Re: UBSAN: Undefined behaviour in sound/core/timer.c

[Takashi Iwai]

On Sat, 23 Jun 2018 03:13:41 +0200,
air icy wrote:
> 
> Hi,
> This bug was found in Linux Kernel v4.18-rc2
> 1521                                         if (id.subdevice < 0)
> 1522                                                 id.subdevice = 0;
> 1523                                         else
> 1524                                                 id.subdevice++;
> 1525                                 }
> 1526                         }
> 
> $ cat report5
> ================================================================================
> UBSAN: Undefined behaviour in sound/core/timer.c:1524:19
> signed integer overflow:
> 2147483647 + 1 cannot be represented in type 'int'
> CPU: 0 PID: 7737 Comm: syz-executor0 Not tainted 4.18.0-rc1 #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x122/0x1c8 lib/dump_stack.c:113
>  ubsan_epilogue+0x12/0x86 lib/ubsan.c:159
>  handle_overflow+0x1c2/0x21f lib/ubsan.c:190
>  __ubsan_handle_add_overflow+0x2a/0x31 lib/ubsan.c:198
>  snd_timer_user_next_device sound/core/timer.c:1524 [inline]
>  __snd_timer_user_ioctl+0x204d/0x2520 sound/core/timer.c:1939
>  snd_timer_user_ioctl+0x67/0x95 sound/core/timer.c:1994
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  do_vfs_ioctl+0x1e8/0x1340 fs/ioctl.c:686
>  ksys_ioctl+0x9c/0xb0 fs/ioctl.c:701
>  __do_sys_ioctl fs/ioctl.c:708 [inline]
>  __se_sys_ioctl fs/ioctl.c:706 [inline]
>  __x64_sys_ioctl+0x81/0xd0 fs/ioctl.c:706
>  do_syscall_64+0xb8/0x3a0 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x455a09
> Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f9d190edc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f9d190ee6d4 RCX: 0000000000455a09
> RDX: 0000000020000200 RSI: 00000000c0145401 RDI: 0000000000000013
> RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 0000000000000359 R14: 00000000006fa0f8 R15: 0000000000000000
> ================================================================================
> SELinux: unrecognized netlink message: protocol=0 nlmsg_type=7
> sclass=netlink_route_socket pig=7762 comm=syz-executor0
> SELinux: unrecognized netlink message: protocol=0 nlmsg_type=7
> sclass=netlink_route_socket pig=7766 comm=syz-executor0
> sr 1:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
> sr 1:0:0:0: [sr0] tag#0 Sense Key : Illegal Request [current]
> sr 1:0:0:0: [sr0] tag#0 Add. Sense: Invalid command operation code
> sr 1:0:0:0: [sr0] tag#0 CDB: Write(10) 2a 00 00 00 00 00 00 00 40 00
> print_req_error: critical target error, dev sr0, sector 0
> ...
> sr 1:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK
> sr 1:0:0:0: [sr0] tag#0 CDB: Write(16) 8a d0 47 23 7d 8d 1b 64 4d f6 e2 4e
> sr 1:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK
> sr 1:0:0:0: [sr0] tag#0 CDB: Write(16) 8a d0 47 23 7d 8d 1b 64 4d f6 e2 4e
> audit: type=1326 audit(1529712149.140:4): auid=4294967295 uid=0 gid=0
> ses=4294967295 subj=kernel pid=8226 comm="syz-executor1"
> exe="/syz-executor1" sig=31 arch=c000003e syscall=202 compat=0
> ip=0x455a09 code=0x0
> 
> This bug can be repro, if you need it, please tell me.
> 
> bugzilla url: https://bugzilla.kernel.org/show_bug.cgi?id=200213

Thanks for the report.
It looks like nothing too serious but still better to be addressed, of 
course.  Does the patch below cover it?


Takashi

---
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1520,7 +1520,7 @@ static int snd_timer_user_next_device(struct snd_timer_id __user *_tid)
 				} else {
 					if (id.subdevice < 0)
 						id.subdevice = 0;
-					else
+					else if (id.subdevice < INT_MAX)
 						id.subdevice++;
 				}
 			}