Re: [PATCH] drm/amd/display: Fix NULL deref in debugfs odm_combine_segments

[Rong Zhang <i@rong.moe>]

Hi all,

On Tue, 2025-10-14 at 00:47 +0800, Rong Zhang wrote:
> When a connector is connected but inactive (e.g., disabled by desktop
> environments), pipe_ctx->stream_res.tg will be destroyed. Then, reading
> odm_combine_segments causes kernel NULL pointer dereference.
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000000
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: Oops: 0000 [#1] SMP NOPTI
>  CPU: 16 UID: 0 PID: 26474 Comm: cat Not tainted 6.17.0+ #2 PREEMPT(lazy)  e6a17af9ee6db7c63e9d90dbe5b28ccab67520c6
>  Hardware name: LENOVO 21Q4/LNVNB161216, BIOS PXCN25WW 03/27/2025
>  RIP: 0010:odm_combine_segments_show+0x93/0xf0 [amdgpu]
>  Code: 41 83 b8 b0 00 00 00 01 75 6e 48 98 ba a1 ff ff ff 48 c1 e0 0c 48 8d 8c 07 d8 02 00 00 48 85 c9 74 2d 48 8b bc 07 f0 08 00 00 <48> 8b 07 48 8b 80 08 02 00>
>  RSP: 0018:ffffd1bf4b953c58 EFLAGS: 00010286
>  RAX: 0000000000005000 RBX: ffff8e35976b02d0 RCX: ffff8e3aeed052d8
>  RDX: 00000000ffffffa1 RSI: ffff8e35a3120800 RDI: 0000000000000000
>  RBP: 0000000000000000 R08: ffff8e3580eb0000 R09: ffff8e35976b02d0
>  R10: ffffd1bf4b953c78 R11: 0000000000000000 R12: ffffd1bf4b953d08
>  R13: 0000000000040000 R14: 0000000000000001 R15: 0000000000000001
>  FS:  00007f44d3f9f740(0000) GS:ffff8e3caa47f000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000000 CR3: 00000006485c2000 CR4: 0000000000f50ef0
>  PKRU: 55555554
>  Call Trace:
>   <TASK>
>   seq_read_iter+0x125/0x490
>   ? __alloc_frozen_pages_noprof+0x18f/0x350
>   seq_read+0x12c/0x170
>   full_proxy_read+0x51/0x80
>   vfs_read+0xbc/0x390
>   ? __handle_mm_fault+0xa46/0xef0
>   ? do_syscall_64+0x71/0x900
>   ksys_read+0x73/0xf0
>   do_syscall_64+0x71/0x900
>   ? count_memcg_events+0xc2/0x190
>   ? handle_mm_fault+0x1d7/0x2d0
>   ? do_user_addr_fault+0x21a/0x690
>   ? exc_page_fault+0x7e/0x1a0
>   entry_SYSCALL_64_after_hwframe+0x6c/0x74
>  RIP: 0033:0x7f44d4031687
>  Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00>
>  RSP: 002b:00007ffdb4b5f0b0 EFLAGS: 00000202 ORIG_RAX: 0000000000000000
>  RAX: ffffffffffffffda RBX: 00007f44d3f9f740 RCX: 00007f44d4031687
>  RDX: 0000000000040000 RSI: 00007f44d3f5e000 RDI: 0000000000000003
>  RBP: 0000000000040000 R08: 0000000000000000 R09: 0000000000000000
>  R10: 0000000000000000 R11: 0000000000000202 R12: 00007f44d3f5e000
>  R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000040000
>   </TASK>
>  Modules linked in: tls tcp_diag inet_diag xt_mark ccm snd_hrtimer snd_seq_dummy snd_seq_midi snd_seq_oss snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device x>
>   snd_hda_codec_atihdmi snd_hda_codec_realtek_lib lenovo_wmi_helpers think_lmi snd_hda_codec_generic snd_hda_codec_hdmi snd_soc_core kvm snd_compress uvcvideo sn>
>   platform_profile joydev amd_pmc mousedev mac_hid sch_fq_codel uinput i2c_dev parport_pc ppdev lp parport nvme_fabrics loop nfnetlink ip_tables x_tables dm_cryp>
>  CR2: 0000000000000000
>  ---[ end trace 0000000000000000 ]---
>  RIP: 0010:odm_combine_segments_show+0x93/0xf0 [amdgpu]
>  Code: 41 83 b8 b0 00 00 00 01 75 6e 48 98 ba a1 ff ff ff 48 c1 e0 0c 48 8d 8c 07 d8 02 00 00 48 85 c9 74 2d 48 8b bc 07 f0 08 00 00 <48> 8b 07 48 8b 80 08 02 00>
>  RSP: 0018:ffffd1bf4b953c58 EFLAGS: 00010286
>  RAX: 0000000000005000 RBX: ffff8e35976b02d0 RCX: ffff8e3aeed052d8
>  RDX: 00000000ffffffa1 RSI: ffff8e35a3120800 RDI: 0000000000000000
>  RBP: 0000000000000000 R08: ffff8e3580eb0000 R09: ffff8e35976b02d0
>  R10: ffffd1bf4b953c78 R11: 0000000000000000 R12: ffffd1bf4b953d08
>  R13: 0000000000040000 R14: 0000000000000001 R15: 0000000000000001
>  FS:  00007f44d3f9f740(0000) GS:ffff8e3caa47f000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000000 CR3: 00000006485c2000 CR4: 0000000000f50ef0
>  PKRU: 55555554
> 
> Fix this by checking pipe_ctx->stream_res.tg before dereferencing.
> 
> Fixes: 07926ba8a44f ("drm/amd/display: Add debugfs interface for ODM combine info")
> Cc: stable@vger.kernel.org
> Signed-off-by: Rong Zhang <i@rong.moe>
> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c
> index f263e1a4537e1..00dac862b665a 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c
> @@ -1302,7 +1302,8 @@ static int odm_combine_segments_show(struct seq_file *m, void *unused)
>  	if (connector->status != connector_status_connected)
>  		return -ENODEV;
>  
> -	if (pipe_ctx != NULL && pipe_ctx->stream_res.tg->funcs->get_odm_combine_segments)
> +	if (pipe_ctx && pipe_ctx->stream_res.tg &&
> +	    pipe_ctx->stream_res.tg->funcs->get_odm_combine_segments)
>  		pipe_ctx->stream_res.tg->funcs->get_odm_combine_segments(pipe_ctx->stream_res.tg, &segments);
>  
>  	seq_printf(m, "%d\n", segments);
> 
> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787

Gentle ping.

Thanks,
Rong