[Bug 240272] bhyve/pci_fbuf.c: gc_image NULL pointer dereference

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240272

            Bug ID: 240272
           Summary: bhyve/pci_fbuf.c: gc_image NULL pointer dereference
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: bhyve
          Assignee: virtualization at FreeBSD.org
          Reporter: mohdfakhrizulkifli at gmail.com

Created attachment 207095
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=207095&action=edit
pci_fbuf.patch

The sc->gc_image at line 166 and line 172 can be NULL. Dereference it can cause
a segmentation fault. This is unlikely to happen without root privilege as the
driver must first be loaded in order to interact with the pci_fbuf. However,
the checking for NULL should be handled within the pci_fbuf itself and not
relying on the driver loaded.

File: pci_fbuf.c
166:     if (!sc->gc_image->vgamode && sc->memregs.width == 0 &&
167:         sc->memregs.height == 0) {
168:         DPRINTF(DEBUG_INFO, ("switching to VGA mode\r\n"));
169:         sc->gc_image->vgamode = 1;
170:         sc->gc_width = 0;
171:         sc->gc_height = 0;
172:     } else if (sc->gc_image->vgamode && sc->memregs.width != 0 &&
173:         sc->memregs.height != 0) {
174:         DPRINTF(DEBUG_INFO, ("switching to VESA mode\r\n"));
175:         sc->gc_image->vgamode = 0;
176:     } 

Proof-of-Crash:
Thread 13 "vcpu 2" received signal SIGSEGV, Segmentation fault.
[Switching to LWP 100571 of process 4094]
0x0000000000231802 in pci_fbuf_write (ctx=<optimized out>, vcpu=<optimized
out>, pi=<optimized out>, baridx=<optimized out>, offset=<optimized out>,
size=<optimized out>,
 value=1953719668) at /usr/src/usr.sbin/bhyve/pci_fbuf.c:166
166     if (!sc->gc_image->vgamode && sc->memregs.width == 0 &&
(gdb) p sc->gc_image
$1 = (struct bhyvegc_image *) 0x0
(gdb) bt
#0 0x0000000000231802 in pci_fbuf_write (ctx=<optimized out>, vcpu=<optimized
out>, pi=<optimized out>, baridx=<optimized out>, offset=<optimized out>,
size=<optimized out>,
 value=1953719668) at /usr/src/usr.sbin/bhyve/pci_fbuf.c:166
#1 0x0000000000230522 in pci_emul_mem_handler (ctx=0x80028e080, vcpu=2,
dir=<optimized out>, addr=<optimized out>, size=4, val=0x7fffde9f2d40,
arg1=0x800a9aa00, arg2=0)
 at /usr/src/usr.sbin/bhyve/pci_emul.c:415
#2 0x0000000000224ae4 in mem_write (ctx=0x80028e080, vcpu=2, gpa=3,
wval=1953719668, size=0, arg=0x0) at /usr/src/usr.sbin/bhyve/mem.c:162
#3 0x00000000002486ae in emulate_mov (vm=<optimized out>, vcpuid=<optimized
out>, gpa=<optimized out>, vie=<optimized out>, memread=<optimized out>,
 memwrite=<optimized out>, arg=<optimized out>) at
/usr/src/sys/amd64/vmm/vmm_instruction_emul.c:517
#4 vmm_emulate_instruction (vm=<optimized out>, vcpuid=<optimized out>,
gpa=<optimized out>, vie=<optimized out>, paging=<optimized out>,
memread=<optimized out>,
 memwrite=0x224ab0 <mem_write>, memarg=0x800aad100) at
/usr/src/sys/amd64/vmm/vmm_instruction_emul.c:1510
#5 0x000000000022448f in emulate_mem_cb (ctx=0x80028e080, vcpu=2,
paddr=34370857472, mr=0x0, arg=<optimized out>) at
/usr/src/usr.sbin/bhyve/mem.c:238
#6 0x00000000002243da in access_memory (ctx=0x80028e080, vcpu=2,
paddr=3221241856, cb=0x224470 <emulate_mem_cb>, arg=0x7fffde9f2ec8) at
/usr/src/usr.sbin/bhyve/mem.c:215
#7 0x00000000002242b9 in emulate_mem (ctx=0x80028e080, vcpu=2,
paddr=34370857472, vie=<optimized out>, paging=<optimized out>) at
/usr/src/usr.sbin/bhyve/mem.c:251
#8 0x000000000021bc75 in vmexit_inst_emul (ctx=0x80028e080, vmexit=0x24f780
<vmexit+272>, pvcpu=<optimized out>) at /usr/src/usr.sbin/bhyve/bhyverun.c:630
#9 0x000000000021b6da in vm_loop (ctx=0x80028e080, vcpu=2, startrip=<optimized
out>) at /usr/src/usr.sbin/bhyve/bhyverun.c:748
#10 0x000000000021a969 in fbsdrun_start_thread (param=0x24e050
<mt_vmm_info+48>) at /usr/src/usr.sbin/bhyve/bhyverun.c:353
#11 0x000000080061b776 in ?? () from /lib/libthr.so.3
#12 0x0000000000000000 in ?? ()
Backtrace stopped: Cannot access memory at address 0x7fffde9f3000

-- 
You are receiving this mail because:
You are the assignee for the bug.