| Message ID | 20230720004410.87588-3-kuniyu@amazon.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: Fix error/warning by -fstrict-flex-arrays=3 | expand |
Kuniyuki Iwashima wrote: > syzkaller found a warning in packet_getname() [0], where we try to > copy 16 bytes to sockaddr_ll.sll_addr[8]. > > Some devices (ip6gre, vti6, ip6tnl) have 16 bytes address expressed > by struct in6_addr. Also, Infiniband has 32 bytes as MAX_ADDR_LEN. > > The write seems to overflow, but actually not since we use struct > sockaddr_storage defined in __sys_getsockname() and its size is 128 > (_K_SS_MAXSIZE) bytes. Thus, we have sufficient room after sll_addr[] > as __data[]. > > To avoid the warning, we need to let __fortify_memcpy_chk() know the > actual buffer size. > > Another option would be to use strncpy() and limit the copied length > to sizeof(sll_addr), but it will return the partial address and break > an application that passes sockaddr_storage to getsockname(). > > [0]: > memcpy: detected field-spanning write (size 16) of single field "sll->sll_addr" at net/packet/af_packet.c:3604 (size 8) > WARNING: CPU: 0 PID: 255 at net/packet/af_packet.c:3604 packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 > Modules linked in: > CPU: 0 PID: 255 Comm: syz-executor750 Not tainted 6.5.0-rc1-00330-g60cc1f7d0605 #4 > Hardware name: linux,dummy-virt (DT) > pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > pc : packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 > lr : packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 > sp : ffff800089887bc0 > x29: ffff800089887bc0 x28: ffff000010f80f80 x27: 0000000000000003 > x26: dfff800000000000 x25: ffff700011310f80 x24: ffff800087d55000 > x23: dfff800000000000 x22: ffff800089887c2c x21: 0000000000000010 > x20: ffff00000de08310 x19: ffff800089887c20 x18: ffff800086ab1630 > x17: 20646c6569662065 x16: 6c676e697320666f x15: 0000000000000001 > x14: 1fffe0000d56d7ca x13: 0000000000000000 x12: 0000000000000000 > x11: 0000000000000000 x10: 0000000000000000 x9 : 3e60944c3da92b00 > x8 : 3e60944c3da92b00 x7 : 0000000000000001 x6 : 0000000000000001 > x5 : ffff8000898874f8 x4 : ffff800086ac99e0 x3 : ffff8000803f8808 > x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000000 > Call trace: > packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 > __sys_getsockname+0x168/0x24c net/socket.c:2042 > __do_sys_getsockname net/socket.c:2057 [inline] > __se_sys_getsockname net/socket.c:2054 [inline] > __arm64_sys_getsockname+0x7c/0x94 net/socket.c:2054 > __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] > invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52 > el0_svc_common+0x134/0x240 arch/arm64/kernel/syscall.c:139 > do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:188 > el0_svc+0x2c/0x7c arch/arm64/kernel/entry-common.c:647 > el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:665 > el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591 > > Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3") > Reported-by: syzkaller <syzkaller@googlegroups.com> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Reviewed-by: Willem de Bruijn <willemb@google.com>
On Wed, Jul 19, 2023 at 05:44:10PM -0700, Kuniyuki Iwashima wrote: > syzkaller found a warning in packet_getname() [0], where we try to > copy 16 bytes to sockaddr_ll.sll_addr[8]. > > Some devices (ip6gre, vti6, ip6tnl) have 16 bytes address expressed > by struct in6_addr. Also, Infiniband has 32 bytes as MAX_ADDR_LEN. > > The write seems to overflow, but actually not since we use struct > sockaddr_storage defined in __sys_getsockname() and its size is 128 > (_K_SS_MAXSIZE) bytes. Thus, we have sufficient room after sll_addr[] > as __data[]. Ah, so the issue here is that the UAPI for sll_addr is lying about its size. I think a better fix here is to fix the structure (without breaking UAPI sizes or names): diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h index 9efc42382fdb..4d0ad22f83b5 100644 --- a/include/uapi/linux/if_packet.h +++ b/include/uapi/linux/if_packet.h @@ -18,7 +18,11 @@ struct sockaddr_ll { unsigned short sll_hatype; unsigned char sll_pkttype; unsigned char sll_halen; - unsigned char sll_addr[8]; + union { + unsigned char sll_addr[8]; + /* Actual length is in sll_halen. */ + __DECLARE_FLEX_ARRAY(unsigned char, sll_addr_flex); + }; }; /* Packet types */ diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 85ff90a03b0c..8e3ddec4c3d5 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -3601,7 +3601,7 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr, if (dev) { sll->sll_hatype = dev->type; sll->sll_halen = dev->addr_len; - memcpy(sll->sll_addr, dev->dev_addr, dev->addr_len); + memcpy(sll->sll_addr_flex, dev->dev_addr, dev->addr_len); } else { sll->sll_hatype = 0; /* Bad: we have no ARPHRD_UNSPEC */ sll->sll_halen = 0; We can't rename sll_data nor change it's size, as userspace uses it pretty extensively: https://codesearch.debian.net/search?q=sizeof.*sll_addr&literal=0
