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Make entropy double-free work

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Although the library documentation does not guarantee that calling
mbedtls_entropy_free() twice works, it's a plausible assumption and it's
natural to write code that frees an object twice. While this is uncommon for
an entropy context, which is usually a global variable, it came up in our
own unit tests (random_twice tests in test_suite_random).

Announce this in the same changelog entry as for RSA because it's the same
bug in the two modules.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-02-22 21:26:54 +01:00
parent 3d979f781e
commit b15832160b
3 changed files with 14 additions and 7 deletions
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7
library/entropy.c
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@ -116,6 +116,11 @@ void mbedtls_entropy_init( mbedtls_entropy_context *ctx )
void mbedtls_entropy_free( mbedtls_entropy_context *ctx )
{
/* If the context was already free, don't call free() again.
* This is important for mutexes which don't allow double-free. */
if( ctx->accumulator_started == -1 )
return;
#if defined(MBEDTLS_HAVEGE_C)
mbedtls_havege_free( &ctx->havege_data );
#endif
@ -132,7 +137,7 @@ void mbedtls_entropy_free( mbedtls_entropy_context *ctx )
#endif
ctx->source_count = 0;
mbedtls_platform_zeroize( ctx->source, sizeof( ctx->source ) );
ctx->accumulator_started = 0;
ctx->accumulator_started = -1;
}
int mbedtls_entropy_add_source( mbedtls_entropy_context *ctx,