random: add and use memzero_explicit() for clearing data
commit d4c5efdb97773f59a2b711754ca0953f24516739 upstream.
zatimend has reported that in his environment (3.16/gcc4.8.3/corei7)
memset() calls which clear out sensitive data in extract_{buf,entropy,
entropy_user}() in random driver are being optimized away by gcc.
Add a helper memzero_explicit() (similarly as explicit_bzero() variants)
that can be used in such cases where a variable with sensitive data is
being cleared out in the end. Other use cases might also be in crypto
code. [ I have put this into lib/string.c though, as it's always built-in
and doesn't need any dependencies then. ]
Fixes kernel bugzilla: 82041
Reported-by: zatimend@hotmail.co.uk
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[lizf: Backported to 3.4:
- adjust context
- another memset() in extract_buf() needs to be converted]
Signed-off-by: Zefan Li <lizefan@huawei.com>
diff --git a/include/linux/string.h b/include/linux/string.h
index e033564..3d9feb7 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -133,7 +133,7 @@
#endif
extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
- const void *from, size_t available);
+ const void *from, size_t available);
/**
* strstarts - does @str start with @prefix?
@@ -144,5 +144,7 @@
{
return strncmp(str, prefix, strlen(prefix)) == 0;
}
+
+void memzero_explicit(void *s, size_t count);
#endif
#endif /* _LINUX_STRING_H_ */