Hi, On Sat, 24 Sept 2022 at 19:44, Hawkins Jiawei <yin31149@xxxxxxxxx> wrote: > > Hi Kees, > On Sat, 24 Sept 2022 at 15:26, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > > On Sat, Sep 24, 2022 at 03:10:34PM +0800, Hawkins Jiawei wrote: > > > From: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> > > > > > > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > ------------[ 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 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);
