[PATCH net] bpf: Don't redirect too small packets

[Eric Dumazet <edumazet@xxxxxxxxxx>]

Some drivers ndo_start_xmit() expect a minimal size, as shown
by various syzbot reports [1].

Willem added in commit 217e6fa24ce2 ("net: introduce device min_header_len")
the missing attribute that can be used by upper layers.

We need to use it in __bpf_redirect_common().

[1]

BUG: KMSAN: uninit-value in erspan_build_header+0x170/0x2f0 include/net/erspan.h:197
  erspan_build_header+0x170/0x2f0 include/net/erspan.h:197
  erspan_xmit+0x128a/0x1ec0 net/ipv4/ip_gre.c:706
  __netdev_start_xmit include/linux/netdevice.h:4903 [inline]
  netdev_start_xmit include/linux/netdevice.h:4917 [inline]
  xmit_one net/core/dev.c:3531 [inline]
  dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547
  sch_direct_xmit+0x3c5/0xd50 net/sched/sch_generic.c:343
  __dev_xmit_skb net/core/dev.c:3760 [inline]
  __dev_queue_xmit+0x2e6a/0x52c0 net/core/dev.c:4301
  dev_queue_xmit include/linux/netdevice.h:3091 [inline]
  __bpf_tx_skb net/core/filter.c:2136 [inline]
  __bpf_redirect_common net/core/filter.c:2180 [inline]
  __bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187
  ____bpf_clone_redirect net/core/filter.c:2460 [inline]
  bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432
  ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
  __bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238
  bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
  __bpf_prog_run include/linux/filter.h:657 [inline]
  bpf_prog_run include/linux/filter.h:664 [inline]
  bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425
  bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058
  bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4240
  __sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5649
  __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
  __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5736
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was created at:
  slab_post_alloc_hook mm/slub.c:3804 [inline]
  slab_alloc_node mm/slub.c:3845 [inline]
  kmem_cache_alloc_node+0x613/0xc50 mm/slub.c:3888
  kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577
  pskb_expand_head+0x222/0x19d0 net/core/skbuff.c:2245
  __skb_cow include/linux/skbuff.h:3671 [inline]
  skb_cow_head include/linux/skbuff.h:3705 [inline]
  erspan_xmit+0xb08/0x1ec0 net/ipv4/ip_gre.c:692
  __netdev_start_xmit include/linux/netdevice.h:4903 [inline]
  netdev_start_xmit include/linux/netdevice.h:4917 [inline]
  xmit_one net/core/dev.c:3531 [inline]
  dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547
  sch_direct_xmit+0x3c5/0xd50 net/sched/sch_generic.c:343
  __dev_xmit_skb net/core/dev.c:3760 [inline]
  __dev_queue_xmit+0x2e6a/0x52c0 net/core/dev.c:4301
  dev_queue_xmit include/linux/netdevice.h:3091 [inline]
  __bpf_tx_skb net/core/filter.c:2136 [inline]
  __bpf_redirect_common net/core/filter.c:2180 [inline]
  __bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187
  ____bpf_clone_redirect net/core/filter.c:2460 [inline]
  bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432
  ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
  __bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238
  bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
  __bpf_prog_run include/linux/filter.h:657 [inline]
  bpf_prog_run include/linux/filter.h:664 [inline]
  bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425
  bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058
  bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4240
  __sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5649
  __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
  __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5736
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

CPU: 0 PID: 5041 Comm: syz-executor167 Not tainted 6.8.0-syzkaller-11743-ga4145ce1e7bc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024

Fixes: fd1894224407 ("bpf: Don't redirect packets with invalid pkt_len")
Reported-by: syzbot+9e27778c0edc62cb97d8@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/netdev/000000000000205af206143ece22@xxxxxxxxxx/
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
---
 net/core/filter.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index 8adf95765cdd967a15b2661dfb454db0ccf350b0..745697c08acb3a74721d26ee93389efa81e973a0 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2175,6 +2175,11 @@ static int __bpf_redirect_common(struct sk_buff *skb, struct net_device *dev,
 		return -ERANGE;
 	}
 
+	if (unlikely(skb->len < dev->min_header_len)) {
+		kfree_skb(skb);
+		return -ERANGE;
+	}
+
 	bpf_push_mac_rcsum(skb);
 	return flags & BPF_F_INGRESS ?
 	       __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);
-- 
2.44.0.396.g6e790dbe36-goog