xfrm: espintcp: fix UAF during close

Overview

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

xfrm: espintcp: fix UAF during close

ZDI reported and analyzed a race condition during close for espintcp sockets:

espintcp_close() frees emsg->skb via kfree_skb() without holding
any socket lock. Concurrently, the xfrm_trans_reinject work queue
invokes esp_output_tcp_finish() -> espintcp_push_skb() ->
espintcp_push_msgs() -> skb_send_sock_locked(), which reads the
same skb as a data source.

Fix this by adding a synchronize_rcu() call after resetting sk_prot, since esp_output_tcp_finish() runs under RCU and won't use a socket with sk_prot == &tcp_prot. Simply taking the socket lock in espintcp_close() could lead to leaks, if esp_output_tcp_finish() re-adds an skb in the slot we just freed. After this, the existing barrier() is no longer needed.

Affected

• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 29121c5e6591da527e8e36ddac7120dc527f574d
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < ed5d9102190c45fc70121c036b0626b740040b75
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 4bc0dfa28dca6fc0084203732695968049c44072
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < ff8dd7a932f34409a56e1b91a1219340f17457e9
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 4b31a875693c480c611519faca46216514e3e052
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 24efebecf415ba264adba0f0491cec436463a14f
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < eb3bbf29c723fe75c0eb92be14f0ec92971fe272
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 54b41ad14da9a981131ab6e4d3f79321a503ea5d
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < deb232e884877bf10b4ce2580909eedec986c284
• Linux 5.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.