[3.16.y-ckt extended stable] Patch "random: add and use memzero_explicit() for clearing data" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    random: add and use memzero_explicit() for clearing data

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From eb622aa247403320d572f652e6807d2e926c3b39 Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <dborkman at redhat.com>
Date: Tue, 26 Aug 2014 23:16:35 -0400
Subject: 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 at hotmail.co.uk
Signed-off-by: Daniel Borkmann <dborkman at redhat.com>
Acked-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan at gmail.com>
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
[ kamal: backport to 3.13-stable: one more memzero_explicit in extract_buf() ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/char/random.c  | 10 +++++-----
 include/linux/string.h |  5 +++--
 lib/string.c           | 16 ++++++++++++++++
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 71529e196b84..dde8da31dcae 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1076,8 +1076,8 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
 	 * pool while mixing, and hash one final time.
 	 */
 	sha_transform(hash.w, extract, workspace);
-	memset(extract, 0, sizeof(extract));
-	memset(workspace, 0, sizeof(workspace));
+	memzero_explicit(extract, sizeof(extract));
+	memzero_explicit(workspace, sizeof(workspace));

 	/*
 	 * In case the hash function has some recognizable output
@@ -1089,7 +1089,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
 	hash.w[2] ^= rol32(hash.w[2], 16);

 	memcpy(out, &hash, EXTRACT_SIZE);
-	memset(&hash, 0, sizeof(hash));
+	memzero_explicit(&hash, sizeof(hash));
 }

 /*
@@ -1146,7 +1146,7 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
 	}

 	/* Wipe data just returned from memory */
-	memset(tmp, 0, sizeof(tmp));
+	memzero_explicit(tmp, sizeof(tmp));

 	return ret;
 }
@@ -1188,7 +1188,7 @@ static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
 	}

 	/* Wipe data just returned from memory */
-	memset(tmp, 0, sizeof(tmp));
+	memzero_explicit(tmp, sizeof(tmp));

 	return ret;
 }
diff --git a/include/linux/string.h b/include/linux/string.h
index d36977e029af..3b42b3732da6 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -132,7 +132,7 @@ int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
 #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?
@@ -144,7 +144,8 @@ static inline bool strstarts(const char *str, const char *prefix)
 	return strncmp(str, prefix, strlen(prefix)) == 0;
 }

-extern size_t memweight(const void *ptr, size_t bytes);
+size_t memweight(const void *ptr, size_t bytes);
+void memzero_explicit(void *s, size_t count);

 /**
  * kbasename - return the last part of a pathname.
diff --git a/lib/string.c b/lib/string.c
index 992bf30af759..3a3120452a1d 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -604,6 +604,22 @@ void *memset(void *s, int c, size_t count)
 EXPORT_SYMBOL(memset);
 #endif

+/**
+ * memzero_explicit - Fill a region of memory (e.g. sensitive
+ *		      keying data) with 0s.
+ * @s: Pointer to the start of the area.
+ * @count: The size of the area.
+ *
+ * memzero_explicit() doesn't need an arch-specific version as
+ * it just invokes the one of memset() implicitly.
+ */
+void memzero_explicit(void *s, size_t count)
+{
+	memset(s, 0, count);
+	OPTIMIZER_HIDE_VAR(s);
+}
+EXPORT_SYMBOL(memzero_explicit);
+
 #ifndef __HAVE_ARCH_MEMCPY
 /**
  * memcpy - Copy one area of memory to another
--
2.1.0