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net/sched: act_ct: fix wild memory access when clearing fragments 

while testing re-assembly/re-fragmentation using act_ct, it's possible to
observe a crash like the following one:

 KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f]
 CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S                5.12.0-rc7+ #424
 Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017
 RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0
 Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48
 RSP: 0018:ffff888c31449db8 EFLAGS: 00010203
 RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960
 RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e
 RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350
 R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000
 R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160
 FS:  0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  <IRQ>
  inet_frag_destroy+0xa9/0x150
  call_timer_fn+0x2d/0x180
  run_timer_softirq+0x4fe/0xe70
  __do_softirq+0x197/0x5a0
  irq_exit_rcu+0x1de/0x200
  sysvec_apic_timer_interrupt+0x6b/0x80
  </IRQ>

when act_ct temporarily stores an IP fragment, restoring the skb qdisc cb
results in putting random data in FRAG_CB(), and this causes those "wild"
memory accesses later, when the rbtree is purged. Never overwrite the skb
cb in case tcf_ct_handle_fragments() returns -EINPROGRESS.

Fixes: ae372cb175 ("net/sched: act_ct: fix restore the qdisc_skb_cb after defrag")
Fixes: 7baf2429a1 ("net/sched: cls_flower add CT_FLAGS_INVALID flag support")
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Davide Caratti 2021-04-26 17:45:51 +02:00 committed by David S. Miller
parent 63fa73e215
commit f77bd544a6
1 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
net/sched/act_ct.c
View File

@ -732,7 +732,8 @@ static int tcf_ct_handle_fragments(struct net *net, struct sk_buff *skb,
#endif
}
*qdisc_skb_cb(skb) = cb;
if (err != -EINPROGRESS)
*qdisc_skb_cb(skb) = cb;
skb_clear_hash(skb);
skb->ignore_df = 1;
return err;
@ -967,7 +968,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
err = tcf_ct_handle_fragments(net, skb, family, p->zone, &defrag);
if (err == -EINPROGRESS) {
retval = TC_ACT_STOLEN;
goto out;
goto out_clear;
}
if (err)
goto drop;
@ -1030,7 +1031,6 @@ do_nat:
out_push:
skb_push_rcsum(skb, nh_ofs);
out:
qdisc_skb_cb(skb)->post_ct = true;
out_clear:
tcf_action_update_bstats(&c->common, skb);