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memslot: Fix off-by-one error in group/slot boundary check

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RedMemSlotInfo keeps an array of groups, and each group contains an
array of slots. Unfortunately, these checks are off by 1, they check
that the index is greater or equal to the number of elements in the
array, while these arrays are 0 based. The check should only check for
strictly greater than the number of elements.

For the group array, this is not a big issue, as these memslot groups
are created by spice-server users (eg QEMU), and the group ids used to
index that array are also generated by the spice-server user, so it
should not be possible for the guest to set them to arbitrary values.

The slot id is more problematic, as it's calculated from a QXLPHYSICAL
address, and such addresses are usually set by the guest QXL driver, so
the guest can set these to arbitrary values, including malicious values,
which are probably easy to build from the guest PCI configuration.

This patch fixes the arrays bound check, and adds a test case for this.
This fixes CVE-2019-3813.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
Acked-by: Frediano Ziglio <fziglio@redhat.com>
This commit is contained in:
Christophe Fergeau 2018-11-29 14:18:39 +01:00
parent 03d46e9e19
commit a4a16ac42d
2 changed files with 32 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
server/memslot.c
View File

@ -97,13 +97,13 @@ void *memslot_get_virt(RedMemSlotInfo *info, QXLPHYSICAL addr, uint32_t add_size
MemSlot *slot;
if (group_id > info->num_memslots_groups) {
if (group_id >= info->num_memslots_groups) {
spice_critical("group_id too big");
return NULL;
}
slot_id = memslot_get_id(info, addr);
if (slot_id > info->num_memslots) {
if (slot_id >= info->num_memslots) {
print_memslots(info);
spice_critical("slot_id %d too big, addr=%" PRIx64, slot_id, addr);
return NULL;

30
server/tests/test-qxl-parsing.c
View File

@ -85,6 +85,31 @@ static void deinit_qxl_surface(QXLSurfaceCmd *qxl)
g_free(from_physical(qxl->u.surface_create.data));
}
static void test_memslot_invalid_group_id(void)
{
RedMemSlotInfo mem_info;
init_meminfo(&mem_info);
memslot_get_virt(&mem_info, 0, 16, 1);
}
static void test_memslot_invalid_slot_id(void)
{
RedMemSlotInfo mem_info;
init_meminfo(&mem_info);
memslot_get_virt(&mem_info, 1 << mem_info.memslot_id_shift, 16, 0);
}
static void test_memslot_invalid_addresses(void)
{
g_test_trap_subprocess("/server/memslot-invalid-addresses/subprocess/group_id", 0, 0);
g_test_trap_assert_stderr("*group_id too big*");
g_test_trap_subprocess("/server/memslot-invalid-addresses/subprocess/slot_id", 0, 0);
g_test_trap_assert_stderr("*slot_id 1 too big*");
}
static void test_no_issues(void)
{
RedMemSlotInfo mem_info;
@ -269,6 +294,11 @@ int main(int argc, char *argv[])
{
g_test_init(&argc, &argv, NULL);
/* try to use invalid memslot group/slot */
g_test_add_func("/server/memslot-invalid-addresses", test_memslot_invalid_addresses);
g_test_add_func("/server/memslot-invalid-addresses/subprocess/group_id", test_memslot_invalid_group_id);
g_test_add_func("/server/memslot-invalid-addresses/subprocess/slot_id", test_memslot_invalid_slot_id);
/* try to create a surface with no issues, should succeed */
g_test_add_func("/server/qxl-parsing-no-issues", test_no_issues);