sysctl: move u8 register test to lib/test_sysctl.c

If the test added in commit b5ffbd139688 ("sysctl: move the extra1/2
boundary check of u8 to sysctl_check_table_array") is run as a module, a
lingering reference to the module is left behind, and a 'sysctl -a'
leads to a panic.

To reproduce
    CONFIG_KUNIT=y
    CONFIG_SYSCTL_KUNIT_TEST=m

Then run these commands:
    modprobe sysctl-test
    rmmod sysctl-test
    sysctl -a

The panic varies but generally looks something like this:

    BUG: unable to handle page fault for address: ffffa4571c0c7db4
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    PGD 100000067 P4D 100000067 PUD 100351067 PMD 114f5e067 PTE 0
    Oops: Oops: 0000 [#1] SMP NOPTI
    ... ... ...
    RIP: 0010:proc_sys_readdir+0x166/0x2c0
    ... ... ...
    Call Trace:
     <TASK>
     iterate_dir+0x6e/0x140
     __se_sys_getdents+0x6e/0x100
     do_syscall_64+0x70/0x150
     entry_SYSCALL_64_after_hwframe+0x76/0x7e

Move the test to lib/test_sysctl.c where the registration reference is
handled on module exit

Fixes: b5ffbd139688 ("sysctl: move the extra1/2 boundary check of u8 to sysctl_check_table_array")

Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>

1 files changed, 66 insertions, 0 deletions

diff --git a/lib/test_sysctl.c b/lib/test_sysctl.c
index 4249e0cc8aaf..54a22e4b1346 100644
--- a/lib/test_sysctl.c
+++ b/lib/test_sysctl.c
@@ -37,6 +37,7 @@ static struct {
 	struct ctl_table_header *test_h_mnterror;
 	struct ctl_table_header *empty_add;
 	struct ctl_table_header *empty;
+	struct ctl_table_header *test_u8;
 } sysctl_test_headers;
 
 struct test_sysctl_data {
@@ -239,6 +240,65 @@ static int test_sysctl_run_register_empty(void)
 	return 0;
 }
 
+static const struct ctl_table table_u8_over[] = {
+	{
+		.procname	= "u8_over",
+		.data		= &test_data.uint_0001,
+		.maxlen		= sizeof(u8),
+		.mode		= 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_FOUR,
+		.extra2		= SYSCTL_ONE_THOUSAND,
+	},
+};
+
+static const struct ctl_table table_u8_under[] = {
+	{
+		.procname	= "u8_under",
+		.data		= &test_data.uint_0001,
+		.maxlen		= sizeof(u8),
+		.mode		= 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_NEG_ONE,
+		.extra2		= SYSCTL_ONE_HUNDRED,
+	},
+};
+
+static const struct ctl_table table_u8_valid[] = {
+	{
+		.procname	= "u8_valid",
+		.data		= &test_data.uint_0001,
+		.maxlen		= sizeof(u8),
+		.mode		= 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_TWO_HUNDRED,
+	},
+};
+
+static int test_sysctl_register_u8_extra(void)
+{
+	/* should fail because it's over */
+	sysctl_test_headers.test_u8
+		= register_sysctl("debug/test_sysctl", table_u8_over);
+	if (sysctl_test_headers.test_u8)
+		return -ENOMEM;
+
+	/* should fail because it's under */
+	sysctl_test_headers.test_u8
+		= register_sysctl("debug/test_sysctl", table_u8_under);
+	if (sysctl_test_headers.test_u8)
+		return -ENOMEM;
+
+	/* should not fail because it's valid */
+	sysctl_test_headers.test_u8
+		= register_sysctl("debug/test_sysctl", table_u8_valid);
+	if (!sysctl_test_headers.test_u8)
+		return -ENOMEM;
+
+	return 0;
+}
+
 static int __init test_sysctl_init(void)
 {
 	int err;
@@ -256,6 +316,10 @@ static int __init test_sysctl_init(void)
 		goto out;
 
 	err = test_sysctl_run_register_empty();
+	if (err)
+		goto out;
+
+	err = test_sysctl_register_u8_extra();
 
 out:
 	return err;
@@ -275,6 +339,8 @@ static void __exit test_sysctl_exit(void)
 		unregister_sysctl_table(sysctl_test_headers.empty);
 	if (sysctl_test_headers.empty_add)
 		unregister_sysctl_table(sysctl_test_headers.empty_add);
+	if (sysctl_test_headers.test_u8)
+		unregister_sysctl_table(sysctl_test_headers.test_u8);
 }
 
 module_exit(test_sysctl_exit);