NULL_SHA1 is used to indicate of "invalid SHA-1" throughout our code
(and the code of other git implementations), so it is vastly more
likely that a reference was set to this value due to a software bug
than that NULL_SHA1 is the legitimate SHA-1 of an actual object.
Therefore, if a loose reference has the value NULL_SHA1, consider it
to be broken.
Amusingly, each of the other 2^160-1 possible SHA-1 values is exactly
as unlikely as NULL_SHA1 to be the SHA-1 of an actual object. The
difference is that most of those other values are also very unlikely
to be written to a loose reference file by accident, whereas
accidentally writing NULL_SHA1 to a loose reference file would be an
easy mistake to make.
Signed-off-by: Michael Haggerty <mhagger@xxxxxxxxxxxx>
---
refs.c | 10 ++++++++++
t/t6301-for-each-ref-errors.sh | 2 +-
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/refs.c b/refs.c
index 6736424..83af13d 100644
--- a/refs.c
+++ b/refs.c
@@ -1324,6 +1324,16 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
if (!read_ok) {
hashclr(sha1);
flag |= REF_ISBROKEN;
+ } else if (is_null_sha1(sha1)) {
+ /*
+ * It is so astronomically unlikely
+ * that NULL_SHA1 is the SHA-1 of an
+ * actual object that we consider its
+ * appearance in a loose reference
+ * file to be repo corruption
+ * (probably due to a software bug).
+ */
+ flag |= REF_ISBROKEN;
}
if (check_refname_format(refname.buf,
diff --git a/t/t6301-for-each-ref-errors.sh b/t/t6301-for-each-ref-errors.sh
index 72d2397..cdb67a0 100755
--- a/t/t6301-for-each-ref-errors.sh
+++ b/t/t6301-for-each-ref-errors.sh
@@ -24,7 +24,7 @@ test_expect_success 'Broken refs are reported correctly' '
test_cmp broken-err err
'
-test_expect_failure 'NULL_SHA1 refs are reported correctly' '
+test_expect_success 'NULL_SHA1 refs are reported correctly' '
r=refs/heads/zeros &&
echo $ZEROS >.git/$r &&
test_when_finished "rm -f .git/$r" &&
--
2.1.4
--
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