From b70904306fc30857fa3638d2bce7ae0ad1251e23 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Sat, 5 Mar 2016 13:43:30 -0500 Subject: [PATCH] strbuf_getwholeline: NUL-terminate getdelim buffer on error Commit 0cc30e0 (strbuf_getwholeline: use getdelim if it is available, 2015-04-16) tries to clean up after getdelim() returns EOF, but gets one case wrong, which can lead in some obscure cases to us reading uninitialized memory. After getdelim() returns -1, we re-initialize the strbuf only if sb->buf is NULL. The thinking was that either: 1. We fed an existing allocated buffer to getdelim(), and at most it would have realloc'd, leaving our NUL in place. 2. We didn't have a buffer to feed, so we gave getdelim() NULL; sb->buf will remain NULL, and we just want to restore the empty slopbuf. But that second case isn't quite right. getdelim() may allocate a buffer, write nothing into it, and then return EOF. The resulting strbuf rightfully has sb->len set to "0", but is missing the NUL terminator in the first byte. Most call-sites are fine with this. They see the EOF and don't bother looking at the strbuf. Or they notice that sb->len is empty, and don't look at the contents. But there's at least one case that does neither, and relies on parsing the resulting (possibly zero-length) string: fast-import. You can see this in action with the new test (though we probably only notice failure there when run with --valgrind or ASAN). We can fix this by unconditionally resetting the strbuf when we have a buffer after getdelim(). That fixes case 2 above. Case 1 is probably already fine in practice, but it does not hurt for us to re-assert our invariants (especially because we are relying on whatever getdelim() happens to do, which may vary from platform to platform). Our fix covers that case, too. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- strbuf.c | 8 +++++++- t/t9300-fast-import.sh | 4 ++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/strbuf.c b/strbuf.c index d76f0aed85..258650ccb3 100644 --- a/strbuf.c +++ b/strbuf.c @@ -470,9 +470,15 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term) if (errno == ENOMEM) die("Out of memory, getdelim failed"); - /* Restore slopbuf that we moved out of the way before */ + /* + * Restore strbuf invariants; if getdelim left us with a NULL pointer, + * we can just re-init, but otherwise we should make sure that our + * length is empty, and that the result is NUL-terminated. + */ if (!sb->buf) strbuf_init(sb, 0); + else + strbuf_reset(sb); return EOF; } #else diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh index 14a938402e..95c70ed43e 100755 --- a/t/t9300-fast-import.sh +++ b/t/t9300-fast-import.sh @@ -55,6 +55,10 @@ test_expect_success 'empty stream succeeds' ' git fast-import input <<-INPUT_END &&