Received-SPF: pass (google.com: domain of linux-wireless-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Hawkins Jiawei <yin31149@gmail.com>
To:     syzbot+473754e5af963cf014cf@syzkaller.appspotmail.com
Cc:     18801353760@163.com, davem@davemloft.net, edumazet@google.com,
        johannes@sipsolutions.net, keescook@chromium.org, kuba@kernel.org,
        linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, pabeni@redhat.com, sfr@canb.auug.org.au,
        syzkaller-bugs@googlegroups.com, yin31149@gmail.com
Subject: Re: [PATCH] Add linux-next specific files for 20220923
Date:   Sun, 25 Sep 2022 00:13:56 +0800
Message-Id: <20220924161357.33193-1-yin31149@gmail.com>
In-Reply-To: <00000000000086d6b205e96e52a7@google.com>
References: <00000000000086d6b205e96e52a7@google.com>
MIME-Version: 1.0
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On Sat, 24 Sept 2022 at 23:55, syzbot <syzbot+473754e5af963cf014cf@syzkaller.appspotmail.com> wrote:
>
> > Hi,
> >
> > On Sat, 24 Sept 2022 at 19:44, Hawkins Jiawei <yin31149@gmail.com> wrote:
> >>
> >> Hi Kees,
> >> On Sat, 24 Sept 2022 at 15:26, Kees Cook <keescook@chromium.org> wrote:
> >> >
> >> > 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. :)
> >> I think this is dynamically sized.
> >>
> >>         hdr_len = compat_event_type_size[descr->header_type];
> >>         event_len = hdr_len + extra_len;
> >>
> >>         [...]
> >>
> >>         /* Add the wireless events in the netlink packet */
> >>         nla = nla_reserve(compskb, IFLA_WIRELESS, event_len);
> >>         if (!nla) {
> >>                 kfree_skb(skb);
> >>                 kfree_skb(compskb);
> >>                 return;
> >>         }
> >>         compat_event = nla_data(nla);
> >>
> >>         [...]
> >>
> >>         if (descr->header_type == IW_HEADER_TYPE_POINT) {
> >>                 compat_wrqu.length = wrqu->data.length;
> >>                 compat_wrqu.flags = wrqu->data.flags;
> >>                 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);
> >>         } else {
> >>                 /* extra_len must be zero, so no if (extra) needed */
> >>                 memcpy(&compat_event->pointer, wrqu,
> >>                         hdr_len - IW_EV_COMPAT_LCP_LEN);
> >>         }
> >>
> >> according to the above code, it seems that this structure is used to
> >> parse ths payload from buffer, so the field **pointer** should just
> >> be a position label to the unused bytes in buffer. Its unused bytes will be
> >> parsed as different structure according to event type.
> >>
> >> >
> >> > >  };
> >> > >  #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);
> >> >                 }
> >> >
> >> I agree with you. It seems that in this situation,
> >> the event type has been cleared, the unuesd bytes start from **pointer**
> >> field should be parsed as struct iw_point type as below, which is a bigger
> >> structure than **pointer**, it will also triggers the memcpy() warning.
> >> /*
> >>          * The problem for 64/32 bit.
> >>          *
> >>          * On 64-bit, a regular event is laid out as follows:
> >>          * An iw_point event is laid out like this instead:
> >>          *      |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
> >>          *      | event.len | event.cmd |     p a d d i n g     |
> >>          *      | iwpnt.len | iwpnt.flg |     p a d d i n g     |
> >>          *      | extra data  ...
> >>          *
> >>          * The second padding exists because struct iw_point is extended,
> >>          * but this depends on the platform...
> >>          *
> >>          * On 32-bit, all the padding shouldn't be there.
> >>          */
> >>
> >> And as for the value of offsetof in calculating **offset**,
> >> I wonder if we can use the macro defined in
> >> include/linux/wireless.h as below, which makes code simplier:
> >> #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
> >>
> >>
> >> >
> >> > >       } 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
> >
> >       hdr_len = compat_event_type_size[descr->header_type];
> >       event_len = hdr_len + extra_len;
> >
> >       [...]
> >
> >       /* Add the wireless events in the netlink packet */
> >       nla = nla_reserve(compskb, IFLA_WIRELESS, event_len);
> >       if (!nla) {
> >               kfree_skb(skb);
> >               kfree_skb(compskb);
> >               return;
> >       }
> >       compat_event = nla_data(nla);
> >
> >       if (descr->header_type == IW_HEADER_TYPE_POINT) {
> >               [...]
> >               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);
> >       } else {
> >               /* extra_len must be zero, so no if (extra) needed */
> >               memcpy(&compat_event->pointer, wrqu,
> >                       hdr_len - IW_EV_COMPAT_LCP_LEN);
> >       }
> >
> >
> > According to above code, it seems that kernel will saves enough memory
> > (hdr_len + extra_len bytes) for payload structure in
> > nla_reserve()(Please correct me if I am wrong), pointed by compat_event.
> > So I wonder if we can use unsafe_memcpy(), to avoid unnecessary
> > memory() check as below, which seems more simple:
> >
> > #syz test git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>
> want 2 args (repo, branch), got 5
>
> >
> > diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> > index 76a80a41615b..a967da647e2b 100644
> > --- a/net/wireless/wext-core.c
> > +++ b/net/wireless/wext-core.c
> > @@ -609,19 +609,26 @@ void wireless_send_event(struct net_device *    dev,
> >
> >       compat_event->len = event_len;
> >       compat_event->cmd = cmd;
> > +
> > +     /* kernel reserves event_len's bytes for compat_event,
> > +      * so we don't need memcpy()'s bounds check
> > +      */
> >       if (descr->header_type == IW_HEADER_TYPE_POINT) {
> >               compat_wrqu.length = wrqu->data.length;
> >               compat_wrqu.flags = wrqu->data.flags;
> > -             memcpy(&compat_event->pointer,
> > +             unsafe_memcpy(&compat_event->pointer,
> >                       ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> > -                     hdr_len - IW_EV_COMPAT_LCP_LEN);
> > +                     hdr_len - IW_EV_COMPAT_LCP_LEN,
> > +                     /* compat_event has enough room */);
> >               if (extra_len)
> > -                     memcpy(((char *) compat_event) + hdr_len,
> > -                             extra, extra_len);
> > +                     unsafe_memcpy(((char *) compat_event) + hdr_len,
> > +                             extra, extra_len,
> > +                             /* compat_event has enough room */);
> >       } else {
> >               /* extra_len must be zero, so no if (extra) needed */
> > -             memcpy(&compat_event->pointer, wrqu,
> > -                     hdr_len - IW_EV_COMPAT_LCP_LEN);
> > +             unsafe_memcpy(&compat_event->pointer, wrqu,
> > +                     hdr_len - IW_EV_COMPAT_LCP_LEN,
> > +                     /* compat_event has enough room */);
> >       }
> >
> >       nlmsg_end(compskb, nlh);

