In the Linux kernel, the following vulnerability has been resolved:
bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets
With a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages
sent from one TCP socket (s1) to actually egress from another TCP
socket (s2):
tcp_bpf_sendmsg(s1) // = sk_prot->sendmsg
tcp_bpf_send_verdict(s1) // __SK_REDIRECT case
tcp_bpf_sendmsg_redir(s2)
tcp_bpf_push_locked(s2)
tcp_bpf_push(s2)
tcp_rate_check_app_limited(s2) // expects tcp_sock
tcp_sendmsg_locked(s2) // ditto
There is a hard-coded assumption in the call-chain, that the egress
socket (s2) is a TCP socket.
However in commit 122e6c79efe1 (“sock_map: Update sock type checks for
UDP”) we have enabled redirects to non-TCP sockets. This was done for the
sake of BPF sk_skb programs. There was no indention to support sk_msg
send-to-egress use case.
As a result, attempts to send-to-egress through a non-TCP socket lead to a
crash due to invalid downcast from sock to tcp_sock:
BUG: kernel NULL pointer dereference, address: 000000000000002f
…
Call Trace:
<TASK>
? show_regs+0x60/0x70
? __die+0x1f/0x70
? page_fault_oops+0x80/0x160
? do_user_addr_fault+0x2d7/0x800
? rcu_is_watching+0x11/0x50
? exc_page_fault+0x70/0x1c0
? asm_exc_page_fault+0x27/0x30
? tcp_tso_segs+0x14/0xa0
tcp_write_xmit+0x67/0xce0
__tcp_push_pending_frames+0x32/0xf0
tcp_push+0x107/0x140
tcp_sendmsg_locked+0x99f/0xbb0
tcp_bpf_push+0x19d/0x3a0
tcp_bpf_sendmsg_redir+0x55/0xd0
tcp_bpf_send_verdict+0x407/0x550
tcp_bpf_sendmsg+0x1a1/0x390
inet_sendmsg+0x6a/0x70
sock_sendmsg+0x9d/0xc0
? sockfd_lookup_light+0x12/0x80
__sys_sendto+0x10e/0x160
? syscall_enter_from_user_mode+0x20/0x60
? __this_cpu_preempt_check+0x13/0x20
? lockdep_hardirqs_on+0x82/0x110
__x64_sys_sendto+0x1f/0x30
do_syscall_64+0x38/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Reject selecting a non-TCP sockets as redirect target from a BPF sk_msg
program to prevent the crash. When attempted, user will receive an EACCES
error from send/sendto/sendmsg() syscall.
[
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"net/core/sock_map.c"
],
"versions": [
{
"version": "122e6c79efe1",
"lessThan": "bc8b89b69638",
"status": "affected",
"versionType": "git"
},
{
"version": "122e6c79efe1",
"lessThan": "b8f97e47b6fb",
"status": "affected",
"versionType": "git"
},
{
"version": "122e6c79efe1",
"lessThan": "ded6e448028f",
"status": "affected",
"versionType": "git"
},
{
"version": "122e6c79efe1",
"lessThan": "b80e31baa436",
"status": "affected",
"versionType": "git"
}
]
},
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "affected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"net/core/sock_map.c"
],
"versions": [
{
"version": "5.13",
"status": "affected"
},
{
"version": "0",
"lessThan": "5.13",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.15.135",
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "6.1.57",
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "6.5.7",
"lessThanOrEqual": "6.5.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "6.6",
"lessThanOrEqual": "*",
"status": "unaffected",
"versionType": "original_commit_for_fix"
}
]
}
]