From b919b4842b42a148ad12754019c58cfc939ae955 Mon Sep 17 00:00:00 2001 From: Macpaul Lin Date: Wed, 17 Oct 2018 23:08:38 +0800 Subject: [PATCH] kgdboc: fix KASAN global-out-of-bounds bug in param_set_kgdboc_var() commit dada6a43b0402eba438a17ac86fdc64ac56a4607 upstream. 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][] dump_bacIctrace+Ox0/0x470 [26364:syz-executor0][] show_stack+0x20/0x30 [26364:syz-executor0][] dump_stack+Oxd8/0x128 [26364:syz-executor0][] print_address_description +0x80/0x4a8 [26364:syz-executor0][] kasan_report+Ox178/0x390 [26364:syz-executor0][] _asan_report_loadi_noabort+Ox18/0x20 [26364:syz-executor0][] param_set_kgdboc_var+Ox194/0x198 [26364:syz-executor0][] param_attr_store+Ox14c/0x270 [26364:syz-executor0][] module_attr_store+0x60/0x90 [26364:syz-executor0][] sysfs_kl_write+Ox100/0x158 [26364:syz-executor0][] kernfs_fop_write+0x27c/0x3a8 [26364:syz-executor0][] do_loop_readv_writev+0x114/0x1b0 [26364:syz-executor0][] do_readv_writev+0x4f8/0x5e0 [26364:syz-executor0][] vfs_writev+0x7c/Oxb8 [26364:syz-executor0][] SyS_writev+Oxcc/0x208 [26364:syz-executor0][] 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 Acked-by: Daniel Thompson Cc: stable Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/kgdboc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index c448225ef5ca..f2b0d8cee8ef 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -232,7 +232,7 @@ 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"); @@ -254,7 +254,7 @@ static int param_set_kgdboc_var(const char *kmessage, struct kernel_param *kp) 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) -- 2.20.1