From 3b29acb38f39aea8cf7675eadd5214300149bb9e Mon Sep 17 00:00:00 2001 From: Daniel Borkmann 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@hotmail.co.uk Signed-off-by: Daniel Borkmann Acked-by: Hannes Frederic Sowa Cc: Alexey Dobriyan Signed-off-by: Theodore Ts'o Signed-off-by: Jiri Slaby --- drivers/char/random.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'drivers/char') diff --git a/drivers/char/random.c b/drivers/char/random.c index 7a744d391756..f6b25db16791 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -930,8 +930,8 @@ 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 @@ -954,7 +954,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out) } memcpy(out, &hash, EXTRACT_SIZE); - memset(&hash, 0, sizeof(hash)); + memzero_explicit(&hash, sizeof(hash)); } static ssize_t extract_entropy(struct entropy_store *r, void *buf, @@ -1002,7 +1002,7 @@ 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; } @@ -1040,7 +1040,7 @@ 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; } -- cgit v1.2.3