ash: cache more of uid/gid syscalls

Testcase:
setuidgid 1:1 strace ash -c 'test -x TODO; test -x TODO; echo $?'
should show that second "test -x" does not query ids again.

function                                             old     new   delta
ash_main                                            1236    1256     +20
get_cached_euid                                        -      19     +19
get_cached_egid                                        -      19     +19
test_main                                             56      72     +16
test_exec                                            119     135     +16
is_in_supplementary_groups                            52      57      +5
nexpr                                                718     702     -16
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 4/1 up/down: 95/-16)             Total: 79 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/test.c

@@ -638,7 +638,7 @@ static int binop(void)
 static int is_a_group_member(gid_t gid)
 {
 	/* Short-circuit if possible, maybe saving a call to getgroups(). */
-	if (gid == getgid() || gid == getegid())
+	if (gid == get_cached_egid(&groupinfo->egid))
 		return 1;
 
 	return is_in_supplementary_groups(groupinfo, gid);
@@ -656,15 +656,16 @@ static int test_st_mode(struct stat *st, int mode)
 
 //TODO	if (mode == X_OK) {
 //		/* Do we already know with no extra syscalls? */
-//		if (!S_ISREG(st->st_mode))
+//		//if (!S_ISREG(st->st_mode))
-//			return 0; /* not a regular file */
+//		//	return 0; /* not a regular file */
+//		// ^^^ bash does not check this
 //		if ((st->st_mode & ANY_IX) == 0)
 //			return 0; /* no one can execute */
 //		if ((st->st_mode & ANY_IX) == ANY_IX)
 //			return 1; /* anyone can execute */
 //	}
 
-	euid = geteuid();
+	euid = get_cached_euid(&groupinfo->euid);
 	if (euid == 0) {
 		/* Root can read or write any file. */
 		if (mode != X_OK)
@@ -1019,6 +1020,8 @@ int test_main(int argc, char **argv)
 	struct cached_groupinfo info;
 	int r;
 
+	info.euid = -1;
+	info.egid = -1;
 	info.ngroups = 0;
 	info.supplementary_array = NULL;
 	r = test_main2(&info, argc, argv);

include/libbb.h

@@ -1206,11 +1206,13 @@ gid_t *bb_getgroups(int *ngroups, gid_t *group_array) FAST_FUNC;
  * getgroups() is cached in supplementary_array[], to make successive calls faster.
  */
 struct cached_groupinfo {
-	//TODO? gid_t egid;
+	uid_t euid;
+	gid_t egid;
 	int ngroups;
 	gid_t *supplementary_array;
 };
-//TODO? int FAST_FUNC get_cached_egid(gid_t *egid);
+uid_t FAST_FUNC get_cached_euid(uid_t *euid);
+gid_t FAST_FUNC get_cached_egid(gid_t *egid);
 int FAST_FUNC is_in_supplementary_groups(struct cached_groupinfo *groupinfo, gid_t gid);
 
 #if ENABLE_FEATURE_UTMP

libbb/bb_getgroups.c

@@ -46,6 +46,20 @@ gid_t* FAST_FUNC bb_getgroups(int *ngroups, gid_t *group_array)
 	return group_array;
 }
 
+uid_t FAST_FUNC get_cached_euid(uid_t *euid)
+{
+	if (*euid == (uid_t)-1)
+		*euid = geteuid();
+	return *euid;
+}
+
+gid_t FAST_FUNC get_cached_egid(gid_t *egid)
+{
+	if (*egid == (gid_t)-1)
+		*egid = getegid();
+	return *egid;
+}
+
 /* Return non-zero if GID is in our supplementary group list. */
 int FAST_FUNC is_in_supplementary_groups(struct cached_groupinfo *groupinfo, gid_t gid)
 {

shell/ash.c

@@ -536,6 +536,8 @@ extern struct globals_misc *BB_GLOBAL_CONST ash_ptr_to_globals_misc;
 	curdir = nullstr; \
 	physdir = nullstr; \
 	trap_ptr = trap; \
+	groupinfo.euid = -1; \
+	groupinfo.egid = -1; \
 } while (0)
 
 
@@ -2319,7 +2321,7 @@ initvar(void)
 #if ENABLE_FEATURE_EDITING && ENABLE_FEATURE_EDITING_FANCY_PROMPT
 	vps1.var_text = "PS1=\\w \\$ ";
 #else
-	if (!geteuid())
+	if (!get_cached_euid(&groupinfo.euid));
 		vps1.var_text = "PS1=# ";
 #endif
 	vp = varinit;
@@ -13809,14 +13811,13 @@ static int test_exec(/*const char *fullname,*/ struct stat *statb)
 
 	/* Executability depends on our euid/egid/supplementary groups */
 	stmode = S_IXOTH;
-	euid = geteuid();
+	euid = get_cached_euid(&groupinfo.euid);
-//TODO: cache euid?
 	if (euid == 0)
 		/* for root user, any X bit is good enough */
 		stmode = ANY_IX;
 	else if (statb->st_uid == euid)
 		stmode = S_IXUSR;
-	else if (statb->st_gid == getegid())
+	else if (statb->st_gid == get_cached_egid(&groupinfo.egid))
 		stmode = S_IXGRP;
 	else if (is_in_supplementary_groups(&groupinfo, statb->st_gid))
 		stmode = S_IXGRP;