read_all: Drop privileges

The LTP is usually run as root, which allows read_all_dev to read files which
are usually protected from being read at random. This patch introduces the -p
switch to read_all which is used to drop privileges (switch to the nobody
user) for the read_all_dev test.

If -p is set, but the current user does not have the capabilities to change
the uid and gid, then the test will continue under the current user. This
allows the most common scenarios to work as expected, but may cause
difficulties for someone running the LTP under a semi-privileged user.

Signed-off-by: Richard Palethorpe <[email protected]>
Signed-off-by: Cyril Hrubis <[email protected]>

Author: Richard Palethorpe

runtest/fs

@@ -69,7 +69,7 @@ fs_di fs_di -d $TMPDIR
 # Was not sure why it should reside in runtest/crashme and won´t get tested ever
 proc01 proc01 -m 128
 
-read_all_dev read_all -d /dev -e '/dev/watchdog?(0)' -q -r 10
+read_all_dev read_all -d /dev -p -q -r 10
 read_all_proc read_all -d /proc -q -r 10
 read_all_sys read_all -d /sys -q -r 10
 

testcases/kernel/fs/read_all/read_all.c

@@ -50,6 +50,7 @@
 #include <fnmatch.h>
 #include <semaphore.h>
 #include <ctype.h>
+#include <pwd.h>
 
 #include "tst_test.h"
 
@@ -88,6 +89,7 @@ static long worker_count;
 static char *str_max_workers;
 static long max_workers = 15;
 static struct worker *workers;
+static char *drop_privs;
 
 static struct tst_option options[] = {
 	{"v", &verbose,
@@ -104,6 +106,8 @@ static struct tst_option options[] = {
 	 "-w count Set the worker count limit, the default is 15."},
 	{"W:", &str_worker_count,
 	 "-W count Override the worker count. Ignores (-w) and the processor count."},
+	{"p", &drop_privs,
+	 "-p       Drop privileges; switch to the nobody user."},
 	{NULL, NULL, NULL}
 };
 
@@ -247,6 +251,24 @@ static int worker_run(struct worker *self)
 	return 0;
 }
 
+static void maybe_drop_privs(void)
+{
+	struct passwd *nobody;
+
+	if (!drop_privs)
+		return;
+
+	nobody = SAFE_GETPWNAM("nobody");
+
+	TEST(setgid(nobody->pw_gid));
+	if (TEST_RETURN < 0 && TEST_ERRNO != EPERM)
+		tst_brk(TBROK | TTERRNO, "Failed to use nobody gid");
+
+	TEST(setuid(nobody->pw_uid));
+	if (TEST_RETURN < 0 && TEST_ERRNO != EPERM)
+		tst_brk(TBROK | TTERRNO, "Failed to use nobody uid");
+}
+
 static void spawn_workers(void)
 {
 	int i;
@@ -257,8 +279,10 @@ static void spawn_workers(void)
 	for (i = 0; i < worker_count; i++) {
 		wa[i].q = queue_init();
 		wa[i].pid = SAFE_FORK();
-		if (!wa[i].pid)
+		if (!wa[i].pid) {
+			maybe_drop_privs();
 			exit(worker_run(wa + i));
+		}
 	}
 }