From a2ee4c357e901e111f8dbfb940342581aeed2df1 Mon Sep 17 00:00:00 2001 From: Matthieu Herrb Date: Tue, 4 Oct 2016 15:03:49 +0000 Subject: Avoid OOB write in XRenderQueryFilters The memory for filter names is reserved right after receiving the reply. After that, filters are iterated and each individual filter name is stored in that reserved memory. The individual name lengths are not checked for validity, which means that a malicious server can reserve less memory than it will write to during each iteration. From Tobias Stoeckmann / X.Org security advisory Oct 4, 2016 --- lib/libXrender/src/Filter.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/lib/libXrender/src/Filter.c b/lib/libXrender/src/Filter.c index edfa57231..8d701eb98 100644 --- a/lib/libXrender/src/Filter.c +++ b/lib/libXrender/src/Filter.c @@ -38,7 +38,7 @@ XRenderQueryFilters (Display *dpy, Drawable drawable) char *name; char len; int i; - unsigned long nbytes, nbytesAlias, nbytesName; + unsigned long nbytes, nbytesAlias, nbytesName, reply_left; if (!RenderHasExtension (info)) return NULL; @@ -114,6 +114,7 @@ XRenderQueryFilters (Display *dpy, Drawable drawable) * Read the filter aliases */ _XRead16Pad (dpy, filters->alias, 2 * rep.numAliases); + reply_left = 8 + rep.length - 2 * rep.numAliases;; /* * Read the filter names @@ -122,9 +123,19 @@ XRenderQueryFilters (Display *dpy, Drawable drawable) { int l; _XRead (dpy, &len, 1); + reply_left--; l = len & 0xff; + if ((unsigned long)l + 1 > nbytesName) { + _XEatDataWords(dpy, reply_left); + Xfree(filters); + UnlockDisplay (dpy); + SyncHandle (); + return NULL; + } + nbytesName -= l + 1; filters->filter[i] = name; _XRead (dpy, name, l); + reply_left -= l; name[l] = '\0'; name += l + 1; } -- cgit v1.2.3