Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

amt: re-read skb header pointers after every pull

Several AMT receive and transmit paths cache a pointer into the skb head (ip_hdr(), ipv6_hdr(), eth_hdr() or the AMT message header) and then call a helper that can reallocate that head before the cached pointer is used again. pskb_may_pull(), ip_mc_may_pull(), ipv6_mc_may_pull(), iptunnel_pull_header(), ip_mc_check_igmp() and ipv6_mc_check_mld() can all free the old head and move the data, so a pointer taken before the call dangles afterwards and the later access is a use-after-free of the freed head.

The affected sites are:

amt_rcv() caches ip_hdr() before amt_parse_type() pulls, then reads iph->saddr.

amt_dev_xmit() caches ip_hdr()/ipv6_hdr() before ip_mc_check_igmp()/ ipv6_mc_check_mld() and pskb_may_pull(), then reads the group address.

amt_multicast_data_handler() caches eth_hdr() before pskb_may_pull(), then writes the L2 header.

amt_membership_query_handler() caches the AMT header, the outer and inner eth_hdr() and ip_hdr() before iptunnel_pull_header() and several pulls, then reads and writes them.

amt_igmpv3_report_handler() and amt_mldv2_report_handler() cache ip_hdr()/ipv6_hdr() and the current group record and read the record count from the report header inside the record loop, across the *_mc_may_pull() calls.

amt_update_handler() caches ip_hdr() and the AMT membership-update header before pskb_may_pull(),…