From 08ad56f3f0c1df8f75bac84bcef0d9d0c9b4d20f Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 18 Oct 2012 06:00:12 -0400 Subject: [PATCH] strbuf: always return a non-NULL value from strbuf_detach The current behavior is to return NULL when strbuf did not actually allocate a string. This can be quite surprising to callers, though, who may feed the strbuf from arbitrary data and expect to always get a valid value. In most cases, it does not make a difference because calling any strbuf function will cause an allocation (even if the function ends up not inserting any data). But if the code is structured like: struct strbuf buf = STRBUF_INIT; if (some_condition) strbuf_addstr(&buf, some_string); return strbuf_detach(&buf, NULL); then you may or may not return NULL, depending on the condition. This can cause us to segfault in http-push (when fed an empty URL) and in http-backend (when an empty parameter like "foo=bar&&" is in the $QUERY_STRING). This patch forces strbuf_detach to allocate an empty NUL-terminated string when it is called on a strbuf that has not been allocated. I investigated all call-sites of strbuf_detach. The majority are either not affected by the change (because they call a strbuf_* function unconditionally), or can handle the empty string just as easily as NULL. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- strbuf.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/strbuf.c b/strbuf.c index 5135d5950..5427cfdc6 100644 --- a/strbuf.c +++ b/strbuf.c @@ -44,7 +44,9 @@ void strbuf_release(struct strbuf *sb) char *strbuf_detach(struct strbuf *sb, size_t *sz) { - char *res = sb->alloc ? sb->buf : NULL; + char *res; + strbuf_grow(sb, 0); + res = sb->buf; if (sz) *sz = sb->len; strbuf_init(sb, 0); -- 2.26.2