ctl: limit memory allocation in pci_virtio_scsi

The virtio_scsi device allows a VM guest to directly send SCSI commands
(ctsio->cdb array) to the kernel driver exposed on /dev/cam/ctl
(ctl.ko).

All kernel commands accessible from the guest are defined by
ctl_cmd_table.

The command ctl_persistent_reserve_out (cdb[0]=0x5F and cbd[1]=0) allows
the caller to call malloc() with an arbitrary size (uint32_t). This can
be used by the guest to overload the kernel memory (DOS attack).

Reported by:    Synacktiv
Reviewed by:	asomers
Security:       HYP-08
Sponsored by:   The Alpha-Omega Project
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D46044

(cherry picked from commit 64b0f52be2c9d7bcecebfeef393f8ec56cb85f47)

1 files changed, 12 insertions, 0 deletions

diff --git a/sys/cam/ctl/ctl.c b/sys/cam/ctl/ctl.c
index de759f81bc86..5c33645f0f0d 100644
--- a/sys/cam/ctl/ctl.c
+++ b/sys/cam/ctl/ctl.c
@@ -8314,6 +8314,18 @@ ctl_persistent_reserve_out(struct ctl_scsiio *ctsio)
 
 	param_len = scsi_4btoul(cdb->length);
 
+	/* validate the parameter length */
+	if (param_len != 24) {
+		ctl_set_invalid_field(ctsio,
+				/*sks_valid*/ 1,
+				/*command*/ 1,
+				/*field*/ 5,
+				/*bit_valid*/ 1,
+				/*bit*/ 0);
+		ctl_done((union ctl_io *)ctsio);
+		return (CTL_RETVAL_COMPLETE);
+	}
+
 	if ((ctsio->io_hdr.flags & CTL_FLAG_ALLOCATED) == 0) {
 		ctsio->kern_data_ptr = malloc(param_len, M_CTL, M_WAITOK);
 		ctsio->kern_data_len = param_len;