Subject: Re: [PATCH v2] wifi: mac80211: Avoid address calculations via out of bounds array indexing

From: Simon Horman <[email-masked]>
Date: Fri, 17 May 2024 21:45:32 +0100

On Fri, May 17, 2024 at 10:54:20AM -0400, Kenton Groombridge wrote:
> req->n_channels must be set before req->channels[] can be used.
> 
> This patch fixes one of the issues encountered in [1].
> 
> [   83.964252] ------------[ cut here ]------------
> [   83.964255] UBSAN: array-index-out-of-bounds in net/mac80211/scan.c:364:4
> [   83.964258] index 0 is out of range for type 'struct ieee80211_channel *[]'
> [   83.964260] CPU: 0 PID: 1695 Comm: iwd Tainted: G           O    T 6.8.9-gentoo-hardened1 #1
> [   83.964262] Hardware name: System76 Pangolin/Pangolin, BIOS ARB928_V00.01_T0025ASY1_ms 04/20/2023
> [   83.964264] Call Trace:
> [   83.964267]  <TASK>
> [   83.964269]  dump_stack_lvl+0x3f/0xc0
> [   83.964274]  __ubsan_handle_out_of_bounds+0xec/0x110
> [   83.964278]  ieee80211_prep_hw_scan+0x2db/0x4b0
> [   83.964281]  __ieee80211_start_scan+0x601/0x990
> [   83.964284]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964287]  ? cfg80211_scan+0x149/0x250
> [   83.964291]  nl80211_trigger_scan+0x874/0x980
> [   83.964295]  genl_family_rcv_msg_doit+0xe8/0x160
> [   83.964298]  genl_rcv_msg+0x240/0x270
> [   83.964301]  ? __cfi_nl80211_trigger_scan+0x10/0x10
> [   83.964302]  ? __cfi_nl80211_post_doit+0x10/0x10
> [   83.964304]  ? __cfi_nl80211_pre_doit+0x10/0x10
> [   83.964307]  ? __cfi_genl_rcv_msg+0x10/0x10
> [   83.964309]  netlink_rcv_skb+0x102/0x130
> [   83.964312]  genl_rcv+0x23/0x40
> [   83.964314]  netlink_unicast+0x23b/0x340
> [   83.964316]  netlink_sendmsg+0x3a9/0x450
> [   83.964319]  __sys_sendto+0x3ae/0x3c0
> [   83.964324]  __x64_sys_sendto+0x21/0x40
> [   83.964326]  do_syscall_64+0x90/0x150
> [   83.964329]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964331]  ? syscall_exit_work+0xc2/0xf0
> [   83.964333]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964335]  ? syscall_exit_to_user_mode+0x74/0xa0
> [   83.964337]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964339]  ? do_syscall_64+0x9c/0x150
> [   83.964340]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964342]  ? syscall_exit_to_user_mode+0x74/0xa0
> [   83.964344]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964346]  ? do_syscall_64+0x9c/0x150
> [   83.964347]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964349]  ? do_syscall_64+0x9c/0x150
> [   83.964351]  ? srso_alias_return_thunk+0x5/0xfbef5
u> [   83.964353]  ? syscall_exit_work+0xc2/0xf0
> [   83.964354]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964356]  ? syscall_exit_to_user_mode+0x74/0xa0
> [   83.964358]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964359]  ? do_syscall_64+0x9c/0x150
> [   83.964361]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964362]  ? do_user_addr_fault+0x488/0x620
> [   83.964366]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964367]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   83.964369]  entry_SYSCALL_64_after_hwframe+0x55/0x5d
> [   83.964372] RIP: 0033:0x6200808578d7
> [   83.964374] Code: 00 00 90 f3 0f 1e fa 41 56 55 41 89 ce 48 83 ec 28 80 3d 7b f7 0d 00 00 74 29 45 31 c9 45 31 c0 41 89 ca b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 71 48 83 c4 28 5d 41 5e c3 66 0f 1f 84 00 00
> [   83.964375] RSP: 002b:0000730c4e821530 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> [   83.964378] RAX: ffffffffffffffda RBX: 000006dbc456c570 RCX: 00006200808578d7
> [   83.964379] RDX: 000000000000005c RSI: 000006dbc45884f0 RDI: 0000000000000004
> [   83.964381] RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
> [   83.964382] R10: 0000000000000000 R11: 0000000000000246 R12: 000006dbc456c480
> [   83.964383] R13: 000006dbc456c450 R14: 0000000000000000 R15: 000006dbc456c610
> [   83.964386]  </TASK>
> [   83.964386] ---[ end trace ]---
> 
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=218810
> 
> v1->v2:
> - Drop changes in cfg80211 as requested by Johannes
> 
> Co-authored-by: Kees Cook <[email-masked]>
> Signed-off-by: Kenton Groombridge <[email-masked]>

Thanks Kenton,

FWWIW, it seems unfortunate to me that the __counted_by field (n_channels)
is set some distance away from the allocation of the flex-array (channels)
whose bounds it checks. It seems it would be pretty easy for a bug in the
code being updated here to result in an overrun.

But in any case, I think this is an improvement and seems correct to me.

Reviewed-by: Simon Horman <[email-masked]>