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Commit d4c5efdb authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Theodore Ts'o
Browse files

random: add and use memzero_explicit() for clearing data 



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: default avatar <zatimend@hotmail.co.uk>
Signed-off-by: default avatarDaniel Borkmann <dborkman@redhat.com>
Acked-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
parent 7d1311b9

drivers/char/random.c

+4 −4
Original line number Original line Diff line number Diff line
@@ -1106,7 +1106,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out) 
	__mix_pool_bytes(r, hash.w, sizeof(hash.w));

	__mix_pool_bytes(r, hash.w, sizeof(hash.w));

	spin_unlock_irqrestore(&r->lock, flags);

	spin_unlock_irqrestore(&r->lock, flags);





	memset(workspace, 0, sizeof(workspace));

	memzero_explicit(workspace, sizeof(workspace));





	/*

	/*

	 * In case the hash function has some recognizable output

	 * In case the hash function has some recognizable output
@@ -1118,7 +1118,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out) 
	hash.w[2] ^= rol32(hash.w[2], 16);

	hash.w[2] ^= rol32(hash.w[2], 16);





	memcpy(out, &hash, EXTRACT_SIZE);

	memcpy(out, &hash, EXTRACT_SIZE);

	memset(&hash, 0, sizeof(hash));

	memzero_explicit(&hash, sizeof(hash));

}

}





/*

/*
@@ -1175,7 +1175,7 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf, 
	}

	}





	/* Wipe data just returned from memory */

	/* Wipe data just returned from memory */

	memset(tmp, 0, sizeof(tmp));

	memzero_explicit(tmp, sizeof(tmp));





	return ret;

	return ret;

}

}
@@ -1218,7 +1218,7 @@ static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf, 
	}

	}





	/* Wipe data just returned from memory */

	/* Wipe data just returned from memory */

	memset(tmp, 0, sizeof(tmp));

	memzero_explicit(tmp, sizeof(tmp));





	return ret;

	return ret;

}

}

include/linux/string.h

+3 −2
Original line number Original line Diff line number Diff line
@@ -144,7 +144,8 @@ static inline bool strstarts(const char *str, const char *prefix) 
	return strncmp(str, prefix, strlen(prefix)) == 0;

	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.

 * kbasename - return the last part of a pathname.

lib/string.c

+16 −0
Original line number Original line Diff line number Diff line
@@ -604,6 +604,22 @@ void *memset(void *s, int c, size_t count) 
EXPORT_SYMBOL(memset);

EXPORT_SYMBOL(memset);

#endif

#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

#ifndef __HAVE_ARCH_MEMCPY

/**

/**

 * memcpy - Copy one area of memory to another

 * memcpy - Copy one area of memory to another