From ea8239650656846d810a93e7659e182e412f07b3 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Sun, 9 Jun 2013 11:13:42 -0700 Subject: libX11: check size of GetReqExtra after XFlush Two users of GetReqExtra pass arbitrarily sized allocations from the caller (ModMap and Host). Adjust _XGetRequest() (called by the GetReqExtra macro) to double-check the requested length and invalidate "req" when this happens. Users of GetReqExtra passing lengths greater than the Xlib buffer size (normally 16K) must check "req" and fail gracefully instead of crashing. Any callers of GetReqExtra that do not check "req" for NULL will experience this change, in the pathological case, as a NULL dereference instead of a buffer overflow. This is an improvement, but the documentation for GetReqExtra has been updated to reflect the need to check the value of "req" after the call. Bug that manifested the problem: https://bugs.launchpad.net/ubuntu/+source/x11-xserver-utils/+bug/792628 Signed-off-by: Kees Cook Reviewed-by: Alan Coopersmith Signed-off-by: Alan Coopersmith Backported-to-NX-by: Ulrich Sibiller --- nx-X11/lib/X11/ModMap.c | 10 +++++++--- nx-X11/lib/X11/XlibInt.c | 8 ++++++++ 2 files changed, 15 insertions(+), 3 deletions(-) (limited to 'nx-X11/lib/X11') diff --git a/nx-X11/lib/X11/ModMap.c b/nx-X11/lib/X11/ModMap.c index 04cd676eb..3c6971c77 100644 --- a/nx-X11/lib/X11/ModMap.c +++ b/nx-X11/lib/X11/ModMap.c @@ -65,9 +65,9 @@ XGetModifierMapping(register Display *dpy) /* * Returns: - * 0 Success - * 1 Busy - one or more old or new modifiers are down - * 2 Failed - one or more new modifiers unacceptable + * MappingSuccess (0) Success + * MappingBusy (1) Busy - one or more old or new modifiers are down + * MappingFailed (2) Failed - one or more new modifiers unacceptable */ int XSetModifierMapping( @@ -80,6 +80,10 @@ XSetModifierMapping( LockDisplay(dpy); GetReqExtra(SetModifierMapping, mapSize, req); + if (!req) { + UnlockDisplay(dpy); + return MappingFailed; + } req->numKeyPerModifier = modifier_map->max_keypermod; diff --git a/nx-X11/lib/X11/XlibInt.c b/nx-X11/lib/X11/XlibInt.c index 564d318fc..deab8b3ad 100644 --- a/nx-X11/lib/X11/XlibInt.c +++ b/nx-X11/lib/X11/XlibInt.c @@ -3980,6 +3980,14 @@ void *_XGetRequest(Display *dpy, CARD8 type, size_t len) if (dpy->bufptr + len > dpy->bufmax) _XFlush(dpy); + /* Request still too large, so do not allow it to overflow. */ + if (dpy->bufptr + len > dpy->bufmax) { + fprintf(stderr, + "Xlib: request %d length %zd would exceed buffer size.\n", + type, len); + /* Changes failure condition from overflow to NULL dereference. */ + return NULL; + } if (len % 4) fprintf(stderr, -- cgit v1.2.3