From dada6a43b0402eba438a17ac86fdc64ac56a4607 Mon Sep 17 00:00:00 2001
From: Macpaul Lin <macpaul@gmail.com>
Date: Wed, 17 Oct 2018 23:08:38 +0800
Subject: [PATCH] kgdboc: fix KASAN global-out-of-bounds bug in param_set_kgdboc_var()
Git-commit: dada6a43b0402eba438a17ac86fdc64ac56a4607
Patch-mainline: v4.20-rc6
References: bsc#1051510
This patch is trying to fix KE issue due to
"bug: KASAN: global-out-of-bounds in param_set_kgdboc_var+0x194/0x198"
reported by Syzkaller scan."
[26364:syz-executor0][name:report8t]BUG: KASAN: global-out-of-bounds in param_set_kgdboc_var+0x194/0x198
[26364:syz-executor0][name:report&]Read of size 1 at addr ffffff900e44f95f by task syz-executor0/26364
[26364:syz-executor0][name:report&]
[26364:syz-executor0]CPU: 7 PID: 26364 Comm: syz-executor0 Tainted: G W 0
[26364:syz-executor0]Call trace:
[26364:syz-executor0][<ffffff9008095cf8>] dump_bacIctrace+Ox0/0x470
[26364:syz-executor0][<ffffff9008096de0>] show_stack+0x20/0x30
[26364:syz-executor0][<ffffff90089cc9c8>] dump_stack+Oxd8/0x128
[26364:syz-executor0][<ffffff90084edb38>] print_address_description +0x80/0x4a8
[26364:syz-executor0][<ffffff90084ee270>] kasan_report+Ox178/0x390
[26364:syz-executor0][<ffffff90084ee4a0>] _asan_report_loadi_noabort+Ox18/0x20
[26364:syz-executor0][<ffffff9008b092ac>] param_set_kgdboc_var+Ox194/0x198
[26364:syz-executor0][<ffffff900813af64>] param_attr_store+Ox14c/0x270
[26364:syz-executor0][<ffffff90081394c8>] module_attr_store+0x60/0x90
[26364:syz-executor0][<ffffff90086690c0>] sysfs_kl_write+Ox100/0x158
[26364:syz-executor0][<ffffff9008666d84>] kernfs_fop_write+0x27c/0x3a8
[26364:syz-executor0][<ffffff9008508264>] do_loop_readv_writev+0x114/0x1b0
[26364:syz-executor0][<ffffff9008509ac8>] do_readv_writev+0x4f8/0x5e0
[26364:syz-executor0][<ffffff9008509ce4>] vfs_writev+0x7c/Oxb8
[26364:syz-executor0][<ffffff900850ba64>] SyS_writev+Oxcc/0x208
[26364:syz-executor0][<ffffff90080883f0>] elO_svc_naked +0x24/0x28
[26364:syz-executor0][name:report&]
[26364:syz-executor0][name:report&]The buggy address belongs to the variable:
[26364:syz-executor0][name:report&] kgdb_tty_line+Ox3f/0x40
[26364:syz-executor0][name:report&]
[26364:syz-executor0][name:report&]Memory state around the buggy address:
[26364:syz-executor0] ffffff900e44f800: 00 00 00 00 00 04 fa fa fa fa fa fa 00 fa fa fa
[26364:syz-executor0] ffffff900e44f880: fa fa fa fa 00 fa fa fa fa fa fa fa 00 fa fa fa
[26364:syz-executor0]> ffffff900e44f900: fa fa fa fa 04 fa fa fa fa fa fa fa 00 00 00 00
[26364:syz-executor0][name:report&] ^
[26364:syz-executor0] ffffff900e44f980: 00 fa fa fa fa fa fa fa 04 fa fa fa fa fa fa fa
[26364:syz-executor0] ffffff900e44fa00: 04 fa fa fa fa fa fa fa 00 fa fa fa fa fa fa fa
[26364:syz-executor0][name:report&]
[26364:syz-executor0][name:panic&]Disabling lock debugging due to kernel taint
[26364:syz-executor0]------------[cut here]------------
After checking the source code, we've found there might be an out-of-bounds
access to "config[len - 1]" array when the variable "len" is zero.
Signed-off-by: Macpaul Lin <macpaul@gmail.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/tty/serial/kgdboc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -250,7 +250,7 @@ static void kgdboc_put_char(u8 chr)
static int param_set_kgdboc_var(const char *kmessage, struct kernel_param *kp)
{
- int len = strlen(kmessage);
+ size_t len = strlen(kmessage);
if (len >= MAX_CONFIG_LEN) {
printk(KERN_ERR "kgdboc: config string too long\n");
@@ -272,7 +272,7 @@ static int param_set_kgdboc_var(const ch
strcpy(config, kmessage);
/* Chop out \n char as a result of echo */
- if (config[len - 1] == '\n')
+ if (len && config[len - 1] == '\n')
config[len - 1] = '\0';
if (configured == 1)