[PATCH v3 4/4] read_loose_refs(): treat NULL_SHA1 loose references as broken
- From
Michael Haggerty <mhagger@alum.mit.edu>
- Date
- Jun 3, 2015, 13:51 UTC
- Message-ID
- <eb79f7d96ec74445f7adf62757119273280e09c9.1433339279.git.mhagger@alum.mit.edu>
- In-Reply-To
- <cover.1433339279.git.mhagger@alum.mit.edu>
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@alum.mit.edu> --- 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