sha1_file: guard against invalid loose subdirectory numbers

Loose object subdirectories have hexadecimal names based on the first
byte of the hash of contained objects, thus their numerical
representation can range from 0 (0x00) to 255 (0xff).  Change the type
of the corresponding variable in for_each_file_in_obj_subdir() and
associated callback functions to unsigned int and add a range check.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fsck.c

@@ -537,7 +537,7 @@ static int fsck_cruft(const char *basename, const char *path, void *data)
 	return 0;
 }
 
-static int fsck_subdir(int nr, const char *path, void *progress)
+static int fsck_subdir(unsigned int nr, const char *path, void *progress)
 {
 	display_progress(progress, nr + 1);
 	return 0;

builtin/prune-packed.c

@@ -10,7 +10,7 @@ static const char * const prune_packed_usage[] = {
 
 static struct progress *progress;
 
-static int prune_subdir(int nr, const char *path, void *data)
+static int prune_subdir(unsigned int nr, const char *path, void *data)
 {
 	int *opts = data;
 	display_progress(progress, nr + 1);

builtin/prune.c

@@ -68,7 +68,7 @@ static int prune_cruft(const char *basename, const char *path, void *data)
 	return 0;
 }
 
-static int prune_subdir(int nr, const char *path, void *data)
+static int prune_subdir(unsigned int nr, const char *path, void *data)
 {
 	if (!show_only)
 		rmdir(path);

cache.h

@@ -1805,10 +1805,10 @@ typedef int each_loose_object_fn(const struct object_id *oid,
 typedef int each_loose_cruft_fn(const char *basename,
 				const char *path,
 				void *data);
-typedef int each_loose_subdir_fn(int nr,
+typedef int each_loose_subdir_fn(unsigned int nr,
 				 const char *path,
 				 void *data);
-int for_each_file_in_obj_subdir(int subdir_nr,
+int for_each_file_in_obj_subdir(unsigned int subdir_nr,
 				struct strbuf *path,
 				each_loose_object_fn obj_cb,
 				each_loose_cruft_fn cruft_cb,

sha1_file.c

@@ -3735,7 +3735,7 @@ void assert_sha1_type(const unsigned char *sha1, enum object_type expect)
 		    typename(expect));
 }
 
-int for_each_file_in_obj_subdir(int subdir_nr,
+int for_each_file_in_obj_subdir(unsigned int subdir_nr,
 				struct strbuf *path,
 				each_loose_object_fn obj_cb,
 				each_loose_cruft_fn cruft_cb,
@@ -3747,6 +3747,9 @@ int for_each_file_in_obj_subdir(int subdir_nr,
 	struct dirent *de;
 	int r = 0;
 
+	if (subdir_nr > 0xff)
+		BUG("invalid loose object subdirectory: %x", subdir_nr);
+
 	origlen = path->len;
 	strbuf_complete(path, '/');
 	strbuf_addf(path, "%02x", subdir_nr);