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midx: fix segfault with no packs and invalid preferred pack 

When asked to write a multi-pack-index the user can specify a preferred
pack that is used as a tie breaker when multiple packs contain the same
objects. When this packfile cannot be found, we just pick the first pack
that is getting tracked by the newly written multi-pack-index as a
fallback.

Picking the fallback can fail in the case where we're asked to write a
multi-pack-index with no packfiles at all: picking the fallback value
will cause a segfault as we blindly index into the array of packfiles,
which would be empty.

Fix this bug by resetting the preferred packfile index to `-1` before
searching for the preferred pack. This fixes the segfault as we already
check for whether the index is `> - 1`. If it is not, we simply don't
pick a preferred packfile at all.

Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt 2023-04-14 08:01:31 +02:00 committed by Junio C Hamano
parent 73876f4861
commit ceb96a160b
2 changed files with 15 additions and 3 deletions
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6
midx.c
View File

@ -1326,17 +1326,17 @@ static int write_midx_internal(const char *object_dir,
}
if (preferred_pack_name) {
int found = 0;
ctx.preferred_pack_idx = -1;
for (i = 0; i < ctx.nr; i++) {
if (!cmp_idx_or_pack_name(preferred_pack_name,
ctx.info[i].pack_name)) {
ctx.preferred_pack_idx = i;
found = 1;
break;
}
}
if (!found)
if (ctx.preferred_pack_idx == -1)
warning(_("unknown preferred pack: '%s'"),
preferred_pack_name);
} else if (ctx.nr &&

12
t/t5319-multi-pack-index.sh
View File

@ -183,6 +183,18 @@ test_expect_success 'write midx with --stdin-packs' '
compare_results_with_midx "mixed mode (one pack + extra)"
test_expect_success 'write with no objects and preferred pack' '
test_when_finished "rm -rf empty" &&
git init empty &&
test_must_fail git -C empty multi-pack-index write \
--stdin-packs --preferred-pack=does-not-exist </dev/null 2>err &&
cat >expect <<-EOF &&
warning: unknown preferred pack: ${SQ}does-not-exist${SQ}
error: no pack files to index.
EOF
test_cmp expect err
'
test_expect_success 'write progress off for redirected stderr' '
git multi-pack-index --object-dir=$objdir write 2>err &&
test_line_count = 0 err