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hkdf_expand: explicitly initialize t

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t is never used uninitialized, since the first loop iteration reads 0
bytes of it and then writes hash_len bytes, and subsequent iterations
read and write hash_len bytes. However this is somewhat fragile, and
it would be legitimate for a static analyzer to be unsure.

Initialize t explicitly, to make the code clearer and more robust, at
negligible cost.

Reported by Vasily Evseenko in
https://github.com/ARMmbed/mbedtls/pull/2942
with a slightly different fix.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2020-04-02 19:51:05 +02:00
parent 60d6516c60
commit 3ab121a603
1 changed files with 2 additions and 0 deletions
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library/hkdf.c
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@ -136,6 +136,8 @@ int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
goto exit; goto exit;
} }
memset( t, 0, hash_len );
/* /*
* Compute T = T(1) | T(2) | T(3) | ... | T(N) * Compute T = T(1) | T(2) | T(3) | ... | T(N)
* Where T(N) is defined in RFC 5869 Section 2.3 * Where T(N) is defined in RFC 5869 Section 2.3