diff options
| author | Daniel Borkmann <dborkman@redhat.com> | 2014-08-26 23:16:35 -0400 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2014-12-14 16:23:49 +0000 |
| commit | 2bdb21fe06c81e977e2bcf1ad3063ba96db9563f (patch) | |
| tree | 0dbabf22202517c4a15db4814223314ab4355e39 | |
| parent | ce2584379f31cfc44bbe770bb78430950a24156e (diff) | |
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>
[bwh: Backported to 3.2:
- extract_buf() needs to use this for the 'extract' array as well
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | drivers/char/random.c | 10 | ||||
| -rw-r--r-- | include/linux/string.h | 2 | ||||
| -rw-r--r-- | lib/string.c | 16 |
3 files changed, 23 insertions, 5 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index c244f0ed61d6..edf45ae694a1 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -954,8 +954,8 @@ 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 @@ -978,7 +978,7 @@ 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, @@ -1010,7 +1010,7 @@ 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; } @@ -1047,7 +1047,7 @@ 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 e033564f10ba..8515a4dbc1c9 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -144,5 +144,7 @@ static inline bool strstarts(const char *str, const char *prefix) { return strncmp(str, prefix, strlen(prefix)) == 0; } + +void memzero_explicit(void *s, size_t count); #endif #endif /* _LINUX_STRING_H_ */ diff --git a/lib/string.c b/lib/string.c index dc4a86341f91..40136f6f8ea3 100644 --- a/lib/string.c +++ b/lib/string.c @@ -583,6 +583,22 @@ 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 |