CVE-2024-49863

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

vhost/scsi: null-ptr-dereference in vhost_scsi_get_req()

Since commit 3f8ca2e115e5 (vhost/scsi: Extract common handling code from control queue handler) a null pointer dereference bug can be triggered when guest sends an SCSI AN request.

In vhost_scsi_ctl_handle_vq(), vc.target is assigned with &v_req.tmf.lun[1] within a switch-case block and is then passed to vhost_scsi_get_req() which extracts vc->req and tpg. However, for a VIRTIO_SCSI_T_AN_* request, tpg is not required, so vc.target is set to NULL in this branch. Later, in vhost_scsi_get_req(), vc->target is dereferenced without being checked, leading to a null pointer dereference bug. This bug can be triggered from guest.

When this bug occurs, the vhost_worker process is killed while holding vq->mutex and the corresponding tpg will remain occupied indefinitely.

Below is the KASAN report: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 1 PID: 840 Comm: poc Not tainted 6.10.0+ #1 Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:vhost_scsi_get_req+0x165/0x3a0 Code: 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 2b 02 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b 65 30 4c 89 e2 48 c1 ea 03 <0f> b6 04 02 4c 89 e2 83 e2 07 38 d0 7f 08 84 c0 0f 85 be 01 00 00 RSP: 0018:ffff888017affb50 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: ffff88801b000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff888017affcb8 RBP: ffff888017affb80 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: ffff888017affc88 R14: ffff888017affd1c R15: ffff888017993000 FS: 000055556e076500(0000) GS:ffff88806b100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000200027c0 CR3: 0000000010ed0004 CR4: 0000000000370ef0 Call Trace: ? show_regs+0x86/0xa0 ? die_addr+0x4b/0xd0 ? exc_general_protection+0x163/0x260 ? asm_exc_general_protection+0x27/0x30 ? vhost_scsi_get_req+0x165/0x3a0 vhost_scsi_ctl_handle_vq+0x2a4/0xca0 ? __pfx_vhost_scsi_ctl_handle_vq+0x10/0x10 ? __switch_to+0x721/0xeb0 ? __schedule+0xda5/0x5710 ? __kasan_check_write+0x14/0x30 ? _raw_spin_lock+0x82/0xf0 vhost_scsi_ctl_handle_kick+0x52/0x90 vhost_run_work_list+0x134/0x1b0 vhost_task_fn+0x121/0x350 … —[ end trace 0000000000000000 ]—

Lets add a check in vhost_scsi_get_req.

[whitespace fixes]

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/00fb5b23e1c9cdbe496f5cd6b40367cb895f6c93
• https://git.kernel.org/stable/c/221af82f606d928ccef19a16d35633c63026f1be
• https://git.kernel.org/stable/c/25613e6d9841a1f9fb985be90df921fa99f800de
• https://git.kernel.org/stable/c/46128370a72c431df733af5ebb065c4d48c9ad39
• https://git.kernel.org/stable/c/61517f33e76d2c5247c1e61e668693afe5b67e6f
• https://git.kernel.org/stable/c/6592347f06e2b19a624270a85ad4b3ae48c3b241
• https://git.kernel.org/stable/c/ace9c778a214da9c98d7b69d904d1b0816f4f681