linux-kernel - [PATCH] uaccess: Disallow > INT

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Message-ID: <201908251612.F9902D7A@keescook>
Date:   Sun, 25 Aug 2019 16:18:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] uaccess: Disallow > INT_MAX copy sizes

As we've done with VFS, string operations, etc, reject usercopy sizes
larger than INT_MAX, which would be nice to have for catching bugs
related to size calculation overflows[1].

This adds 10 bytes to x86_64 defconfig text and 1980 bytes to the data
section:

   text    data     bss     dec     hex filename
19691167        5134320 1646664 26472151        193eed7 vmlinux.before
19691177        5136300 1646664 26474141        193f69d vmlinux.after

[1] https://marc.info/?l=linux-s390&m=156631939010493&w=2

Suggested-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/thread_info.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 659a4400517b..e93e249a4e9b 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -147,6 +147,8 @@ check_copy_size(const void *addr, size_t bytes, bool is_source)
 			__bad_copy_to();
 		return false;
 	}
+	if (WARN_ON_ONCE(bytes > INT_MAX))
+		return false;
 	check_object_size(addr, bytes, is_source);
 	return true;
 }
-- 
2.17.1


-- 
Kees Cook