[PATCH v4 1/4] printk: Fix panic caused by passing log_buf_len to command line

From: zhe.he
Date: Sat Sep 29 2018 - 10:50:34 EST


From: He Zhe <zhe.he@xxxxxxxxxxxxx>

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

PANIC: early exception 0xe3 IP 10:ffffffffaaeacd0d error 0 cr2 0x0
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #1
[ 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] log_buf_len_setup+0x17/0x22
[ 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/0x4ee
[ 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@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: pmladek@xxxxxxxx
Cc: sergey.senozhatsky@xxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
---
v2:
Split out the addition of pr_fmt and the unsigned update
v3:
Remove error message for NULL pointer
Add check and error message for over 4G use
v4:
Split each piece into one patch

kernel/printk/printk.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9bf5404..06045ab 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1048,7 +1048,12 @@ static void __init log_buf_len_update(unsigned size)
/* save requested log_buf_len since it's too early to process it */
static int __init log_buf_len_setup(char *str)
{
- unsigned size = memparse(str, &str);
+ unsigned int size;
+
+ if (!str)
+ return -EINVAL;
+
+ size = memparse(str, &str);

log_buf_len_update(size);

--
2.7.4