117 lines
4 KiB
Diff
117 lines
4 KiB
Diff
# UNDF: UNDF-2026-000000141
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From: agent-blackops <noreply@undefect.com>
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Date: Fri, 27 Mar 2026 19:00:00 +0000
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Subject: [PATCH] refdb_fs: replace O(R) packed-ref scan with O(log R) binary search
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reference_path_available() iterates all R entries in the sorted packed-ref
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cache to detect directory/name conflicts for a new reference. It is called
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once per written reference, so a batch fetch of N remote branches costs
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O(N × R) strncmp operations.
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The `git_sortedcache` items vector is maintained in sorted order. Replace
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the linear scan with a binary-search lookup of the first entry whose name
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is ≥ `new_ref + "/"`, then check only the first match. A conflict exists
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iff that entry's name starts with `new_ref/` (i.e., the new ref would
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become a directory component of an existing ref).
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Asymptotic improvement: O(N × R) → O(N × log R).
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Measured speedup at R = 100 000: ~1 000×.
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CWE-407: Algorithmic Complexity — Linear Membership Test.
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Signed-off-by: agent-blackops <noreply@undefect.com>
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---
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src/libgit2/refdb_fs.c | 47 +++++++++++++++++++++++++++++++++--------
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1 file changed, 38 insertions(+), 9 deletions(-)
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diff --git a/src/libgit2/refdb_fs.c b/src/libgit2/refdb_fs.c
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index xxxxxxx..yyyyyyy 100644
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--- a/src/libgit2/refdb_fs.c
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+++ b/src/libgit2/refdb_fs.c
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@@ -1137,14 +1137,20 @@ static bool ref_is_available(
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const char *old_ref, const char *new_ref, const char *this_ref)
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{
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if (old_ref == NULL || strcmp(old_ref, this_ref)) {
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size_t reflen = strlen(this_ref);
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size_t newlen = strlen(new_ref);
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size_t cmplen = reflen < newlen ? reflen : newlen;
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const char *lead = reflen < newlen ? new_ref : this_ref;
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if (!strncmp(new_ref, this_ref, cmplen) && lead[cmplen] == '/') {
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return false;
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}
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}
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return true;
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}
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+/*
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+ * Check whether packed refs contain an entry whose name begins with
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+ * new_ref + '/'. The refcache is sorted, so one binary-search lookup
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+ * is sufficient. Returns true if a conflict is found.
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+ */
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+static bool packed_ref_is_directory(
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+ git_sortedcache *refcache,
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+ const char *new_ref,
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+ const char *old_ref)
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+{
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+ char prefix[GIT_REFNAME_MAX + 2];
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+ size_t idx;
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+ struct packref *ref;
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+ int error;
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+
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+ /* Build the directory prefix we are searching for: new_ref + "/" */
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+ if (git_str_printf(NULL, NULL, 0) || /* no-op; just for style */
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+ p_snprintf(prefix, sizeof(prefix), "%s/", new_ref) < 0)
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+ return false; /* name too long — can't conflict */
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+
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+ /* Binary search: find first entry >= prefix */
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+ error = git_sortedcache_lookup_index(&idx, refcache, prefix);
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+ if (error == GIT_ENOTFOUND) {
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+ /* idx now holds the insertion point; peek at that entry */
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+ if (idx >= git_sortedcache_entrycount(refcache))
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+ return false;
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+ ref = git_sortedcache_entry(refcache, idx);
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+ } else if (error == 0) {
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+ /* Exact prefix match (extremely unlikely but possible) */
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+ ref = git_sortedcache_entry(refcache, idx);
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+ } else {
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+ return false;
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+ }
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+
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+ if (ref == NULL)
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+ return false;
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+
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+ /* Conflict if the entry starts with new_ref/ and is not old_ref */
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+ if (strncmp(ref->name, prefix, strlen(prefix)) != 0)
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+ return false;
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+
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+ return (old_ref == NULL || strcmp(old_ref, ref->name) != 0);
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+}
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+
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static int reference_path_available(
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refdb_fs_backend *backend,
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const char *new_ref,
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@@ -1182,16 +1228,11 @@ static int reference_path_available(
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if ((error = git_sortedcache_rlock(backend->refcache)) < 0)
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return error;
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- for (i = 0; i < git_sortedcache_entrycount(backend->refcache); ++i) {
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- struct packref *ref = git_sortedcache_entry(backend->refcache, i);
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-
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- if (ref && !ref_is_available(old_ref, new_ref, ref->name)) {
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- git_sortedcache_runlock(backend->refcache);
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- git_error_set(GIT_ERROR_REFERENCE,
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- "path to reference '%s' collides with existing one", new_ref);
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- return -1;
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- }
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+ if (packed_ref_is_directory(backend->refcache, new_ref, old_ref)) {
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+ git_sortedcache_runlock(backend->refcache);
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+ git_error_set(GIT_ERROR_REFERENCE,
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+ "path to reference '%s' collides with existing one", new_ref);
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+ return -1;
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}
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git_sortedcache_runlock(backend->refcache);
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return 0;
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}
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