Re: Crashes while trying to show tag objects with bad timestamps

[Jeff King <peff@peff.net>]

On Sat, Feb 23, 2013 at 12:30:28AM +0200, Mantas Mikulėnas wrote:

> When messing around with various repositories, I noticed that git 1.8
> (currently using 1.8.2.rc0.22.gb3600c3) has problems parsing tag objects
> that have invalid timestamps.
> 
> Times in tag objects appear to be kept as Unix timestamps, but I didn't
> realize this at first, and ran something roughly equivalent to:
>   git cat-file -p $tagname | git hash-object -w -t tag --stdin
> creating a tag object the "tagger" line containing formatted time
> instead of a Unix timestamp.

Thanks, that makes it easy to replicate. It looks like it is not just
tags, but rather the pp_user_info function does not realize that
split_ident may return NULL for the date field if it is unparseable.
Something like this stops the crash and just gives a bogus date:

diff --git a/pretty.c b/pretty.c
index eae57ad..9688857 100644
--- a/pretty.c
+++ b/pretty.c
@@ -428,8 +428,16 @@ void pp_user_info(const struct pretty_print_context *pp,
 	strbuf_add(&name, namebuf, namelen);
 
 	namelen = name.len + mail.len + 3; /* ' ' + '<' + '>' */
-	time = strtoul(ident.date_begin, &date, 10);
-	tz = strtol(date, NULL, 10);
+
+	if (ident.date_begin) {
+		time = strtoul(ident.date_begin, &date, 10);
+		tz = strtol(date, NULL, 10);
+	}
+	else {
+		/* ident line had malformed date */
+		time = 0;
+		tz = 0;
+	}
 
 	if (pp->fmt == CMIT_FMT_EMAIL) {
 		strbuf_addstr(sb, "From: ");

I guess we should probably issue a warning, too. Also disappointingly,
git-fsck does not seem to detect this breakage at all.

> Git doesn't handle the resulting tag objects nicely at all. For example,
> running `git cat-file -p` on the new object outputs a really odd
> timestamp "Thu Jun Thu Jan 1 00:16:09 1970 +0016" (I'm guessing it
> parses the year as Unix time), and `git show` outright crashes
> (backtrace included below.)

If "cat-file -p" is not using the usual pretty-print routines, it
probably should. I'll take a look.

-Peff