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Subject[PATCH 4.14 49/62] macvlan: do not assume mac_header is set in macvlan_broadcast()
Date
From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 96cc4b69581db68efc9749ef32e9cf8e0160c509 ]

Use of eth_hdr() in tx path is error prone.

Many drivers call skb_reset_mac_header() before using it,
but others do not.

Commit 6d1ccff62780 ("net: reset mac header in dev_start_xmit()")
attempted to fix this generically, but commit d346a3fae3ff
("packet: introduce PACKET_QDISC_BYPASS socket option") brought
back the macvlan bug.

Lets add a new helper, so that tx paths no longer have
to call skb_reset_mac_header() only to get a pointer
to skb->data.

Hopefully we will be able to revert 6d1ccff62780
("net: reset mac header in dev_start_xmit()") and save few cycles
in transmit fast path.

BUG: KASAN: use-after-free in __get_unaligned_cpu32 include/linux/unaligned/packed_struct.h:19 [inline]
BUG: KASAN: use-after-free in mc_hash drivers/net/macvlan.c:251 [inline]
BUG: KASAN: use-after-free in macvlan_broadcast+0x547/0x620 drivers/net/macvlan.c:277
Read of size 4 at addr ffff8880a4932401 by task syz-executor947/9579

CPU: 0 PID: 9579 Comm: syz-executor947 Not tainted 5.5.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:639
__asan_report_load_n_noabort+0xf/0x20 mm/kasan/generic_report.c:145
__get_unaligned_cpu32 include/linux/unaligned/packed_struct.h:19 [inline]
mc_hash drivers/net/macvlan.c:251 [inline]
macvlan_broadcast+0x547/0x620 drivers/net/macvlan.c:277
macvlan_queue_xmit drivers/net/macvlan.c:520 [inline]
macvlan_start_xmit+0x402/0x77f drivers/net/macvlan.c:559
__netdev_start_xmit include/linux/netdevice.h:4447 [inline]
netdev_start_xmit include/linux/netdevice.h:4461 [inline]
dev_direct_xmit+0x419/0x630 net/core/dev.c:4079
packet_direct_xmit+0x1a9/0x250 net/packet/af_packet.c:240
packet_snd net/packet/af_packet.c:2966 [inline]
packet_sendmsg+0x260d/0x6220 net/packet/af_packet.c:2991
sock_sendmsg_nosec net/socket.c:639 [inline]
sock_sendmsg+0xd7/0x130 net/socket.c:659
__sys_sendto+0x262/0x380 net/socket.c:1985
__do_sys_sendto net/socket.c:1997 [inline]
__se_sys_sendto net/socket.c:1993 [inline]
__x64_sys_sendto+0xe1/0x1a0 net/socket.c:1993
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x442639
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 5b 10 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc13549e08 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000442639
RDX: 000000000000000e RSI: 0000000020000080 RDI: 0000000000000003
RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000403bb0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9389:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
__do_kmalloc mm/slab.c:3656 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3665
kmalloc include/linux/slab.h:561 [inline]
tomoyo_realpath_from_path+0xc5/0x660 security/tomoyo/realpath.c:252
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_perm+0x230/0x430 security/tomoyo/file.c:822
tomoyo_inode_getattr+0x1d/0x30 security/tomoyo/tomoyo.c:129
security_inode_getattr+0xf2/0x150 security/security.c:1222
vfs_getattr+0x25/0x70 fs/stat.c:115
vfs_statx_fd+0x71/0xc0 fs/stat.c:145
vfs_fstat include/linux/fs.h:3265 [inline]
__do_sys_newfstat+0x9b/0x120 fs/stat.c:378
__se_sys_newfstat fs/stat.c:375 [inline]
__x64_sys_newfstat+0x54/0x80 fs/stat.c:375
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9389:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
kasan_set_free_info mm/kasan/common.c:335 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
tomoyo_realpath_from_path+0x1a7/0x660 security/tomoyo/realpath.c:289
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_perm+0x230/0x430 security/tomoyo/file.c:822
tomoyo_inode_getattr+0x1d/0x30 security/tomoyo/tomoyo.c:129
security_inode_getattr+0xf2/0x150 security/security.c:1222
vfs_getattr+0x25/0x70 fs/stat.c:115
vfs_statx_fd+0x71/0xc0 fs/stat.c:145
vfs_fstat include/linux/fs.h:3265 [inline]
__do_sys_newfstat+0x9b/0x120 fs/stat.c:378
__se_sys_newfstat fs/stat.c:375 [inline]
__x64_sys_newfstat+0x54/0x80 fs/stat.c:375
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a4932000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1025 bytes inside of
4096-byte region [ffff8880a4932000, ffff8880a4933000)
The buggy address belongs to the page:
page:ffffea0002924c80 refcount:1 mapcount:0 mapping:ffff8880aa402000 index:0x0 compound_mapcount: 0
raw: 00fffe0000010200 ffffea0002846208 ffffea00028f3888 ffff8880aa402000
raw: 0000000000000000 ffff8880a4932000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a4932300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a4932380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880a4932400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880a4932480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a4932500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Fixes: b863ceb7ddce ("[NET]: Add macvlan driver")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/macvlan.c | 2 +-
include/linux/if_ether.h | 8 ++++++++
2 files changed, 9 insertions(+), 1 deletion(-)

--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -263,7 +263,7 @@ static void macvlan_broadcast(struct sk_
struct net_device *src,
enum macvlan_mode mode)
{
- const struct ethhdr *eth = eth_hdr(skb);
+ const struct ethhdr *eth = skb_eth_hdr(skb);
const struct macvlan_dev *vlan;
struct sk_buff *nskb;
unsigned int i;
--- a/include/linux/if_ether.h
+++ b/include/linux/if_ether.h
@@ -28,6 +28,14 @@ static inline struct ethhdr *eth_hdr(con
return (struct ethhdr *)skb_mac_header(skb);
}

+/* Prefer this version in TX path, instead of
+ * skb_reset_mac_header() + eth_hdr()
+ */
+static inline struct ethhdr *skb_eth_hdr(const struct sk_buff *skb)
+{
+ return (struct ethhdr *)skb->data;
+}
+
static inline struct ethhdr *inner_eth_hdr(const struct sk_buff *skb)
{
return (struct ethhdr *)skb_inner_mac_header(skb);

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