Re: [PATCH] Add linux-next specific files for 20220923

Kees Cook
2022-09-24T07:27:40Z

On Sat, Sep 24, 2022 at 03:10:34PM +0800, Hawkins Jiawei wrote:
> From: Stephen Rothwell <sfr@canb.auug.org.au>
>
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 483fed3b5dc8 Add linux-next specific files for 20220921
> > git tree: linux-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1154ddd5080000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=849cb9f70f15b1ba
> > dashboard link: https://syzkaller.appspot.com/bug?extid=473754e5af963cf014cf
> > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=157c196f080000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11f12618880000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/1cb3f4618323/disk-483fed3b.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/cc02cb30b495/vmlinux-483fed3b.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+473754e5af963cf014cf@syzkaller.appspotmail.com
> >
> > ------------[ cut here ]------------
> > memcpy: detected field-spanning write (size 8) of single field "&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
> > WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623 wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
> > Modules linked in:
> > CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted 6.0.0-rc6-next-20220921-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2022
> > RIP: 0010:wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
> > Code: fa ff ff e8 cd b9 db f8 b9 04 00 00 00 4c 89 e6 48 c7 c2 e0 56 11 8b 48 c7 c7 20 56 11 8b c6 05 94 8e 2a 05 01 e8 b8 b0 a6 00 <0f> 0b e9 9b fa ff ff e8 6f ef 27 f9 e9 a6 fd ff ff e8 c5 ef 27 f9
> > RSP: 0018:ffffc90003b2fbc0 EFLAGS: 00010286
> > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> > RDX: ffff888021d157c0 RSI: ffffffff81620348 RDI: fffff52000765f6a
> > RBP: ffff88801e15c780 R08: 0000000000000005 R09: 0000000000000000
> > R10: 0000000080000000 R11: 20676e696e6e6170 R12: 0000000000000008
> > R13: ffff888025a72640 R14: ffff8880225d402c R15: ffff8880225d4034
> > FS: 0000555556bd9300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007fbda677dfb8 CR3: 000000007b976000 CR4: 00000000003506e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > <TASK>
> > ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
> > wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
> > wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
> > wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
> > wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
> > sock_ioctl+0x285/0x640 net/socket.c:1220
> > vfs_ioctl fs/ioctl.c:51 [inline]
> > __do_sys_ioctl fs/ioctl.c:870 [inline]
> > __se_sys_ioctl fs/ioctl.c:856 [inline]
> > __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7fbda6736af9
> > Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007ffd45e80138 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fbda6736af9
> > RDX: 0000000020000000 RSI: 0000000000008b04 RDI: 0000000000000003
> > RBP: 00007fbda66faca0 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fbda66fad30
> > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> > </TASK>
>
> I think this is the samiliar problem as what Kees Cook pointed out in
> https://lore.kernel.org/linux-next/202209211250.3049C29@keescook/
>
> It seems that memcpy() will performs run-time buffer bounds
> checking, which triggers this warning.
>
> #syz test git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> master
>
>
> diff --git a/include/linux/wireless.h b/include/linux/wireless.h
> index 2d1b54556eff..81603848b0aa 100644
> --- a/include/linux/wireless.h
> +++ b/include/linux/wireless.h
> @@ -26,7 +26,10 @@ struct compat_iw_point {
> struct __compat_iw_event {
> __u16 len; /* Real length of this stuff */
> __u16 cmd; /* Wireless IOCTL */
> - compat_caddr_t pointer;
> + union {
> + compat_caddr_t pointer;
> + __DECLARE_FLEX_ARRAY(__u8, pointer_flex);
> + };

Is this expected to be dynamically sized? I assume so, given the "Real
length" comment. :)

> };
> #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
> #define IW_EV_COMPAT_POINT_OFF offsetof(struct compat_iw_point, length)
> diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> index 76a80a41615b..9d0b50abbe09 100644
> --- a/net/wireless/wext-core.c
> +++ b/net/wireless/wext-core.c
> @@ -620,7 +620,7 @@ void wireless_send_event(struct net_device * dev,

adding in more context code:

memcpy(&compat_event->pointer,
((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
hdr_len - IW_EV_COMPAT_LCP_LEN);
if (extra_len)
memcpy(((char *) compat_event) + hdr_len,
extra, extra_len);

The code above has "pointer" as a memcpy destination as well. I think
that should be changed to pointer_flex as well, as the length calculation
is the same. I wonder what FORTIFY will think about the second memcpy
above. If I'm reading the math correctly, it might need to be:

if (extra_len) {
size_t offset = hdr_len - offsetof(typeof(*compat_event), pointer_flex);
memcpy(&compat_event->pointer_flex[offset], extra, extra_len);
}

> } else {
> /* extra_len must be zero, so no if (extra) needed */
> - memcpy(&compat_event->pointer, wrqu,
> + memcpy(&compat_event->pointer_flex, wrqu,
> hdr_len - IW_EV_COMPAT_LCP_LEN);
> }
>

But otherwise, yes, looks like the right modification. Thanks for tackling
this! It is quite a weird structure! :)

-Kees

--
Kees Cook