ipv6: sr: fix missing sk_buff release in seg6_input_core

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

ipv6: sr: fix missing sk_buff release in seg6_input_core

The seg6_input() function is responsible for adding the SRH into a

packet, delegating the operation to the seg6_input_core(). This function

uses the skb_cow_head() to ensure that there is sufficient headroom in

the sk_buff for accommodating the link-layer header.

In the event that the skb_cow_header() function fails, the

seg6_input_core() catches the error but it does not release the sk_buff,

which will result in a memory leak.

This issue was introduced in commit af3b5158b89d ("ipv6: sr: fix BUG due

to headroom too small after SRH push") and persists even after commit

7a3f5b0de364 ("netfilter: add netfilter hooks to SRv6 data plane"),

where the entire seg6_input() code was refactored to deal with netfilter

hooks.

The proposed patch addresses the identified memory leak by requiring the

seg6_input_core() function to release the sk_buff in the event that

skb_cow_head() fails.