netfilter: nf_reject: don't leak dst refcount for loopback packets

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_reject: don't leak dst refcount for loopback packets recent patches to add a WARN() when replacing skb dst entry found an old bug: WARNING: include/linux/skbuff.h:1165 skb_dst_check_unset include/linux/skbuff.h:1164 [inline] WARNING: include/linux/skbuff.h:1165 skb_dst_set include/linux/skbuff.h:1210 [inline] WARNING: include/linux/skbuff.h:1165 nf_reject_fill_skb_dst+0x2a4/0x330 net/ipv4/netfilter/nf_reject_ipv4.c:234 [..] Call Trace: nf_send_unreach+0x17b/0x6e0 net/ipv4/netfilter/nf_reject_ipv4.c:325 nft_reject_inet_eval+0x4bc/0x690 net/netfilter/nft_reject_inet.c:27 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline] .. This is because blamed commit forgot about loopback packets. Such packets already have a dst_entry attached, even at PRE_ROUTING stage. Instead of checking hook just check if the skb already has a route attached to it.

References

• https://git.kernel.org/stable/c/7b8b503c06274ef3c6c1a107743f1ec0d0a53ef8
• https://git.kernel.org/stable/c/82ef97abf22790182f7d433c74960dfd61b99c33
• https://git.kernel.org/stable/c/b7a885ba25960c91db237c3f83b4285156789bce
• https://git.kernel.org/stable/c/a0a3ace2a57887dac1e7c9a724846040c3e31868
• https://git.kernel.org/stable/c/51e8531371f90bee742c63775c9a568e5d6bf3c5
• https://git.kernel.org/stable/c/b32e1590a8d22cf7d7f965e46d5576051acf8e42
• https://git.kernel.org/stable/c/91a79b792204313153e1bdbbe5acbfc28903b3a5