Prevent git blame from segfaulting on a missing author name

The author name should never be missing in a valid commit, but git shouldn't segfault no matter what is in the object database.

---
git blame was segfaulting on a repro produced by piping mtn git_export from the Pidgin repository to git fast-import. This was the most obvious fix, but I'm not sure if it is the best solution.

Here's a script that reproduces the segfault.

#!/bin/sh
set -e
git init
echo line > afile
git add afile
TREE=git write-tree
cat >badcommit <<EOF
tree $TREE
author <noname> 1234567890 +0000
committer David Reiss <[email protected]> 1234567890 +0000

some message
EOF
COMMIT=git hash-object -t commit -w badcommit
echo "git --no-pager blame $COMMIT -- afile"
git --no-pager blame $COMMIT -- afile

 builtin-blame.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index d4e25a5..5e19c79 100644
@@ -1326,7 +1326,7 @@ static void get_ac_line(const char *inbuf, const char *what,
 	timepos = tmp;
 
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (tmp > person && *tmp != ' ')
 		tmp--;
 	mailpos = tmp + 1;
 	*tmp = 0;

1.6.3.3

Thanks.

While it is _unusual_ not to have a human readable name, if the commits come from foreign systems (e.g. CVS/SVN), there often are not sufficient information in the source to fabricate names, so we should tolerate them.

We might want to also teach fast-import to warn when asked (i.e. when we are feeding from a foreign interface that is designed to read from a source that is capable of recording real names), but we shouldn't prevent it from creating such a commit.

Please make that into a new test in an existing test suite somewhere in t/ directory.

I think we probably should prepare ourselves to be fed with even more broken commits, perhaps like this, if we are fixing it..

 builtin-blame.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

index d4e25a5..14830a3 100644
@@ -1305,6 +1305,7 @@ static void get_ac_line(const char *inbuf, const char *what,
 	error_out:
 		/* Ugh */
 		*tz = "(unknown)";
+		strcpy(person, *tz);
 		strcpy(mail, *tz);
 		*time = 0;
 		return;

@@ -1314,20 +1315,26 @@ static void get_ac_line(const char *inbuf, const char *what,
 	tmp = person;
 	tmp += len;
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (person < tmp && *tmp != ' ')
 		tmp--;
+	if (tmp == person)
+		goto error_out;
 	*tz = tmp+1;
 	tzlen = (person+len)-(tmp+1);
 
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (person < tmp && *tmp != ' ')
 		tmp--;
+	if (tmp == person)
+		goto error_out;
 	*time = strtoul(tmp, NULL, 10);
 	timepos = tmp;
 
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (person < tmp && *tmp != ' ')
 		tmp--;
+	if (tmp <= person)
+		return;
 	mailpos = tmp + 1;
 	*tmp = 0;
 	maillen = timepos - tmp;