sctp: fix possible UAF in sctp_v6_available()

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

sctp: fix possible UAF in sctp_v6_available()

A lockdep report [1] with CONFIG_PROVE_RCU_LIST=y hints

that sctp_v6_available() is calling dev_get_by_index_rcu()

and ipv6_chk_addr() without holding rcu.

[1]

=============================

WARNING: suspicious RCU usage

6.12.0-rc5-virtme #1216 Tainted: G W

-----------------------------

net/core/dev.c:876 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1

1 lock held by sctp_hello/31495:

#0: ffff9f1ebbdb7418 (sk_lock-AF_INET6){+.+.}-{0:0}, at: sctp_bind (./arch/x86/include/asm/jump_label.h:27 net/sctp/socket.c:315) sctp

stack backtrace:

CPU: 7 UID: 0 PID: 31495 Comm: sctp_hello Tainted: G W 6.12.0-rc5-virtme #1216

Tainted: [W]=WARN

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

Call Trace:

<TASK>

dump_stack_lvl (lib/dump_stack.c:123)

lockdep_rcu_suspicious (kernel/locking/lockdep.c:6822)

dev_get_by_index_rcu (net/core/dev.c:876 (discriminator 7))

sctp_v6_available (net/sctp/ipv6.c:701) sctp

sctp_do_bind (net/sctp/socket.c:400 (discriminator 1)) sctp

sctp_bind (net/sctp/socket.c:320) sctp

inet6_bind_sk (net/ipv6/af_inet6.c:465)

? security_socket_bind (security/security.c:4581 (discriminator 1))

__sys_bind (net/socket.c:1848 net/socket.c:1869)

? do_user_addr_fault (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/linux/mm.h:729 arch/x86/mm/fault.c:1340)

? do_user_addr_fault (./arch/x86/include/asm/preempt.h:84 (discriminator 13) ./include/linux/rcupdate.h:98 (discriminator 13) ./include/linux/rcupdate.h:882 (discriminator 13) ./include/linux/mm.h:729 (discriminator 13) arch/x86/mm/fault.c:1340 (discriminator 13))

__x64_sys_bind (net/socket.c:1877 (discriminator 1) net/socket.c:1875 (discriminator 1) net/socket.c:1875 (discriminator 1))

do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1))

entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

RIP: 0033:0x7f59b934a1e7

Code: 44 00 00 48 8b 15 39 8c 0c 00 f7 d8 64 89 02 b8 ff ff ff ff eb bd 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 b8 31 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 09 8c 0c 00 f7 d8 64 89 01 48

All code

========

0: 44 00 00 add %r8b,(%rax)

3: 48 8b 15 39 8c 0c 00 mov 0xc8c39(%rip),%rdx # 0xc8c43

a: f7 d8 neg %eax

c: 64 89 02 mov %eax,%fs:(%rdx)

f: b8 ff ff ff ff mov $0xffffffff,%eax

14: eb bd jmp 0xffffffffffffffd3

16: 66 2e 0f 1f 84 00 00 cs nopw 0x0(%rax,%rax,1)

1d: 00 00 00

20: 0f 1f 00 nopl (%rax)

23: b8 31 00 00 00 mov $0x31,%eax

28: 0f 05 syscall

2a:* 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax <-- trapping instruction

30: 73 01 jae 0x33

32: c3 ret

33: 48 8b 0d 09 8c 0c 00 mov 0xc8c09(%rip),%rcx # 0xc8c43

3a: f7 d8 neg %eax

3c: 64 89 01 mov %eax,%fs:(%rcx)

3f: 48 rex.W

Code starting with the faulting instruction

===========================================

0: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax

6: 73 01 jae 0x9

8: c3 ret

9: 48 8b 0d 09 8c 0c 00 mov 0xc8c09(%rip),%rcx # 0xc8c19

10: f7 d8 neg %eax

12: 64 89 01 mov %eax,%fs:(%rcx)

15: 48 rex.W

RSP: 002b:00007ffe2d0ad398 EFLAGS: 00000202 ORIG_RAX: 0000000000000031

RAX: ffffffffffffffda RBX: 00007ffe2d0ad3d0 RCX: 00007f59b934a1e7

RDX: 000000000000001c RSI: 00007ffe2d0ad3d0 RDI: 0000000000000005

RBP: 0000000000000005 R08: 1999999999999999 R09: 0000000000000000

R10: 00007f59b9253298 R11: 000000000000

---truncated---