[PATCH 1/2] pathspec: use match for sparse-index expansion checks

[tnyman@openai.com]

From: Ted Nyman <tnyman@openai.com>

The pathspec parser computes `len` and `nowildcard_len` from
`item.match`, which includes any prefix added when a command is run
from a subdirectory. `item.original` can still contain the shorter,
unprefixed argument.

Using `item.original + item.nowildcard_len` in
`pathspec_needs_expanded_index()` can therefore read past the end of
the allocation. AddressSanitizer reports a heap-buffer-overflow for
prefixed wildcard pathspecs passed to `git rm` and `git reset` with a
sparse index.

The mismatch dates back to 4d1cfc1351 ("reset: make --mixed
sparse-aware", 2021-11-29), which introduced the helper using
`item.original`. b29ad38322 ("pathspec.h: move
pathspec_needs_expanded_index() from reset.c to here", 2022-08-07)
later moved it to `pathspec.c` and preserved the affected comparisons.

Use `item.match` consistently when checking whether a pathspec can
match a sparse-directory entry. Add coverage for prefixed wildcard
pathspecs so both commands keep the index sparse.

Signed-off-by: Ted Nyman <tnyman@openai.com>
---
 pathspec.c                               | 12 ++++++------
 t/t1092-sparse-checkout-compatibility.sh |  7 +++++++
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/pathspec.c b/pathspec.c
index f78b22709ccb67..281858f21f9c59 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -847,9 +847,9 @@ int pathspec_needs_expanded_index(struct index_state *istate,
 			 * - not-in-cone/bar*: may need expanded index
 			 * - **.c: may need expanded index
 			 */
-			if (strspn(item.original + item.nowildcard_len, "*") ==
+			if (strspn(item.match + item.nowildcard_len, "*") ==
 				    (unsigned int)(item.len - item.nowildcard_len) &&
-			    path_in_cone_mode_sparse_checkout(item.original, istate))
+			    path_in_cone_mode_sparse_checkout(item.match, istate))
 				continue;
 
 			for (pos = 0; pos < istate->cache_nr; pos++) {
@@ -865,7 +865,7 @@ int pathspec_needs_expanded_index(struct index_state *istate,
 				 */
 				if ((unsigned int)item.nowildcard_len >
 					    ce_namelen(ce) &&
-				    !strncmp(item.original, ce->name,
+				    !strncmp(item.match, ce->name,
 					     ce_namelen(ce))) {
 					res = 1;
 					break;
@@ -876,13 +876,13 @@ int pathspec_needs_expanded_index(struct index_state *istate,
 				 * directory and the pathspec does not match the whole
 				 * directory, need to expand the index.
 				 */
-				if (!strncmp(item.original, ce->name, item.nowildcard_len) &&
-				    wildmatch(item.original, ce->name, 0)) {
+				if (!strncmp(item.match, ce->name, item.nowildcard_len) &&
+				    wildmatch(item.match, ce->name, 0)) {
 					res = 1;
 					break;
 				}
 			}
-		} else if (!path_in_cone_mode_sparse_checkout(item.original, istate) &&
+		} else if (!path_in_cone_mode_sparse_checkout(item.match, istate) &&
 			   !matches_skip_worktree(pathspec, i, &skip_worktree_seen))
 			res = 1;
 
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 9814431cd74aff..d0b42371663f9d 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -2119,6 +2119,13 @@ test_expect_success 'sparse index is not expanded: rm' '
 	ensure_not_expanded rm -r deep
 '
 
+test_expect_success 'sparse index is not expanded: prefixed wildcard pathspec' '
+	init_repos &&
+
+	ensure_not_expanded -C deep rm --dry-run -- "a*" &&
+	ensure_not_expanded -C deep reset base -- "a*"
+'
+
 test_expect_success 'grep with and --cached' '
 	init_repos &&