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

wifi: mac80211: fix NULL dereference at band check in starting tx ba session

In MLD connection, link_data/link_conf are dynamically allocated. They dont point to vif->bss_conf. So, there will be no chanreq assigned to vif->bss_conf and then the chan will be NULL. Tweak the code to check ht_supported/vht_supported/has_he/has_eht on sta deflink.

Crash log (with rtw89 version under MLO development): [ 9890.526087] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 9890.526102] #PF: supervisor read access in kernel mode [ 9890.526105] #PF: error_code(0x0000) - not-present page [ 9890.526109] PGD 0 P4D 0 [ 9890.526114] Oops: 0000 [#1] PREEMPT SMP PTI [ 9890.526119] CPU: 2 PID: 6367 Comm: kworker/u16:2 Kdump: loaded Tainted: G OE 6.9.0 #1 [ 9890.526123] Hardware name: LENOVO 2356AD1/2356AD1, BIOS G7ETB3WW (2.73 ) 11/28/2018 [ 9890.526126] Workqueue: phy2 rtw89_core_ba_work [rtw89_core] [ 9890.526203] RIP: 0010:ieee80211_start_tx_ba_session (net/mac80211/agg-tx.c:618 (discriminator 1)) mac80211 [ 9890.526279] Code: f7 e8 d5 93 3e ea 48 83 c4 28 89 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 49 8b 84 24 e0 f1 ff ff 48 8b 80 90 1b 00 00 <83> 38 03 0f 84 37 fe ff ff bb ea ff ff ff eb cc 49 8b 84 24 10 f3 All code

0: f7 e8 imul %eax 2: d5 (bad) 3: 93 xchg %eax,%ebx 4: 3e ea ds (bad) 6: 48 83 c4 28 add $0x28,%rsp a: 89 d8 mov %ebx,%eax c: 5b pop %rbx d: 41 5c pop %r12 f: 41 5d pop %r13 11: 41 5e pop %r14 13: 41 5f pop %r15 15: 5d pop %rbp 16: c3 retq 17: cc int3 18: cc int3 19: cc int3 1a: cc int3 1b: 49 8b 84 24 e0 f1 ff mov -0xe20(%r12),%rax 22: ff 23: 48 8b 80 90 1b 00 00 mov 0x1b90(%rax),%rax 2a:* 83 38 03 cmpl $0x3,(%rax) <– trapping instruction 2d: 0f 84 37 fe ff ff je 0xfffffffffffffe6a 33: bb ea ff ff ff mov $0xffffffea,%ebx 38: eb cc jmp 0x6 3a: 49 rex.WB 3b: 8b .byte 0x8b 3c: 84 24 10 test %ah,(%rax,%rdx,1) 3f: f3 repz

Code starting with the faulting instruction

0: 83 38 03 cmpl $0x3,(%rax) 3: 0f 84 37 fe ff ff je 0xfffffffffffffe40 9: bb ea ff ff ff mov $0xffffffea,%ebx e: eb cc jmp 0xffffffffffffffdc 10: 49 rex.WB 11: 8b .byte 0x8b 12: 84 24 10 test %ah,(%rax,%rdx,1) 15: f3 repz [ 9890.526285] RSP: 0018:ffffb8db09013d68 EFLAGS: 00010246 [ 9890.526291] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff9308e0d656c8 [ 9890.526295] RDX: 0000000000000000 RSI: ffffffffab99460b RDI: ffffffffab9a7685 [ 9890.526300] RBP: ffffb8db09013db8 R08: 0000000000000000 R09: 0000000000000873 [ 9890.526304] R10: ffff9308e0d64800 R11: 0000000000000002 R12: ffff9308e5ff6e70 [ 9890.526308] R13: ffff930952500e20 R14: ffff9309192a8c00 R15: 0000000000000000 [ 9890.526313] FS: 0000000000000000(0000) GS:ffff930b4e700000(0000) knlGS:0000000000000000 [ 9890.526316] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 9890.526318] CR2: 0000000000000000 CR3: 0000000391c58005 CR4: 00000000001706f0 [ 9890.526321] Call Trace: [ 9890.526324] [ 9890.526327] ? show_regs (arch/x86/kernel/dumpstack.c:479) [ 9890.526335] ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434) [ 9890.526340] ? page_fault_oops (arch/x86/mm/fault.c:713) [ 9890.526347] ? search_module_extables (kernel/module/main.c:3256 (discriminator —truncated—

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/021d53a3d87eeb9dbba524ac515651242a2a7e3b
• https://git.kernel.org/stable/c/0acaf4a5025d6dafb7da787d2d4c47ed95e46ed6
• https://git.kernel.org/stable/c/a53c2d847627b790fb3bd8b00e02c247941b17e0
• https://git.kernel.org/stable/c/a5594c1e03b0df3908b1e1202a1ba34422eed0f6