CVE-2024-49863

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

vhost/scsi: null-ptr-dereference in vhostscsiget_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 vhostscsictlhandlevq(), vc.target is assigned with &v_req.tmf.lun[1] within a switch-case block and is then passed to vhostscsigetreq() 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 vhostscsigetreq(), 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:vhostscsigetreq+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: <TASK> ? showregs+0x86/0xa0 ? dieaddr+0x4b/0xd0 ? excgeneralprotection+0x163/0x260 ? asmexcgeneralprotection+0x27/0x30 ? vhostscsigetreq+0x165/0x3a0 vhostscsictlhandle_vq+0x2a4/0xca0 ? __pfxvhostscsictlhandle_vq+0x10/0x10 ? __switch_to+0x721/0xeb0 ? __schedule+0xda5/0x5710 ? __kasancheckwrite+0x14/0x30 ? rawspinlock+0x82/0xf0 vhostscsictlhandlekick+0x52/0x90 vhostrunworklist+0x134/0x1b0 vhosttaskfn+0x121/0x350 ... </TASK> ---[ end trace 0000000000000000 ]---

Let's add a check in vhostscsiget_req.

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