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
master

diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 76a80a41615b..a967da647e2b 100644
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -609,19 +609,26 @@ void wireless_send_event(struct net_device *	dev,
 
 	compat_event->len = event_len;
 	compat_event->cmd = cmd;
+
+	/* kernel reserves event_len's bytes for compat_event,
+	 * so we don't need memcpy()'s bounds check
+	 */
 	if (descr->header_type == IW_HEADER_TYPE_POINT) {
 		compat_wrqu.length = wrqu->data.length;
 		compat_wrqu.flags = wrqu->data.flags;
-		memcpy(&compat_event->pointer,
+		unsafe_memcpy(&compat_event->pointer,
 			((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
-			hdr_len - IW_EV_COMPAT_LCP_LEN);
+			hdr_len - IW_EV_COMPAT_LCP_LEN,
+			/* compat_event has enough room */);
 		if (extra_len)
-			memcpy(((char *) compat_event) + hdr_len,
-				extra, extra_len);
+			unsafe_memcpy(((char *) compat_event) + hdr_len,
+				extra, extra_len,
+				/* compat_event has enough room */);
 	} else {
 		/* extra_len must be zero, so no if (extra) needed */
-		memcpy(&compat_event->pointer, wrqu,
-			hdr_len - IW_EV_COMPAT_LCP_LEN);
+		unsafe_memcpy(&compat_event->pointer, wrqu,
+			hdr_len - IW_EV_COMPAT_LCP_LEN,
+			/* compat_event has enough room */);
 	}
 
 	nlmsg_end(compskb, nlh);