[PATCH] pretty: avoid buffer overflow in format_person_part

From: Jeff King <peff@peff.net>
Date: May 22, 2012, 05:45 UTC
Message-ID: <20120522054508.GA10576@sigill.intra.peff.net>

When we parse the name and email from a commit to pretty-print them, we usually can just put the result directly into our strbuf result. However, if we are going to use the mailmap, then we must first copy them into a NUL-terminated buffer to feed to the mailmap machinery.

We did so by using strlcpy into a static buffer, but we used it wrong. We fed it the length of the substring we wanted to copy, but never checked that that length was less than the size of the destination buffer.

The simplest fix is to just use snprintf to copy the substring properly while still respecting the destination buffer's size. It might seem like replacing the static buffer with a strbuf would help, but we need to feed a static buffer to the mailmap machinery anyway, so there's not much benefit to handling arbitrary sizes.

A more ideal solution would be for mailmap to grow an interface that:

  1. Takes a pointer and length combination, instead of
     assuming a NUL-terminated string.

  2. Returns a pointer to the mailmap's allocated string,
     rather than copying it into the buffer.

Then we could avoid the need for an extra buffer entirely. However, doing this would involve a lot of refactoring of mailmap and of string_list (which mailmap uses to store the map itself). For now, let's do the simplest thing to fix the bug.

Signed-off-by: Jeff King <peff@peff.net>
---
Current git will not generate commits with names long enough to overflow
here. With my recent series, that is no longer the case. Of course, that
is not really relevant; a malicious attacker is free to craft a bogus
commit directly with hash-object.

 pretty.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/pretty.c b/pretty.c
index 02a0a2b..986e114 100644
--- a/pretty.c
+++ b/pretty.c
@@ -547,8 +547,10 @@ static size_t format_person_part(struct strbuf *sb, char part,
 	mail_end = s.mail_end;
 
 	if (part == 'N' || part == 'E') { /* mailmap lookup */
-		strlcpy(person_name, name_start, name_end - name_start + 1);
-		strlcpy(person_mail, mail_start, mail_end - mail_start + 1);
+		snprintf(person_name, sizeof(person_name), "%.*s",
+			 (int)(name_end - name_start), name_start);
+		snprintf(person_mail, sizeof(person_mail), "%.*s",
+			 (int)(mail_end - mail_start), mail_start);
 		mailmap_name(person_mail, sizeof(person_mail), person_name, sizeof(person_name));
 		name_start = person_name;
 		name_end = name_start + strlen(person_name);

-- 
1.7.9.7.33.gc430a50