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Scope reduction to enable NULL check to protect dereferencing. #3312

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merged 2 commits into from
May 11, 2020
Merged

Scope reduction to enable NULL check to protect dereferencing. #3312

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b8aa207
Scope reduction to enable NULL check to protect dereferencing.
sander-visser May 6, 2020
c64b723
Add Changelog entry for #3312
sander-visser May 7, 2020
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3 changes: 3 additions & 0 deletions ChangeLog.d/fix-null-ptr-deref-in-mbedtls_ssl_free.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Bugfix
* Avoid NULL pointer dereferencing if mbedtls_ssl_free() is called with a
NULL pointer argument. Contributed by Sander Visser in #3312.
20 changes: 12 additions & 8 deletions library/ssl_tls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6661,28 +6661,32 @@ int mbedtls_ssl_context_load( mbedtls_ssl_context *context,
*/
void mbedtls_ssl_free( mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
size_t in_buf_len = ssl->in_buf_len;
size_t out_buf_len = ssl->out_buf_len;
#else
size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
#endif

if( ssl == NULL )
return;

MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> free" ) );

if( ssl->out_buf != NULL )
{
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
size_t out_buf_len = ssl->out_buf_len;
#else
size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
#endif

mbedtls_platform_zeroize( ssl->out_buf, out_buf_len );
mbedtls_free( ssl->out_buf );
ssl->out_buf = NULL;
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The whole ssl record is unconditionally zeroed at the end of the function.
This assignment could be removed.

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Indeed. And removing the assignment would also make things more consistent the other allocated structures (transform, session, etc) that we don't explicitly clear.

However IMO this is quite orthogonal to the goal of this PR, so should probably go in a separate PR.

}

if( ssl->in_buf != NULL )
{
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
size_t in_buf_len = ssl->in_buf_len;
#else
size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
#endif

mbedtls_platform_zeroize( ssl->in_buf, in_buf_len );
mbedtls_free( ssl->in_buf );
ssl->in_buf = NULL;
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This assignment could be removed as well.

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