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Check SetMap request length carefully. 

Avoid out of bounds memory accesses on too short request.

ZDI-CAN 11572 /  CVE-2020-14360

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>
This commit is contained in:
Matthieu Herrb 2020-11-12 19:15:07 +01:00
parent 87c64fc5b0
commit 446ff2d317
1 changed files with 92 additions and 0 deletions
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92
xkb/xkb.c
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@ -2382,6 +2382,93 @@ SetVirtualModMap(XkbSrvInfoPtr xkbi,
return (char *) wire;
}
#define _add_check_len(new) \
if (len > UINT32_MAX - (new) || len > req_len - (new)) goto bad; \
else len += new
/**
* Check the length of the SetMap request
*/
static int
_XkbSetMapCheckLength(xkbSetMapReq *req)
{
size_t len = sz_xkbSetMapReq, req_len = req->length << 2;
xkbKeyTypeWireDesc *keytype;
xkbSymMapWireDesc *symmap;
BOOL preserve;
int i, map_count, nSyms;
if (req_len < len)
goto bad;
/* types */
if (req->present & XkbKeyTypesMask) {
keytype = (xkbKeyTypeWireDesc *)(req + 1);
for (i = 0; i < req->nTypes; i++) {
_add_check_len(XkbPaddedSize(sz_xkbKeyTypeWireDesc));
if (req->flags & XkbSetMapResizeTypes) {
_add_check_len(keytype->nMapEntries
* sz_xkbKTSetMapEntryWireDesc);
preserve = keytype->preserve;
map_count = keytype->nMapEntries;
if (preserve) {
_add_check_len(map_count * sz_xkbModsWireDesc);
}
keytype += 1;
keytype = (xkbKeyTypeWireDesc *)
((xkbKTSetMapEntryWireDesc *)keytype + map_count);
if (preserve)
keytype = (xkbKeyTypeWireDesc *)
((xkbModsWireDesc *)keytype + map_count);
}
}
}
/* syms */
if (req->present & XkbKeySymsMask) {
symmap = (xkbSymMapWireDesc *)((char *)req + len);
for (i = 0; i < req->nKeySyms; i++) {
_add_check_len(sz_xkbSymMapWireDesc);
nSyms = symmap->nSyms;
_add_check_len(nSyms*sizeof(CARD32));
symmap += 1;
symmap = (xkbSymMapWireDesc *)((CARD32 *)symmap + nSyms);
}
}
/* actions */
if (req->present & XkbKeyActionsMask) {
_add_check_len(req->totalActs * sz_xkbActionWireDesc
+ XkbPaddedSize(req->nKeyActs));
}
/* behaviours */
if (req->present & XkbKeyBehaviorsMask) {
_add_check_len(req->totalKeyBehaviors * sz_xkbBehaviorWireDesc);
}
/* vmods */
if (req->present & XkbVirtualModsMask) {
_add_check_len(XkbPaddedSize(Ones(req->virtualMods)));
}
/* explicit */
if (req->present & XkbExplicitComponentsMask) {
/* two bytes per non-zero explicit componen */
_add_check_len(XkbPaddedSize(req->totalKeyExplicit * sizeof(CARD16)));
}
/* modmap */
if (req->present & XkbModifierMapMask) {
/* two bytes per non-zero modmap component */
_add_check_len(XkbPaddedSize(req->totalModMapKeys * sizeof(CARD16)));
}
/* vmodmap */
if (req->present & XkbVirtualModMapMask) {
_add_check_len(req->totalVModMapKeys * sz_xkbVModMapWireDesc);
}
if (len == req_len)
return Success;
bad:
ErrorF("[xkb] BOGUS LENGTH in SetMap: expected %ld got %ld\n",
len, req_len);
return BadLength;
}
/**
* Check if the given request can be applied to the given device but don't
* actually do anything, except swap values when client->swapped and doswap are both true.
@ -2642,6 +2729,11 @@ ProcXkbSetMap(ClientPtr client)
CHK_KBD_DEVICE(dev, stuff->deviceSpec, client, DixManageAccess);
CHK_MASK_LEGAL(0x01, stuff->present, XkbAllMapComponentsMask);
/* first verify the request length carefully */
rc = _XkbSetMapCheckLength(stuff);
if (rc != Success)
return rc;
tmp = (char *) &stuff[1];
/* Check if we can to the SetMap on the requested device. If this