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

scsi: xen/scsifront: Check for a NULL shadow entry on a backend response

scsifront_do_response() validates the rqid in a backend response against VSCSIIF_MAX_REQS before using it to index info->shadow[], but then dereferences the entry to test ->inflight without checking that the slot is populated. Shadow slots are NULL before a command is submitted (the host private area is zeroed at allocation) and are reset to NULL in _scsifront_put_rqid() once a request completes, so an in-range rqid that does not correspond to an outstanding request makes the frontend dereference a NULL pointer.

A malicious or buggy backend can thus crash the guest by returning a response whose rqid is in range but not in flight -- for example a spurious response before any command has been issued, or a duplicate of one already completed. The ring has only VSCSIIF_MAX_REQS (16) slots, so before the first command every in-range rqid selects a NULL slot.

Reject a response whose shadow slot is not populated.

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

scsi: xen/scsifront: Check for a NULL shadow entry on a backend response

scsifront_do_response() validates the rqid in a backend response against VSCSIIF_MAX_REQS before using it to index info->shadow[], but then dereferences the entry to test ->inflight without checking that the slot is populated. Shadow slots are NULL before a command is submitted (the host private area is zeroed at allocation) and are reset to NULL in _scsifront_put_rqid() once a request completes, so an in-range rqid that does not correspond to an outstanding request makes the frontend dereference a NULL pointer.

A malicious or buggy backend can thus crash the guest by returning a response whose rqid is in range but not in flight -- for example a spurious response before any command has been issued, or a duplicate of one already completed. The ring has only VSCSIIF_MAX_REQS (16) slots, so before the first command every in-range rqid selects a NULL slot.

Reject a response whose shadow slot is not populated.

Affected: Ubuntu:16.04:LTS: linux-hwe-edge, Ubuntu:18.04:LTS: linux-aws-5.0, Ubuntu:18.04:LTS: linux-aws-5.3, Ubuntu:18.04:LTS: linux-azure, Ubuntu:18.04:LTS: linux-azure-5.3, Ubuntu:18.04:LTS: linux-azure-edge, Ubuntu:18.04:LTS: linux-gcp, Ubuntu:18.04:LTS: linux-gcp-5.3, Ubuntu:18.04:LTS: linux-gke-4.15, Ubuntu:18.04:LTS: linux-gke-5.4 and 164 more

In the Linux kernel, the following vulnerability has been resolved: scsi: xen/scsifront: Check for a NULL shadow entry on a backend response scsifront_do_response() validates the rqid in a backend response against VSCSIIF_MAX_REQS before using it to index info->shadow[], but then dereferences the entry to test ->inflight without checking that the slot is populated. Shadow slots are NULL before a command is submitted (the host private area is zeroed at allocation) and are reset to NULL in _scsifront_put_rqid() once a request completes, so an in-range rqid that does not correspond to an outstanding request makes the frontend dereference a NULL pointer. A malicious or buggy backend can thus crash the guest by returning a response whose rqid is in range but not in flight -- for example a spurious response before any command has been issued, or a duplicate of one already completed. The ring has only VSCSIIF_MAX_REQS (16) slots, so before the first command every in-range rqid selects a NULL slot. Reject a response whose shadow slot is not populated.

Ein Angreifer kann mehrere Schwachstellen im Linux Kernel ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen, möglicherweise einen Denial-of-Service-Angriff auszulösen, Daten zu manipulieren oder offenzulegen oder Sicherheitsmaßnahmen zu umgehen.