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refs/ref-cache: fix SEGFAULT when seeking in empty directories

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The 'cache_ref_iterator_seek()' function is used to seek the
`ref_iterator` to the desired reference in the ref-cache mechanism. We
use the seeking functionality to implement the '--start-after' flag in
'git-for-each-ref(1)'.

When using the files-backend with packed-refs, it is possible that some
of the refs directories are empty. For e.g. just after repacking, the
'refs/heads' directory would be empty. The ref-cache seek mechanism,
doesn't take this into consideration when descending into a
subdirectory, and makes an out of bounds access, causing SEGFAULT as we
try to access entries within the directory. Fix this by breaking out of
the loop when we enter an empty directory.

Since we start with the base directory of 'refs/' which is never empty,
it is okay to perform this check after the first iteration in the
`do..while` clause.

Add tests which simulate this behavior and also provide coverage over
using the feature over packed-refs.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Karthik Nayak
2025-10-01 14:17:29 +02:00
committed by Junio C Hamano
parent 821f583da6
commit 351c6e719a
2 changed files with 66 additions and 1 deletions
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2
refs/ref-cache.c
View File

@@ -539,7 +539,7 @@ static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
*/
break;
}
} while (slash);
} while (slash && dir->nr);
}
return 0;

65
t/t6302-for-each-ref-filter.sh
View File

@@ -754,4 +754,69 @@ test_expect_success 'start after used with custom sort order' '
test_cmp expect actual
'
test_expect_success 'start after with packed refs' '
test_when_finished "rm -rf repo" &&
git init repo &&
(
cd repo &&
test_commit default &&
git update-ref --stdin <<-\EOF &&
create refs/heads/branch @
create refs/heads/side @
create refs/odd/spot @
create refs/tags/one @
create refs/tags/two @
commit
EOF
cat >expect <<-\EOF &&
refs/tags/default
refs/tags/one
refs/tags/two
EOF
git pack-refs --all &&
git for-each-ref --format="%(refname)" --start-after=refs/odd/spot >actual &&
test_cmp expect actual
)
'
test_expect_success 'start after with packed refs and some loose refs' '
test_when_finished "rm -rf repo" &&
git init repo &&
(
cd repo &&
test_commit default &&
git update-ref --stdin <<-\EOF &&
create refs/heads/branch @
create refs/heads/side @
create refs/odd/spot @
create refs/tags/one @
create refs/tags/two @
commit
EOF
git pack-refs --all &&
git update-ref --stdin <<-\EOF &&
create refs/heads/foo @
create refs/odd/tee @
commit
EOF
cat >expect <<-\EOF &&
refs/odd/tee
refs/tags/default
refs/tags/one
refs/tags/two
EOF
git for-each-ref --format="%(refname)" --start-after=refs/odd/spot >actual &&
test_cmp expect actual
)
'
test_done