The scope of this bug is somewhat limited. It depends on a particular
multiplication overflowing:
nodesize = c * elsize;
In order for this to happen, you must have
maxsize>max(nodesize)*elsize; otherwise the c>maxsize check will catch
it. Hence the patch:
- if ((c > maxsize) && (xdrs->x_op != XDR_FREE)) {
+ if ((c > maxsize || UINT_MAX/elsize < c) &&
+ (xdrs->x_op != XDR_FREE)) {
In practice, there are only two ways that this constraint is violated:
1) An application explicitly passes in a large maxsize. I generally
consider this an application bug, in the same vain as sending bogus
arguments to calloc(), fread()/fwrite() or qsort(). However, amd
and various amd utilities -- amd, amq, pawd, and probably others --
pass in a maxsize ~0 (i.e. all-1s) and are therefore susceptible.
2) A program uses rpcgen with unbounded arrays; e.g. in rex.x:
rexstring rst_cmd<>; /* list of command and args */
rexstring rst_env<>; /* list of environment */
(Note that nothing in our source tree actually *uses* rex.x, but
the same problems occurs in rusers.x.)
There are only a few things in our source tree that actually use
xdr_array():
/usr/src/dist/am-utils/amd/amq_subr.c
/usr/src/dist/am-utils/amq/amq_xdr.c
/usr/src/dist/am-utils/libamu/xdr_func.c
/usr/src/gnu/dist/toolchain/gdb/vx-share/xdr_ld.c
/usr/src/gnu/dist/toolchain/gdb/vx-share/xdr_rdb.c
/usr/src/lib/libc/rpc/authunix_prot.c
/usr/src/lib/librpcsvc/rnusers.x
/usr/obj.i386/lib/librpcsvc/rex.c
/usr/obj.i386/lib/librpcsvc/rnusers.c
/usr/obj.i386/lib/librpcsvc/rusers.c
/usr/obj.i386/usr.sbin/rpc.pcnfsd/pcnfsd_xdr.c
The GDB stuff and rex.c are not actually linked into anything. The
uses in authunix_prot.c, rnusers.c and pcnfsd_xdr.c are all
sufficiently bounded. Ergo, the only vulnerable programs are
amd/amq/etc. and rusers (the client, not the server).
Received on Aug 01 2002
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