From: Kees Cook <keescook@chromium.org> Date: Thu, 20 Jul 2023 08:04:53 -0700 > On Wed, Jul 19, 2023 at 05:44:10PM -0700, Kuniyuki Iwashima wrote: > > syzkaller found a warning in packet_getname() [0], where we try to > > copy 16 bytes to sockaddr_ll.sll_addr[8]. > > > > Some devices (ip6gre, vti6, ip6tnl) have 16 bytes address expressed > > by struct in6_addr. Also, Infiniband has 32 bytes as MAX_ADDR_LEN. > > > > The write seems to overflow, but actually not since we use struct > > sockaddr_storage defined in __sys_getsockname() and its size is 128 > > (_K_SS_MAXSIZE) bytes. Thus, we have sufficient room after sll_addr[] > > as __data[]. > > Ah, so the issue here is that the UAPI for sll_addr is lying about its > size. I think a better fix here is to fix the structure (without > breaking UAPI sizes or names): Doesn't it forcify sll_addr here ? > > diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h > index 9efc42382fdb..4d0ad22f83b5 100644 > --- a/include/uapi/linux/if_packet.h > +++ b/include/uapi/linux/if_packet.h > @@ -18,7 +18,11 @@ struct sockaddr_ll { > unsigned short sll_hatype; > unsigned char sll_pkttype; > unsigned char sll_halen; > - unsigned char sll_addr[8]; > + union { > + unsigned char sll_addr[8]; > + /* Actual length is in sll_halen. */ > + __DECLARE_FLEX_ARRAY(unsigned char, sll_addr_flex); > + }; > }; > > /* Packet types */ > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 85ff90a03b0c..8e3ddec4c3d5 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -3601,7 +3601,7 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr, > if (dev) { > sll->sll_hatype = dev->type; > sll->sll_halen = dev->addr_len; > - memcpy(sll->sll_addr, dev->dev_addr, dev->addr_len); > + memcpy(sll->sll_addr_flex, dev->dev_addr, dev->addr_len); > } else { > sll->sll_hatype = 0; /* Bad: we have no ARPHRD_UNSPEC */ > sll->sll_halen = 0; > > We can't rename sll_data nor change it's size, as userspace uses it > pretty extensively: > https://codesearch.debian.net/search?q=sizeof.*sll_addr&literal=0 > > -- > Kees Cook
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 85ff90a03b0c..7f60b78f170f 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -3601,7 +3601,12 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr, if (dev) { sll->sll_hatype = dev->type; sll->sll_halen = dev->addr_len; - memcpy(sll->sll_addr, dev->dev_addr, dev->addr_len); + + /* Let __fortify_memcpy_chk() know the actual buffer size. */ + memcpy(((struct sockaddr_storage *)sll)->__data + + offsetof(struct sockaddr_ll, sll_addr) - + offsetof(struct sockaddr_ll, sll_protocol), + dev->dev_addr, dev->addr_len); } else { sll->sll_hatype = 0; /* Bad: we have no ARPHRD_UNSPEC */ sll->sll_halen = 0;
syzkaller found a warning in packet_getname() [0], where we try to copy 16 bytes to sockaddr_ll.sll_addr[8]. Some devices (ip6gre, vti6, ip6tnl) have 16 bytes address expressed by struct in6_addr. Also, Infiniband has 32 bytes as MAX_ADDR_LEN. The write seems to overflow, but actually not since we use struct sockaddr_storage defined in __sys_getsockname() and its size is 128 (_K_SS_MAXSIZE) bytes. Thus, we have sufficient room after sll_addr[] as __data[]. To avoid the warning, we need to let __fortify_memcpy_chk() know the actual buffer size. Another option would be to use strncpy() and limit the copied length to sizeof(sll_addr), but it will return the partial address and break an application that passes sockaddr_storage to getsockname(). [0]: memcpy: detected field-spanning write (size 16) of single field "sll->sll_addr" at net/packet/af_packet.c:3604 (size 8) WARNING: CPU: 0 PID: 255 at net/packet/af_packet.c:3604 packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 Modules linked in: CPU: 0 PID: 255 Comm: syz-executor750 Not tainted 6.5.0-rc1-00330-g60cc1f7d0605 #4 Hardware name: linux,dummy-virt (DT) pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 lr : packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 sp : ffff800089887bc0 x29: ffff800089887bc0 x28: ffff000010f80f80 x27: 0000000000000003 x26: dfff800000000000 x25: ffff700011310f80 x24: ffff800087d55000 x23: dfff800000000000 x22: ffff800089887c2c x21: 0000000000000010 x20: ffff00000de08310 x19: ffff800089887c20 x18: ffff800086ab1630 x17: 20646c6569662065 x16: 6c676e697320666f x15: 0000000000000001 x14: 1fffe0000d56d7ca x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 3e60944c3da92b00 x8 : 3e60944c3da92b00 x7 : 0000000000000001 x6 : 0000000000000001 x5 : ffff8000898874f8 x4 : ffff800086ac99e0 x3 : ffff8000803f8808 x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000000 Call trace: packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604 __sys_getsockname+0x168/0x24c net/socket.c:2042 __do_sys_getsockname net/socket.c:2057 [inline] __se_sys_getsockname net/socket.c:2054 [inline] __arm64_sys_getsockname+0x7c/0x94 net/socket.c:2054 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x134/0x240 arch/arm64/kernel/syscall.c:139 do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:188 el0_svc+0x2c/0x7c arch/arm64/kernel/entry-common.c:647 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:665 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591 Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3") Reported-by: syzkaller <syzkaller@googlegroups.com> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> --- net/packet/af_packet.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)