OpenE2K/qemu-e2k
13
4
Fork 0
Code Issues 4 Pull Requests Projects 2 Releases Activity

vnc: fix memory corruption (CVE-2015-5225)

Browse Source 
The _cmp_bytes variable added by commit "bea60dd ui/vnc: fix potential
memory corruption issues" can become negative.  Result is (possibly
exploitable) memory corruption.  Reason for that is it uses the stride
instead of bytes per scanline to apply limits.

For the server surface is is actually fine.  vnc creates that itself,
there is never any padding and thus scanline length always equals stride.

For the guest surface scanline length and stride are typically identical
too, but it doesn't has to be that way.  So add and use a new variable
(guest_ll) for the guest scanline length.  Also rename min_stride to
line_bytes to make more clear what it actually is.  Finally sprinkle
in an assert() to make sure we never use a negative _cmp_bytes again.

Reported-by: 范祚至(库特) <zuozhi.fzz@alibaba-inc.com>
Reviewed-by: P J P <ppandit@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Gerd Hoffmann 2015-08-17 19:56:53 +02:00
parent 7df9671989
commit eb8934b041
1 changed files with 10 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
ui/vnc.c
View File

@ -2872,7 +2872,7 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
pixman_image_get_width(vd->server));
int height = MIN(pixman_image_get_height(vd->guest.fb),
pixman_image_get_height(vd->server));
int cmp_bytes, server_stride, min_stride, guest_stride, y = 0;
int cmp_bytes, server_stride, line_bytes, guest_ll, guest_stride, y = 0;
uint8_t *guest_row0 = NULL, *server_row0;
VncState *vs;
int has_dirty = 0;
@ -2891,17 +2891,21 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
* Update server dirty map.
*/
server_row0 = (uint8_t *)pixman_image_get_data(vd->server);
server_stride = guest_stride = pixman_image_get_stride(vd->server);
server_stride = guest_stride = guest_ll =
pixman_image_get_stride(vd->server);
cmp_bytes = MIN(VNC_DIRTY_PIXELS_PER_BIT * VNC_SERVER_FB_BYTES,
server_stride);
if (vd->guest.format != VNC_SERVER_FB_FORMAT) {
int width = pixman_image_get_width(vd->server);
tmpbuf = qemu_pixman_linebuf_create(VNC_SERVER_FB_FORMAT, width);
} else {
int guest_bpp =
PIXMAN_FORMAT_BPP(pixman_image_get_format(vd->guest.fb));
guest_row0 = (uint8_t *)pixman_image_get_data(vd->guest.fb);
guest_stride = pixman_image_get_stride(vd->guest.fb);
guest_ll = pixman_image_get_width(vd->guest.fb) * ((guest_bpp + 7) / 8);
}
min_stride = MIN(server_stride, guest_stride);
line_bytes = MIN(server_stride, guest_ll);
for (;;) {
int x;
@ -2932,9 +2936,10 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
if (!test_and_clear_bit(x, vd->guest.dirty[y])) {
continue;
}
if ((x + 1) * cmp_bytes > min_stride) {
_cmp_bytes = min_stride - x * cmp_bytes;
if ((x + 1) * cmp_bytes > line_bytes) {
_cmp_bytes = line_bytes - x * cmp_bytes;
}
assert(_cmp_bytes >= 0);
if (memcmp(server_ptr, guest_ptr, _cmp_bytes) == 0) {
continue;
}