net: tls: explicitly disallow disconnect

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: tls: explicitly disallow disconnect syzbot discovered that it can disconnect a TLS socket and then run into all sort of unexpected corner cases. I have a vague recollection of Eric pointing this out to us a long time ago. Supporting disconnect is really hard, for one thing if offload is enabled we'd need to wait for all packets to be _acked_. Disconnect is not commonly used, disallow it. The immediate problem syzbot run into is the warning in the strp, but that's just the easiest bug to trigger: WARNING: CPU: 0 PID: 5834 at net/tls/tls_strp.c:486 tls_strp_msg_load+0x72e/0xa80 net/tls/tls_strp.c:486 RIP: 0010:tls_strp_msg_load+0x72e/0xa80 net/tls/tls_strp.c:486 Call Trace: <TASK> tls_rx_rec_wait+0x280/0xa60 net/tls/tls_sw.c:1363 tls_sw_recvmsg+0x85c/0x1c30 net/tls/tls_sw.c:2043 inet6_recvmsg+0x2c9/0x730 net/ipv6/af_inet6.c:678 sock_recvmsg_nosec net/socket.c:1023 [inline] sock_recvmsg+0x109/0x280 net/socket.c:1045 __sys_recvfrom+0x202/0x380 net/socket.c:2237

References

• https://git.kernel.org/stable/c/7bdcf5bc35ae59fc4a0fa23276e84b4d1534a3cf
• https://git.kernel.org/stable/c/ac91c6125468be720eafde9c973994cb45b61d44
• https://git.kernel.org/stable/c/f3ce4d3f874ab7919edca364c147ac735f9f1d04
• https://git.kernel.org/stable/c/2bcad8fefcecdd5f005d8c550b25d703c063c34a
• https://git.kernel.org/stable/c/9fcbca0f801580cbb583e9cb274e2c7fbe766ca6
• https://git.kernel.org/stable/c/c665bef891e8972e1d3ce5bbc0d42a373346a2c3
• https://git.kernel.org/stable/c/8513411ec321942bd3cfed53d5bb700665c67d86
• https://git.kernel.org/stable/c/5071a1e606b30c0c11278d3c6620cd6a24724cf6