dnsproxy: strip_domains(): fix out of bounds read access

If the name is not found in an answer record then `ptr` is NULL and the
calculation at the end of the while loop `maxlen -= answers - ptr` will
underflow, resulting in a very large `maxlen` value and consequently in
out of bound read accesses parsing beyond the actual end of the answers
section.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/dnsproxy.c b/src/dnsproxy.c
index 4c36cb76..b093e87d 100644
--- a/src/dnsproxy.c
+++ b/src/dnsproxy.c
@@ -1903,6 +1903,8 @@ static int strip_domains(char *name, char *answers, int maxlen)
 				end -= domain_len;
 				maxlen -= domain_len;
 			}
+		} else {
+			ptr = answers;
 		}
 
 		answers += strlen(answers) + 1;