From 814889c28a3ce1bf0bfe2669d43489feba5b4e91 Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Fri, 15 Oct 2021 07:45:38 +0200 Subject: [PATCH] MEDIUM: resolvers: lower-case labels when converting from/to DNS names The whole code relies on performing case-insensitive comparison on lookups, which is extremely inefficient. Let's make sure that all labels to be looked up or sent are first converted to lower case. Doing so is also the opportunity to eliminate an inefficient memcpy() in resolv_dn_label_to_str() that essentially runs over a few unaligned bytes at once. As a side note, that call was dangerous because it relied on a sign-extended size taken from a string that had to be sanitized first. This is tagged medium because while this is 100% safe, it may cause visible changes on the wire at the packet level and trigger bugs in test programs. --- src/resolvers.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/resolvers.c b/src/resolvers.c index 9586f3e47b..6fe38fbe0f 100644 --- a/src/resolvers.c +++ b/src/resolvers.c @@ -1639,9 +1639,9 @@ int resolv_dn_label_to_str(const char *dn, int dn_len, char *str, int str_len) sz = dn[i]; if (i) *ptr++ = '.'; - memcpy(ptr, dn+i+1, sz); - ptr += sz; - i += sz; + /* copy the string at i+1 to lower case */ + for (; sz > 0; sz--) + *(ptr++) = tolower(dn[++i]); } *ptr++ = '\0'; return (ptr - str); @@ -1683,7 +1683,7 @@ int resolv_str_to_dn_label(const char *str, int str_len, char *dn, int dn_len) offset = i+1; continue; } - dn[i+1] = str[i]; + dn[i+1] = tolower(str[i]); } dn[offset] = i - offset; dn[i+1] = '\0'; -- 2.47.3