Re: [PATCH v2 4/4] CVE-2022-23218: Buffer overflow in sunrpc svcunix_create (bug 28768)

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 14/01/2022 13:54, Florian Weimer via Libc-alpha wrote:
> The sunrpc function svcunix_create suffers from a stack-based buffer
> overflow with overlong pathname arguments.
> ---
>   NEWS                  |  3 +++
>   sunrpc/Makefile       |  2 +-
>   sunrpc/svc_unix.c     | 11 ++++-------
>   sunrpc/tst-bug28768.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 50 insertions(+), 8 deletions(-)
>   create mode 100644 sunrpc/tst-bug28768.c
> 

LGTM.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> diff --git a/NEWS b/NEWS
> index 94248b580d..85ec7e4c6a 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -154,6 +154,9 @@ Security related changes:
>     legacy function could result in a stack-based buffer overflow when
>     using the "unix" protocol.  Reported by Martin Sebor.
>   
> +  CVE-2022-23218: Passing an overlong file name to the svcunix_create
> +  legacy function could result in a stack-based buffer overflow.
> +
>   The following bugs are resolved with this release:
>   
>     [The release manager will add the list generated by
> diff --git a/sunrpc/Makefile b/sunrpc/Makefile
> index 183ef3dc55..a79a7195fc 100644
> --- a/sunrpc/Makefile
> +++ b/sunrpc/Makefile
> @@ -65,7 +65,7 @@ shared-only-routines = $(routines)
>   endif
>   
>   tests = tst-xdrmem tst-xdrmem2 test-rpcent tst-udp-error tst-udp-timeout \
> -  tst-udp-nonblocking tst-bug22542
> +  tst-udp-nonblocking tst-bug22542 tst-bug28768
>   
>   xtests := tst-getmyaddr
>   
> diff --git a/sunrpc/svc_unix.c b/sunrpc/svc_unix.c
> index f2280b4c49..67177a2e78 100644
> --- a/sunrpc/svc_unix.c
> +++ b/sunrpc/svc_unix.c
> @@ -154,7 +154,10 @@ svcunix_create (int sock, u_int sendsize, u_int recvsize, char *path)
>     SVCXPRT *xprt;
>     struct unix_rendezvous *r;
>     struct sockaddr_un addr;
> -  socklen_t len = sizeof (struct sockaddr_in);
> +  socklen_t len = sizeof (addr);
> +
> +  if (__sockaddr_un_set (&addr, path) < 0)
> +    return NULL;
>   
>     if (sock == RPC_ANYSOCK)
>       {
> @@ -165,12 +168,6 @@ svcunix_create (int sock, u_int sendsize, u_int recvsize, char *path)
>   	}
>         madesock = TRUE;
>       }
> -  memset (&addr, '\0', sizeof (addr));
> -  addr.sun_family = AF_UNIX;
> -  len = strlen (path) + 1;
> -  memcpy (addr.sun_path, path, len);
> -  len += sizeof (addr.sun_family);
> -
>     __bind (sock, (struct sockaddr *) &addr, len);
>   
>     if (__getsockname (sock, (struct sockaddr *) &addr, &len) != 0
> diff --git a/sunrpc/tst-bug28768.c b/sunrpc/tst-bug28768.c
> new file mode 100644
> index 0000000000..35a4b7b0b3
> --- /dev/null
> +++ b/sunrpc/tst-bug28768.c
> @@ -0,0 +1,42 @@
> +/* Test to verify that long path is rejected by svcunix_create (bug 28768).
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <rpc/svc.h>
> +#include <shlib-compat.h>
> +#include <string.h>
> +#include <support/check.h>
> +
> +/* svcunix_create does not have a default version in linkobj/libc.so.  */
> +compat_symbol_reference (libc, svcunix_create, svcunix_create, GLIBC_2_1);
> +
> +static int
> +do_test (void)
> +{
> +  char pathname[109];
> +  memset (pathname, 'x', sizeof (pathname));
> +  pathname[sizeof (pathname) - 1] = '\0';
> +
> +  errno = 0;
> +  TEST_VERIFY (svcunix_create (RPC_ANYSOCK, 4096, 4096, pathname) == NULL);
> +  TEST_COMPARE (errno, EINVAL);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>