[LTP] [PATCH 1/2] add_key05: Avoid race with key garbage collection

[Richard Palethorpe]

The key subsystem independently tracks user info against UID. If a user is
deleted and the UID reused for a new user then the key subsystem will mistake
the new user for the old one.

The keys/keyrings may not be accessible to the new user, but if they are not
yet garbage collected (which happens asynchronously) then the new user may be
exceeding its quota limits.

This results in a race condition where this test can fail because the old
thread keyring is taking up the full quota. We should be able to avoid this by
creating two users in parallel instead of sequentially so that they have
different UIDs.

Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
---
 testcases/kernel/syscalls/add_key/add_key05.c | 36 ++++++++++---------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/testcases/kernel/syscalls/add_key/add_key05.c b/testcases/kernel/syscalls/add_key/add_key05.c
index f64c359bb..5691b8579 100644
--- a/testcases/kernel/syscalls/add_key/add_key05.c
+++ b/testcases/kernel/syscalls/add_key/add_key05.c
@@ -19,8 +19,6 @@
 #include "lapi/keyctl.h"
 
 static char *user_buf;
-static const char *username = "ltp_add_key05";
-static int user_added;
 struct passwd *ltpuser;
 static char fmt[1024];
 
@@ -30,30 +28,29 @@ static const char *const save_restore[] = {
 	NULL,
 };
 
-static void add_user(void)
+static void add_user(char n)
 {
-	if (user_added)
-		return;
-
+	char username[] = "ltp_add_key05_n";
 	const char *const cmd_useradd[] = {"useradd", username, NULL};
 
+	username[sizeof(username) - 2] = '0' + n;
+
 	SAFE_CMD(cmd_useradd, NULL, NULL);
-	user_added = 1;
 	ltpuser = SAFE_GETPWNAM(username);
 	sprintf(fmt, "%5u: %%*5d %%*d/%%*d %%d/%%d %%d/%%d", ltpuser->pw_uid);
+
+	tst_res(TINFO, "Created user %s", ltpuser->pw_name);
 }
 
-static void clean_user(void)
+static void clean_user(char n)
 {
-	if (!user_added)
-		return;
-
+	char username[] = "ltp_add_key05_n";
 	const char *const cmd_userdel[] = {"userdel", "-r", username, NULL};
 
+	username[sizeof(username) - 2] = '0' + n;
+
 	if (tst_cmd(cmd_userdel, NULL, NULL, TST_CMD_PASS_RETVAL))
 		tst_res(TWARN | TERRNO, "'userdel -r %s' failed", username);
-	else
-		user_added = 0;
 }
 
 static inline void parse_proc_key_users(int *used_key, int *max_key, int *used_bytes, int *max_bytes)
@@ -170,7 +167,6 @@ count:
 
 static void do_test(unsigned int n)
 {
-	add_user();
 	if (!SAFE_FORK()) {
 		SAFE_SETUID(ltpuser->pw_uid);
 		TEST(add_key("user", "test1", user_buf, 64, KEY_SPEC_THREAD_KEYRING));
@@ -185,13 +181,21 @@ static void do_test(unsigned int n)
 		exit(0);
 	}
 	tst_reap_children();
-	clean_user();
 }
 
 static void setup(void)
 {
 	SAFE_FILE_PRINTF("/proc/sys/kernel/keys/maxkeys", "200");
 	SAFE_FILE_PRINTF("/proc/sys/kernel/keys/maxbytes", "20000");
+
+	add_user(0);
+	add_user(1);
+}
+
+static void cleanup(void)
+{
+	clean_user(0);
+	clean_user(1);
 }
 
 static struct tst_test test = {
@@ -200,7 +204,7 @@ static struct tst_test test = {
 	.needs_root = 1,
 	.forks_child = 1,
 	.setup = setup,
-	.cleanup = clean_user,
+	.cleanup = cleanup,
 	.save_restore = save_restore,
 	.bufs = (struct tst_buffers []) {
 		{&user_buf, .size = 64},
-- 
2.24.0