Subject: CVE-2024-26657: drm/sched: fix null-ptr-deref in init entity

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

drm/sched: fix null-ptr-deref in init entity

The bug can be triggered by sending an amdgpu_cs_wait_ioctl
to the AMDGPU DRM driver on any ASICs with valid context.
The bug was reported by Joonkyo Jung <[email-masked]>.
For example the following code:

    static void Syzkaller2(int fd)
    {
	union drm_amdgpu_ctx arg1;
	union drm_amdgpu_wait_cs arg2;

	arg1.in.op = AMDGPU_CTX_OP_ALLOC_CTX;
	ret = drmIoctl(fd, 0x140106442 /* amdgpu_ctx_ioctl */, &arg1);

	arg2.in.handle = 0x0;
	arg2.in.timeout = 0x2000000000000;
	arg2.in.ip_type = AMD_IP_VPE /* 0x9 */;
	arg2->in.ip_instance = 0x0;
	arg2.in.ring = 0x0;
	arg2.in.ctx_id = arg1.out.alloc.ctx_id;

	drmIoctl(fd, 0xc0206449 /* AMDGPU_WAIT_CS * /, &arg2);
    }

The ioctl AMDGPU_WAIT_CS without previously submitted job could be assumed that
the error should be returned, but the following commit 1decbf6bb0b4dc56c9da6c5e57b994ebfc2be3aa
modified the logic and allowed to have sched_rq equal to NULL.

As a result when there is no job the ioctl AMDGPU_WAIT_CS returns success.
The change fixes null-ptr-deref in init entity and the stack below demonstrates
the error condition:

