From 85d6dbdf051d7efdbd1a82fe9e57dc9e8b97d993 Mon Sep 17 00:00:00 2001 From: Xiongfeng Wang Date: Tue, 5 Mar 2019 09:21:25 +0800 Subject: [PATCH] timekeeping: Avoid undefined behaviour in 'ktime_get_with_offset()' euler inclusion category: feature Bugzilla: 10683 CVE: N/A ---------------------------------------- When I ran Syzkaller testsuite, I got the following call trace. Reviewed-by: Yang Yingliang ================================================================================ UBSAN: Undefined behaviour in kernel/time/timekeeping.c:801:8 signed integer overflow: 500152103386 + 9223372036854775807 cannot be represented in type 'long long int' CPU: 6 PID: 13904 Comm: syz-executor.0 Not tainted 4.19.25 #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xca/0x13e lib/dump_stack.c:113 ubsan_epilogue+0xe/0x81 lib/ubsan.c:159 handle_overflow+0x193/0x1e2 lib/ubsan.c:190 ktime_get_with_offset+0x26a/0x2d0 kernel/time/timekeeping.c:801 common_hrtimer_arm+0x14d/0x220 kernel/time/posix-timers.c:817 common_timer_set+0x337/0x530 kernel/time/posix-timers.c:863 do_timer_settime+0x198/0x290 kernel/time/posix-timers.c:892 __do_sys_timer_settime kernel/time/posix-timers.c:918 [inline] __se_sys_timer_settime kernel/time/posix-timers.c:904 [inline] __x64_sys_timer_settime+0x18d/0x260 kernel/time/posix-timers.c:904 do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x462eb9 Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f7968072c58 EFLAGS: 00000246 ORIG_RAX: 00000000000000df RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462eb9 RDX: 00000000200000c0 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f79680736bc R13: 00000000004c54cc R14: 0000000000704278 R15: 00000000ffffffff ================================================================================ It it because global variable 'offsets' is set with a very large but still valid value. It overflows when we add 'tk->tkr_mono.base' with 'offsets'. This patch use 'ktime_add_safe()' to limit the result to 'KTIME_SEC_MAX' when it overflows. Signed-off-by: Xiongfeng Wang Reviewed-by: Yang Yingliang Signed-off-by: Yang Yingliang --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 0073b7151dbb..47950d4eec48 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -798,7 +798,7 @@ ktime_t ktime_get_with_offset(enum tk_offsets offs) do { seq = read_seqcount_begin(&tk_core.seq); - base = ktime_add(tk->tkr_mono.base, *offset); + base = ktime_add_safe(tk->tkr_mono.base, *offset); nsecs = timekeeping_get_ns(&tk->tkr_mono); } while (read_seqcount_retry(&tk_core.seq, seq)); -- GitLab