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Message-Id: <1491513513-84351-9-git-send-email-keescook@chromium.org>
Date: Thu, 6 Apr 2017 14:18:23 -0700
From: Kees Cook <keescook@...omium.org>
To: kernel-hardening@...ts.openwall.com
Cc: Kees Cook <keescook@...omium.org>,
Michael Leibowitz <michael.leibowitz@...el.com>
Subject: [PATCH 08/18] randstruct: Whitelist UNIXCB cast
This is another false positive in bad cast detection:
net/unix/af_unix.c: In function ‘unix_skb_scm_eq’:
net/unix/af_unix.c:1621:31: note: found mismatched rhs struct pointer types: ‘struct unix_skb_parms’ and ‘char’
const struct unix_skb_parms *u = &UNIXCB(skb);
^
UNIXCB is:
#define UNIXCB(skb) (*(struct unix_skb_parms *)&((skb)->cb))
And ->cb is:
char cb[48] __aligned(8);
This is a rather crazy cast, but appears to be safe in the face of
randomization, so whitelist it in the plugin.
Signed-off-by: Kees Cook <keescook@...omium.org>
---
scripts/gcc-plugins/randomize_layout_plugin.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index 63c654a00249..a2d7e933c33f 100644
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -773,6 +773,15 @@ static bool type_name_eq(gimple stmt, const_tree type_tree, const char *wanted_n
case RECORD_TYPE:
type_name = TYPE_NAME_POINTER(type_tree);
break;
+ case INTEGER_TYPE:
+ if (TYPE_PRECISION(type_tree) == CHAR_TYPE_SIZE)
+ type_name = "char";
+ else {
+ inform(gimple_location(stmt), "found non-char INTEGER_TYPE cast comparison: %qT\n", type_tree);
+ debug_tree(type_tree);
+ return false;
+ }
+ break;
default:
inform(gimple_location(stmt), "unhandled cast comparison: %qT\n", type_tree);
debug_tree(type_tree);
@@ -864,7 +873,13 @@ static unsigned int find_bad_casts_execute(void)
#ifndef __DEBUG_PLUGIN
if (lookup_attribute("randomize_performed", TYPE_ATTRIBUTES(ptr_lhs_type)))
#endif
- inform(gimple_location(stmt), "found mismatched rhs struct pointer types: %qT and %qT\n", ptr_lhs_type, ptr_rhs_type);
+ {
+ /* Whitelist unix_skb_parms via UNIXCB() */
+ if (whitelisted_cast(stmt, ptr_lhs_type, ptr_rhs_type, "unix_skb_parms", "char"))
+ continue;
+
+ inform(gimple_location(stmt), "found mismatched rhs struct pointer types: %qT and %qT\n", ptr_lhs_type, ptr_rhs_type);
+ }
continue;
}
--
2.7.4
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