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

[Takashi Iwai <tiwai@suse.de>]

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 */