {
+ snprintf(&buf[buf_len], 16, ",class=%08x", ntohl(e[i].iaid));
+ buf += strlen(&buf[buf_len]);
+ }
if (type == ENTRY_PREFIX && e[i].priority) {
// priority and router are abused for prefix exclusion
- buf_len += snprintf(&buf[buf_len], 12, ",excluded=");
+ snprintf(&buf[buf_len], 11, ",excluded=");
+ buf_len += strlen(&buf[buf_len]);
inet_ntop(AF_INET6, &e[i].router, &buf[buf_len], INET6_ADDRSTRLEN);
buf_len += strlen(&buf[buf_len]);
- buf_len += snprintf(&buf[buf_len], 24, "/%u", e[i].priority);
+ snprintf(&buf[buf_len], 12, "/%u", e[i].priority);
+ buf_len += strlen(&buf[buf_len]);
}
}
buf[buf_len++] = ' ';
--
2.39.5