[PATCH] x86: corruption-check: Passing memory_corruption_check to command line causes panic

[zhe.he]

From: He Zhe <zhe.he@xxxxxxxxxxxxx>

memory_corruption_check[{_period|_size}]'s handlers do not check input
argument before passing it to kstrtoul or simple_strtoull. The argument
would be a NULL pointer if each of the kernel parameters, without its
value, is set in command line and thus cause the following panic.

PANIC: early exception 0xe3 IP 10:ffffffff73587c22 error 0 cr2 0x0
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.18-rc8+ #2
[    0.000000] RIP: 0010:kstrtoull+0x2/0x10
...
[    0.000000] Call Trace
[    0.000000]  ? set_corruption_check+0x21/0x49
[    0.000000]  ? do_early_param+0x4d/0x82
[    0.000000]  ? parse_args+0x212/0x330
[    0.000000]  ? rdinit_setup+0x26/0x26
[    0.000000]  ? parse_early_options+0x20/0x23
[    0.000000]  ? rdinit_setup+0x26/0x26
[    0.000000]  ? parse_early_param+0x2d/0x39
[    0.000000]  ? setup_arch+0x2f7/0xbf4
[    0.000000]  ? start_kernel+0x5e/0x4c2
[    0.000000]  ? load_ucode_bsp+0x113/0x12f
[    0.000000]  ? secondary_startup_64+0xa5/0xb0

This patch adds checks to prevent the panic and changes some printk
to right fashion.

Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
---
 arch/x86/kernel/check.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/check.c b/arch/x86/kernel/check.c
index 3339942..d3d65d7 100644
--- a/arch/x86/kernel/check.c
+++ b/arch/x86/kernel/check.c
@@ -31,6 +31,11 @@ static __init int set_corruption_check(char *arg)
 	ssize_t ret;
 	unsigned long val;
 
+	if (!arg) {
+		pr_err("memory_corruption_check: null option\n");
+		return -EINVAL;
+	}
+
 	ret = kstrtoul(arg, 10, &val);
 	if (ret)
 		return ret;
@@ -45,6 +50,11 @@ static __init int set_corruption_check_period(char *arg)
 	ssize_t ret;
 	unsigned long val;
 
+	if (!arg) {
+		pr_err("memory_corruption_check_period: null option\n");
+		return -EINVAL;
+	}
+
 	ret = kstrtoul(arg, 10, &val);
 	if (ret)
 		return ret;
@@ -59,6 +69,11 @@ static __init int set_corruption_check_size(char *arg)
 	char *end;
 	unsigned size;
 
+	if (!arg) {
+		pr_err("memory_corruption_check_size: null option\n");
+		return -EINVAL;
+	}
+
 	size = memparse(arg, &end);
 
 	if (*end == '\0')
@@ -113,7 +128,8 @@ void __init setup_bios_corruption_check(void)
 	}
 
 	if (num_scan_areas)
-		printk(KERN_INFO "Scanning %d areas for low memory corruption\n", num_scan_areas);
+		pr_info("Scanning %d areas for low memory corruption\n",
+			num_scan_areas);
 }
 
 
@@ -132,7 +148,7 @@ void check_for_bios_corruption(void)
 		for (; size; addr++, size -= sizeof(unsigned long)) {
 			if (!*addr)
 				continue;
-			printk(KERN_ERR "Corrupted low memory at %p (%lx phys) = %08lx\n",
+			pr_err("Corrupted low memory at %p (%lx phys) = %08lx\n",
 			       addr, __pa(addr), *addr);
 			corruption = 1;
 			*addr = 0;
@@ -157,7 +173,7 @@ static int start_periodic_check_for_corruption(void)
 	if (!num_scan_areas || !memory_corruption_check || corruption_check_period == 0)
 		return 0;
 
-	printk(KERN_INFO "Scanning for low memory corruption every %d seconds\n",
+	pr_info("Scanning for low memory corruption every %d seconds\n",
 	       corruption_check_period);
 
 	/* First time we run the checks right away */
-- 
2.7.4