Re: UBSAN: array-index-out-of-bounds in [...]sound/pci/ctxfi/ctamixer.c:347:48

Salvatore Bonaccorso
2025-11-28T19:32:25Z

Hi Takeshi,

On Fri, Nov 28, 2025 at 06:24:43PM +0100, Takashi Iwai wrote:
> On Fri, 28 Nov 2025 07:07:36 +0100,
> Salvatore Bonaccorso wrote:
> >
> > Hi Jaroslav, hi Takashi
> >
> > A user in Debian reported (in https://bugs.debian.org/1121535) an
> > array-index-out-of-bounds affecting ctxfi/ctamixer.c:
> >
> > On Fri, Nov 28, 2025 at 12:06:07AM +0100, waxhead wrote:
> > > ------------[ cut here ]------------
> > > Nov 27 23:46:53 main kernel: UBSAN: array-index-out-of-bounds in /build/reproducible-path/linux-6.17.8/sound/pci/ctxfi/ctamixer.c:347:48
> > > Nov 27 23:46:53 main kernel: index 8 is out of range for type 'unsigned char [8]'
> > > Nov 27 23:46:53 main kernel: CPU: 4 UID: 0 PID: 468 Comm: (udev-worker) Not tainted 6.17.8+deb14-amd64 #1 PREEMPT(lazy) Debian 6.17.8-1
> > > Nov 27 23:46:53 main kernel: Hardware name: FUJITSU /D3446-S2, BIOS V5.0.0.12 R1.26.0 for D3446-S2x 02/11/2020
> > > Nov 27 23:46:53 main kernel: Call Trace:
> > > Nov 27 23:46:53 main kernel: <TASK>
> > > Nov 27 23:46:53 main kernel: dump_stack_lvl+0x5d/0x80
> > > Nov 27 23:46:53 main kernel: ? __pfx_amixer_set_x+0x10/0x10 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: ubsan_epilogue+0x5/0x2b
> > > Nov 27 23:46:53 main kernel: __ubsan_handle_out_of_bounds.cold+0x54/0x59
> > > Nov 27 23:46:53 main kernel: sum_output_slot+0x44/0x70 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: amixer_set_input+0x4b/0x80 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: amixer_setup+0x1b/0x50 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: ct_mixer_create+0x193/0x570 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: ct_atc_create+0x3cb/0x530 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: ct_card_probe+0x104/0x2c0 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: local_pci_probe+0x3f/0x90
> > > Nov 27 23:46:53 main kernel: pci_device_probe+0xda/0x2b0
> > > Nov 27 23:46:53 main kernel: ? sysfs_do_create_link_sd+0x6d/0xd0
> > > Nov 27 23:46:53 main kernel: really_probe+0xdb/0x340
> > > Nov 27 23:46:53 main kernel: ? pm_runtime_barrier+0x55/0x90
> > > Nov 27 23:46:53 main kernel: __driver_probe_device+0x78/0x140
> > > Nov 27 23:46:53 main kernel: driver_probe_device+0x1f/0xa0
> > > Nov 27 23:46:53 main kernel: ? __pfx___driver_attach+0x10/0x10
> > > Nov 27 23:46:53 main kernel: __driver_attach+0xcb/0x1e0
> > > Nov 27 23:46:53 main kernel: bus_for_each_dev+0x82/0xd0
> > > Nov 27 23:46:53 main kernel: bus_add_driver+0x10b/0x1f0
> > > Nov 27 23:46:53 main kernel: ? __pfx_ct_driver_init+0x10/0x10 [snd_ctxfi]
> > > Nov 27 23:46:53 main kernel: driver_register+0x75/0xe0
> > > Nov 27 23:46:53 main kernel: do_one_initcall+0x58/0x300
> > > Nov 27 23:46:53 main kernel: do_init_module+0x62/0x250
> > > Nov 27 23:46:53 main kernel: ? init_module_from_file+0x8a/0xe0
> > > Nov 27 23:46:53 main kernel: init_module_from_file+0x8a/0xe0
> > > Nov 27 23:46:53 main kernel: idempotent_init_module+0x114/0x310
> > > Nov 27 23:46:53 main kernel: __x64_sys_finit_module+0x6d/0xd0
> > > Nov 27 23:46:53 main kernel: ? syscall_trace_enter+0x8d/0x1d0
> > > Nov 27 23:46:53 main kernel: do_syscall_64+0x82/0x320
> > > Nov 27 23:46:53 main kernel: ? restore_fpregs_from_fpstate+0x46/0xa0
> > > Nov 27 23:46:53 main kernel: ? switch_fpu_return+0x5b/0xe0
> > > Nov 27 23:46:53 main kernel: ? do_syscall_64+0x200/0x320
> > > Nov 27 23:46:53 main kernel: ? exc_page_fault+0x74/0x180
> > > Nov 27 23:46:53 main kernel: entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > > Nov 27 23:46:53 main kernel: RIP: 0033:0x7f77238f3779
> > > Nov 27 23:46:53 main kernel: Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 8b 0d 4f 86 0d 00 f7 d8 64 89 01 48
> > > Nov 27 23:46:53 main kernel: RSP: 002b:00007ffc398103f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
> > > Nov 27 23:46:53 main kernel: RAX: ffffffffffffffda RBX: 000055e0eb622480 RCX: 00007f77238f3779
> > > Nov 27 23:46:53 main kernel: RDX: 0000000000000004 RSI: 00007f77239f744d RDI: 000000000000001b
> > > Nov 27 23:46:53 main kernel: RBP: 0000000000000004 R08: 0000000000000000 R09: 00007f7723ef6280
> > > Nov 27 23:46:53 main kernel: R10: 0000000000000000 R11: 0000000000000246 R12: 00007f77239f744d
> > > Nov 27 23:46:53 main kernel: R13: 0000000000020000 R14: 000055e0eb61e630 R15: 0000000000000000
> > > Nov 27 23:46:53 main kernel: </TASK>
> > > Nov 27 23:46:53 main kernel: ---[ end trace ]---
> >
> > This was specifically with 6.17.8 but up to the current stable 6.17.9
> > there should be no related changes afaics.
>
> Thanks for the report. As a wild guess, a simple fix like below
> should suffice for this case?
>
>
> Takashi
>
> -- 8< --
> --- a/sound/pci/ctxfi/ctamixer.h
> +++ b/sound/pci/ctxfi/ctamixer.h
> @@ -22,7 +22,7 @@
> /* Define the descriptor of a summation node resource */
> struct sum {
> struct rsc rsc; /* Basic resource info */
> - unsigned char idx[8];
> + unsigned char idx[8 + 1]; /* msr + master */
> };
>
> /* Define sum resource request description info */

FWIW, I cannot test this myself. "waxhead", can you please test the
proposed patch and report back if it fixes the issue for you?

Regards,
Salvatore