CVE-2024-26728: drm/amd/display: fix null-pointer dereference on edid reading
In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: fix null-pointer dereference on edid reading

Use i2c adapter when there isn't aux_mode in dc_link to fix a
null-pointer derefence that happens when running
igt@kms_force_connector_basic in a system with DCN2.1 and HDMI connector
detected as below:

[  +0.178146] BUG: kernel NULL pointer dereference, address: 00000000000004c0
[  +0.000010] #PF: supervisor read access in kernel mode
[  +0.000005] #PF: error_code(0x0000) - not-present page
[  +0.000004] PGD 0 P4D 0
[  +0.000006] Oops: 0000 [#1] PREEMPT SMP NOPTI
[  +0.000006] CPU: 15 PID: 2368 Comm: kms_force_conne Not tainted 6.5.0-asdn+ #152
[  +0.000005] Hardware name: HP HP ENVY x360 Convertible 13-ay1xxx/8929, BIOS F.01 07/14/2021
[  +0.000004] RIP: 0010:i2c_transfer+0xd/0x100
[  +0.000011] Code: ea fc ff ff 66 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 41 54 55 53 <48> 8b 47 10 48 89 fb 48 83 38 00 0f 84 b3 00 00 00 83 3d 2f 80 16
[  +0.000004] RSP: 0018:ffff9c4f89c0fad0 EFLAGS: 00010246
[  +0.000005] RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000000080
[  +0.000003] RDX: 0000000000000002 RSI: ffff9c4f89c0fb20 RDI: 00000000000004b0
[  +0.000003] RBP: ffff9c4f89c0fb80 R08: 0000000000000080 R09: ffff8d8e0b15b980
[  +0.000003] R10: 00000000000380e0 R11: 0000000000000000 R12: 0000000000000080
[  +0.000002] R13: 0000000000000002 R14: ffff9c4f89c0fb0e R15: ffff9c4f89c0fb0f
[  +0.000004] FS:  00007f9ad2176c40(0000) GS:ffff8d90fe9c0000(0000) knlGS:0000000000000000
[  +0.000003] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  +0.000004] CR2: 00000000000004c0 CR3: 0000000121bc4000 CR4: 0000000000750ee0
[  +0.000003] PKRU: 55555554
[  +0.000003] Call Trace:
[  +0.000006]  <TASK>
[  +0.000006]  ? __die+0x23/0x70
[  +0.000011]  ? page_fault_oops+0x17d/0x4c0
[  +0.000008]  ? preempt_count_add+0x6e/0xa0
[  +0.000008]  ? srso_alias_return_thunk+0x5/0x7f
[  +0.000011]  ? exc_page_fault+0x7f/0x180
[  +0.000009]  ? asm_exc_page_fault+0x26/0x30
[  +0.000013]  ? i2c_transfer+0xd/0x100
[  +0.000010]  drm_do_probe_ddc_edid+0xc2/0x140 [drm]
[  +0.000067]  ? srso_alias_return_thunk+0x5/0x7f
[  +0.000006]  ? _drm_do_get_edid+0x97/0x3c0 [drm]
[  +0.000043]  ? __pfx_drm_do_probe_ddc_edid+0x10/0x10 [drm]
[  +0.000042]  edid_block_read+0x3b/0xd0 [drm]
[  +0.000043]  _drm_do_get_edid+0xb6/0x3c0 [drm]
[  +0.000041]  ? __pfx_drm_do_probe_ddc_edid+0x10/0x10 [drm]
[  +0.000043]  drm_edid_read_custom+0x37/0xd0 [drm]
[  +0.000044]  amdgpu_dm_connector_mode_valid+0x129/0x1d0 [amdgpu]
[  +0.000153]  drm_connector_mode_valid+0x3b/0x60 [drm_kms_helper]
[  +0.000000]  __drm_helper_update_and_validate+0xfe/0x3c0 [drm_kms_helper]
[  +0.000000]  ? amdgpu_dm_connector_get_modes+0xb6/0x520 [amdgpu]
[  +0.000000]  ? srso_alias_return_thunk+0x5/0x7f
[  +0.000000]  drm_helper_probe_single_connector_modes+0x2ab/0x540 [drm_kms_helper]
[  +0.000000]  status_store+0xb2/0x1f0 [drm]
[  +0.000000]  kernfs_fop_write_iter+0x136/0x1d0
[  +0.000000]  vfs_write+0x24d/0x440
[  +0.000000]  ksys_write+0x6f/0xf0
[  +0.000000]  do_syscall_64+0x60/0xc0
[  +0.000000]  ? srso_alias_return_thunk+0x5/0x7f
[  +0.000000]  ? syscall_exit_to_user_mode+0x2b/0x40
[  +0.000000]  ? srso_alias_return_thunk+0x5/0x7f
[  +0.000000]  ? do_syscall_64+0x6c/0xc0
[  +0.000000]  ? do_syscall_64+0x6c/0xc0
[  +0.000000]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[  +0.000000] RIP: 0033:0x7f9ad46b4b00
[  +0.000000] Code: 40 00 48 8b 15 19 b3 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d e1 3a 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89
[  +0.000000] RSP: 002b:00007ffcbd3bd6d8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
[  +0.000000] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9ad46b4b00
[  +0.000000] RDX: 0000000000000002 RSI: 00007f9ad48a7417 RDI: 0000000000000009
[  +0.000000] RBP: 0000000000000002 R08
---truncated---
CVSS v3.1: 5.5