It was reported that using git-pull(1) in a repository whose remote
contains branches with emojis leads to the following bug:
$ git pull
remote: Enumerating objects: 161255, done.
remote: Counting objects: 100% (55884/55884), done.
remote: Compressing objects: 100% (5518/5518), done.
remote: Total 161255 (delta 54253), reused 50509 (delta 50364),
pack-reused 105371 (from 4)
Receiving objects: 100% (161255/161255), 309.90 MiB | 16.87 MiB/s, done.
Resolving deltas: 100% (118048/118048), completed with 13416 local objects.
From github.com:github/github
97ab7ae3f3745..8fb2f9fa180ed master -> origin/master
[...snip many screenfuls of updates to origin remotes...]
BUG: refs/packed-backend.c:984: packed-refs backend yielded reference
preceding its prefix
error: fetch died of signal 6
This issue bisects to 22600c04529 (refs/iterator: implement seeking for
packed-ref iterators, 2025-03-12) where we have implemented seeking for
the packed-ref iterator. As part of that change we introduced a check
that verifies that the iterator only returns refnames bigger than the
prefix. In theory, this check should always hold: when a prefix is set
we know that we would've seeked that prefix first, so we should never
see a reference sorting before that prefix.
But in practice the check itself is misbehaving when handling unicode
characters. The particular issue triggered with a branch that got the
"shaved ice" unicode character in its name, which is composed of the
bytes "0xEE 0x90 0xBF". The bug triggers when we compare the refname
"refs/heads/<shaved-ice>" to something like "refs/heads/z", and it
specifically hits when comparing the first byte, "0xEE".
The root cause is that the most-significant bit of 0xEE is set. The
`refname` and `prefix` pointers that we use to compare bytes with one
another are both pointers to signed characters. As such, when we
dereference the 0xEE byte the result is a _negative_ value, and this
value will of course compare smaller than "z".
We can see that this issue is avoided in `cmp_packed_refname()`, where
we explicitly cast each byte to its unsigned form. Fix the bug by doing
the same in `packed_ref_iterator_advance()`.
Reported-by: Elijah Newren <newren@xxxxxxxxx>
Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
---
Hi,
this patch addresses the issue reported by Elijah at [1]. Thanks!
Patrick
[1]: <CABPp-BFBqC_t5QSexRQpYsqXBa11WK+OqGt167E=K=xod=buQw@xxxxxxxxxxxxxx>
---
refs/packed-backend.c | 4 ++--
t/t1408-packed-refs.sh | 15 +++++++++++++++
2 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index b4289a7d9ce..7e31904bd41 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -980,9 +980,9 @@ static int packed_ref_iterator_advance(struct ref_iterator *ref_iterator)
continue;
while (prefix && *prefix) {
- if (*refname < *prefix)
+ if ((unsigned char)*refname < (unsigned char)*prefix)
BUG("packed-refs backend yielded reference preceding its prefix");
- else if (*refname > *prefix)
+ else if ((unsigned char)*refname > (unsigned char)*prefix)
return ITER_DONE;
prefix++;
refname++;
diff --git a/t/t1408-packed-refs.sh b/t/t1408-packed-refs.sh
index 41ba1f1d7fc..833477f0fa3 100755
--- a/t/t1408-packed-refs.sh
+++ b/t/t1408-packed-refs.sh
@@ -42,4 +42,19 @@ test_expect_success 'no error from stale entry in packed-refs' '
test_cmp expect actual
'
+test_expect_success 'list packed refs with unicode characters' '
+ test_when_finished "rm -rf repo" &&
+ git init repo &&
+ (
+ cd repo &&
+ test_commit --no-tag A &&
+ git update-ref refs/heads/ HEAD &&
+ git update-ref refs/heads/z HEAD &&
+ git pack-refs --all &&
+ printf "%s commit\trefs/heads/z\n" $(git rev-parse HEAD) >expect &&
+ git for-each-ref refs/heads/z >actual &&
+ test_cmp expect actual
+ )
+'
+
test_done
---
base-commit: 5b97a56fa0e7d580dc8865b73107407c9b3f0eff
change-id: 20250404-b4-pks-packed-backend-seek-with-utf8-668c182ddcf7
