[PATCH] kernel/dma: Fix panic caused by passing cma to command line

[<zhe.he@windriver.com>]

From: He Zhe <zhe.he@windriver.com>

early_cma does not check input argument before passing it to
simple_strtoull. The argument would be a NULL pointer if "cma", without
its value, is set in command line and thus causes the following panic.

PANIC: early exception 0xe3 IP 10:ffffffffa3e9db8d error 0 cr2 0x0
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc3-yocto-standard+ #7
[    0.000000] RIP: 0010:_parse_integer_fixup_radix+0xd/0x70
...
[    0.000000] Call Trace:
[    0.000000]  simple_strtoull+0x29/0x70
[    0.000000]  memparse+0x26/0x90
[    0.000000]  early_cma+0x17/0x6a
[    0.000000]  do_early_param+0x57/0x8e
[    0.000000]  parse_args+0x208/0x320
[    0.000000]  ? rdinit_setup+0x30/0x30
[    0.000000]  parse_early_options+0x29/0x2d
[    0.000000]  ? rdinit_setup+0x30/0x30
[    0.000000]  parse_early_param+0x36/0x4d
[    0.000000]  setup_arch+0x336/0x99e
[    0.000000]  start_kernel+0x6f/0x4e6
[    0.000000]  x86_64_start_reservations+0x24/0x26
[    0.000000]  x86_64_start_kernel+0x6f/0x72
[    0.000000]  secondary_startup_64+0xa4/0xb0

This patch adds a check to prevent the panic.

Signed-off-by: He Zhe <zhe.he@windriver.com>
Cc: stable@vger.kernel.org
Cc: hch@lst.de
Cc: m.szyprowski@samsung.com
Cc: robin.murphy@arm.com
---
 kernel/dma/contiguous.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 286d823..b2a8790 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -49,7 +49,11 @@ static phys_addr_t limit_cmdline;
 
 static int __init early_cma(char *p)
 {
-	pr_debug("%s(%s)\n", __func__, p);
+	if (!p) {
+		pr_err("Config string not provided\n");
+		return -EINVAL;
+	}
+
 	size_cmdline = memparse(p, &p);
 	if (*p != '@')
 		return 0;
-- 
2.7.4