Fix rpcgen buffer overrun (bug 20790)

Fix rpcgen buffer overrun (bug 20790)

[Joseph Myers]

Building with GCC 7 produces an error building rpcgen:

rpc_parse.c: In function 'get_prog_declaration':
rpc_parse.c:543:25: error: may write a terminating nul past the end of the destination [-Werror=format-length=]
     sprintf (name, "%s%d", ARGNAME, num); /* default name of argument */
                     ~~~~^
rpc_parse.c:543:5: note: format output between 5 and 14 bytes into a destination of size 10
     sprintf (name, "%s%d", ARGNAME, num); /* default name of argument */
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That buffer overrun is for the case where the .x file declares a
program with a million arguments.  The strcpy two lines above can
generate a buffer overrun much more simply for a long argument name.

The limit on length of line read by rpcgen (MAXLINESIZE == 1024)
provides a bound on the buffer size needed, so this patch just changes
the buffer size to MAXLINESIZE to avoid both possible buffer
overruns.  A testcase is added that rpcgen does not crash with a
500-character argument name, where it previously crashed.

It would not at all surprise me if there are many other ways of
crashing rpcgen with either valid or invalid input; fuzz testing would
likely find various such bugs, though I don't think they are that
important to fix (rpcgen is not that likely to be used with untrusted
.x files as input).  (As well as fuzz-findable bugs there are probably
also issues when various int variables get overflowed on very large
input.)  The test infrastructure for rpcgen-not-crashing tests would
need extending if tests are to be added for cases where rpcgen should
produce an error, as opposed to cases where it should succeed.

Tested for x86_64 and x86.

2016-11-07  Joseph Myers  <joseph@codesourcery.com>

	[BZ #20790]
	* sunrpc/rpc_parse.c (get_prog_declaration): Increase buffer size
	to MAXLINESIZE.
	* sunrpc/bug20790.x: New file.
	* sunrpc/Makefile [$(run-built-tests) = yes] (rpcgen-tests): New
	variable.
	[$(run-built-tests) = yes] (tests-special): Add $(rpcgen-tests).
	[$(run-built-tests) = yes] ($(rpcgen-tests)): New rule.

diff --git a/sunrpc/Makefile b/sunrpc/Makefile
index 789ef42..99e5c3c 100644
--- a/sunrpc/Makefile
+++ b/sunrpc/Makefile
@@ -103,6 +103,11 @@ ifeq ($(have-thread-library),yes)
 xtests += thrsvc
 endif
 
+ifeq ($(run-built-tests),yes)
+rpcgen-tests := $(objpfx)bug20790.out
+tests-special += $(rpcgen-tests)
+endif
+
 headers += $(rpcsvc:%.x=rpcsvc/%.h)
 extra-libs := librpcsvc
 extra-libs-others := librpcsvc # Make it in `others' pass, not `lib' pass.
@@ -225,3 +230,9 @@ endif
 endif
 
 $(objpfx)thrsvc: $(common-objpfx)linkobj/libc.so $(shared-thread-library)
+
+ifeq ($(run-built-tests),yes)
+$(rpcgen-tests): $(objpfx)%.out: %.x $(objpfx)rpcgen
+	$(built-program-cmd) -c $< -o $@; \
+	$(evaluate-test)
+endif
diff --git a/sunrpc/bug20790.x b/sunrpc/bug20790.x
new file mode 100644
index 0000000..a00c9b3
--- /dev/null
+++ b/sunrpc/bug20790.x
@@ -0,0 +1 @@
+program TPROG { version TVERS { int FUNC(int aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) = 1; } = 1; } = 1;
diff --git a/sunrpc/rpc_parse.c b/sunrpc/rpc_parse.c
index 1a1df6d..505a655 100644
--- a/sunrpc/rpc_parse.c
+++ b/sunrpc/rpc_parse.c
@@ -521,7 +521,7 @@ static void
 get_prog_declaration (declaration * dec, defkind dkind, int num /* arg number */ )
 {
   token tok;
-  char name[10];		/* argument name */
+  char name[MAXLINESIZE];		/* argument name */
 
   if (dkind == DEF_PROGRAM)
     {

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: Fix rpcgen buffer overrun (bug 20790)

[Florian Weimer]

On 11/07/2016 07:40 PM, Joseph Myers wrote:
> 2016-11-07  Joseph Myers  <joseph@codesourcery.com>
>
> 	[BZ #20790]
> 	* sunrpc/rpc_parse.c (get_prog_declaration): Increase buffer size
> 	to MAXLINESIZE.
> 	* sunrpc/bug20790.x: New file.
> 	* sunrpc/Makefile [$(run-built-tests) = yes] (rpcgen-tests): New
> 	variable.
> 	[$(run-built-tests) = yes] (tests-special): Add $(rpcgen-tests).
> 	[$(run-built-tests) = yes] ($(rpcgen-tests)): New rule.

This looks okay to me, all things considering.  (Fixed-length buffers 
are against GNU coding standards, but sunrpc/* doesn't really follow 
them anyway.)

Thanks,
Florian