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[RFC] Warning for potentially unbound writes to function parameters
- From: Florian Weimer <fweimer at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 17 Aug 2012 18:22:22 +0200
- Subject: [RFC] Warning for potentially unbound writes to function parameters
In some real-world code, I noticed a curious pattern: using the unsafe
string functions on function parameter arguments. This leads to
gets()-style unsafe APIs.
I've looked at how to implement a warning for this, and came up with the
attached patch. Do you think this makes sense?
1 #include <string.h>
2
3 const char *data (void);
4
5 void test (char *target)
6 {
7 strcpy(target, data ());
8 }
9
10
11 void test_2 (char *target)
12 {
13 char *p = target;
14 strcpy(p, data ());
15 }
16
/tmp/t.c: In function ‘test’:
/tmp/t.c:7:9: warning: potentially unbound write to function parameter
‘target’ [-Wunbound-parameter-write]
strcpy(target, data ());
^
/tmp/t.c: In function ‘test_2’:
/tmp/t.c:14:9: warning: potentially unbound write to function parameter
‘target’ [-Wunbound-parameter-write]
strcpy(p, data ());
^
Obviously, the warning and its name need adjusting, and more functions
need to be covered. But I want to check first if you think the warning
makes sense at all, and if I've found the right place to implement it
(this approach seems to require optimization, alas).
--
Florian Weimer / Red Hat Product Security Team
commit 324c7189c9cf871584da988f12d1a686df0d6e0c
Author: Florian Weimer <fweimer@redhat.com>
Date: Fri Aug 17 18:19:13 2012 +0200
Implement -Wunbound-parameter-write (proof of concept)
diff --git a/gcc/builtins.c b/gcc/builtins.c
index 4b177c4..dc90484 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -3274,6 +3274,14 @@ expand_builtin_strcpy (tree exp, rtx target)
{
tree dest = CALL_EXPR_ARG (exp, 0);
tree src = CALL_EXPR_ARG (exp, 1);
+ if (TREE_CODE (dest) == SSA_NAME)
+ {
+ tree dest_var = SSA_NAME_VAR (dest);
+ if (TREE_CODE (dest_var) == PARM_DECL)
+ warning_at (EXPR_LOCATION (exp), OPT_Wunbound_parameter_write,
+ "potentially unbound write to function parameter %qD",
+ dest_var);
+ }
return expand_builtin_strcpy_args (dest, src, target);
}
return NULL_RTX;
diff --git a/gcc/common.opt b/gcc/common.opt
index deb89e3..fe892b7 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -562,6 +562,10 @@ Wlarger-than=
Common RejectNegative Joined UInteger Warning
-Wlarger-than=<number> Warn if an object is larger than <number> bytes
+Wunbound-parameter-write
+Common Var(warn_unbound_parameter_write) Warning
+Warn if a function without array bounds checking writes to a pointer passed as an parameter
+
Wunsafe-loop-optimizations
Common Var(warn_unsafe_loop_optimizations) Warning
Warn if the loop cannot be optimized due to nontrivial assumptions.