[  +0.000007] BUG: kernel NULL pointer dereference, address: 0000000000000028
[  +0.007086] #PF: supervisor read access in kernel mode
[  +0.005234] #PF: error_code(0x0000) - not-present page
[  +0.005232] PGD 0 P4D 0
[  +0.002501] Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
[  +0.005034] CPU: 10 PID: 9229 Comm: amd_basic Tainted: G    B   W    L     6.7.0+ #4
[  +0.007797] Hardware name: ASUS System Product Name/ROG STRIX B550-F GAMING (WI-FI), BIOS 1401 12/03/2020
[  +0.009798] RIP: 0010:drm_sched_entity_init+0x2d3/0x420 [gpu_sched]
[  +0.006426] Code: 80 00 00 00 00 00 00 00 e8 1a 81 82 e0 49 89 9c 24 c0 00 00 00 4c 89 ef e8 4a 80 82 e0 49 8b 5d 00 48 8d 7b 28 e8 3d 80 82 e0 <48> 83 7b 28 00 0f 84 28 01 00 00 4d 8d ac 24 98 00 00 00 49 8d 5c
[  +0.019094] RSP: 0018:ffffc90014c1fa40 EFLAGS: 00010282
[  +0.005237] RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff8113f3fa
[  +0.007326] RDX: fffffbfff0a7889d RSI: 0000000000000008 RDI: ffffffff853c44e0
[  +0.007264] RBP: ffffc90014c1fa80 R08: 0000000000000001 R09: fffffbfff0a7889c
[  +0.007266] R10: ffffffff853c44e7 R11: 0000000000000001 R12: ffff8881a719b010
[  +0.007263] R13: ffff88810d412748 R14: 0000000000000002 R15: 0000000000000000
[  +0.007264] FS:  00007ffff7045540(0000) GS:ffff8883cc900000(0000) knlGS:0000000000000000
[  +0.008236] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  +0.005851] CR2: 0000000000000028 CR3: 000000011912e000 CR4: 0000000000350ef0
[  +0.007175] Call Trace:
[  +0.002561]  <TASK>
[  +0.002141]  ? show_regs+0x6a/0x80
[  +0.003473]  ? __die+0x25/0x70
[  +0.003124]  ? page_fault_oops+0x214/0x720
[  +0.004179]  ? preempt_count_sub+0x18/0xc0
[  +0.004093]  ? __pfx_page_fault_oops+0x10/0x10
[  +0.004590]  ? srso_return_thunk+0x5/0x5f
[  +0.004000]  ? vprintk_default+0x1d/0x30
[  +0.004063]  ? srso_return_thunk+0x5/0x5f
[  +0.004087]  ? vprintk+0x5c/0x90
[  +0.003296]  ? drm_sched_entity_init+0x2d3/0x420 [gpu_sched]
[  +0.005807]  ? srso_return_thunk+0x5/0x5f
[  +0.004090]  ? _printk+0xb3/0xe0
[  +0.003293]  ? __pfx__printk+0x10/0x10
[  +0.003735]  ? asm_sysvec_apic_timer_interrupt+0x1b/0x20
[  +0.005482]  ? do_user_addr_fault+0x345/0x770
[  +0.004361]  ? exc_page_fault+0x64/0xf0
[  +0.003972]  ? asm_exc_page_fault+0x27/0x30
[  +0.004271]  ? add_taint+0x2a/0xa0
[  +0.003476]  ? drm_sched_entity_init+0x2d3/0x420 [gpu_sched]
[  +0.005812]  amdgpu_ctx_get_entity+0x3f9/0x770 [amdgpu]
[  +0.009530]  ? finish_task_switch.isra.0+0x129/0x470
[  +0.005068]  ? __pfx_amdgpu_ctx_get_entity+0x10/0x10 [amdgpu]
[  +0.010063]  ? __kasan_check_write+0x14/0x20
[  +0.004356]  ? srso_return_thunk+0x5/0x5f
[  +0.004001]  ? mutex_unlock+0x81/0xd0
[  +0.003802]  ? srso_return_thunk+0x5/0x5f
[  +0.004096]  amdgpu_cs_wait_ioctl+0xf6/0x270 [amdgpu]
[  +0.009355]  ? __pfx_amdgpu_cs_wait_ioctl+0x10/0x10 [amdgpu]
[  +0.009981]  ? srso_return_thunk+0x5/0x5f
[  +0.004089]  ? srso_return_thunk+0x5/0x5f
[  +0.004090]  ? __srcu_read_lock+0x20/0x50
[  +0.004096]  drm_ioctl_kernel+0x140/0x1f0 [drm]
[  +0.005080]  ? __pfx_amdgpu_cs_wait_ioctl+0x10/0x10 [amdgpu]
[  +0.009974]  ? __pfx_drm_ioctl_kernel+0x10/0x10 [drm]
[  +0.005618]  ? srso_return_thunk+0x5/0x5f
[  +0.004088]  ? __kasan_check_write+0x14/0x20
[  +0.004357]  drm_ioctl+0x3da/0x730 [drm]
[  +0.004461]  ? __pfx_amdgpu_cs_wait_ioctl+0x10/0x10 [amdgpu]
[  +0.009979]  ? __pfx_drm_ioctl+0x10/0x10 [drm]
[  +0.004993]  ? srso_return_thunk+0x5/0x5f
[  +0.004090]  ? __kasan_check_write+0x14/0x20
[  +0.004356]  ? srso_return_thunk+0x5/0x5f
[  +0.004090]  ? _raw_spin_lock_irqsave+0x99/0x100
[  +0.004712]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[  +0.005063]  ? __pfx_arch_do_signal_or_restart+0x10/0x10
[  +0.005477]  ? srso_return_thunk+0x5/0x5f
[  +0.004000]  ? preempt_count_sub+0x18/0xc0
[  +0.004237]  ? srso_return_thunk+0x5/0x5f
[  +0.004090]  ? _raw_spin_unlock_irqrestore+0x27/0x50
[  +0.005069]  amdgpu_drm_ioctl+0x7e/0xe0 [amdgpu]
[  +0.008912]  __x64_sys_ioctl+0xcd/0x110
[  +0.003918]  do_syscall_64+0x5f/0xe0
[  +0.003649]  ? noist_exc_debug+0xe6/0x120
[  +0.004095]  entry_SYSCALL_64_after_hwframe+0x6e/0x76
[  +0.005150] RIP: 0033:0x7ffff7b1a94f
[  +0.003647] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 77 1f 48 8b 44 24 18 64 48 2b 04 25 28 00
[  +0.019097] RSP: 002b:00007fffffffe0a0 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  +0.007708] RAX: ffffffffffffffda RBX: 000055555558b360 RCX: 00007ffff7b1a94f
[  +0.007176] RDX: 000055555558b360 RSI: 00000000c0206449 RDI: 0000000000000003
[  +0.007326] RBP: 00000000c0206449 R08: 000055555556ded0 R09: 000000007fffffff
[  +0.007176] R10: 0000000000000000 R11: 0000000000000246 R12: 00007fffffffe5d8
[  +0.007238] R13: 0000000000000003 R14: 000055555555cba8 R15: 00007ffff7ffd040
[  +0.007250]  </TASK>

v2: Reworked check to guard against null ptr deref and added helpful comments
    (Christian)

The Linux kernel CVE team has assigned CVE-2024-26657 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.7 with commit 56e449603f0a and fixed in 6.7.12 with commit 74cd204c7afe
	Issue introduced in 6.7 with commit 56e449603f0a and fixed in 6.8.3 with commit 54b5b7275dfd
	Issue introduced in 6.7 with commit 56e449603f0a and fixed in 6.9 with commit f34e8bb7d6c6

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-26657
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/scheduler/sched_entity.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/74cd204c7afe498aa9dcc3ebf0ecac53d477a429
	https://git.kernel.org/stable/c/54b5b7275dfdec35812ccce70930cd7c4ee612b2
	https://git.kernel.org/stable/c/f34e8bb7d6c6626933fe993e03ed59ae85e16abb