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Fix null pointer arithmetic in error case

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When mbedtls_nist_kw_wrap was called with output=NULL and out_size=0, it
performed arithmetic on the null pointer before detecting that the output
buffer is too small and returning an error code. This was unlikely to have
consequences on real-world hardware today, but it is undefined behavior and
UBSan with Clang 10 flagged it. So fix it (fix #4025).

Fix a similar-looking pattern in unwrap, though I haven't verified that it's
reachable there.

Signed-off-by: Gilles Peskine <[email protected]>
This commit is contained in:
Gilles Peskine
2021-06-01 13:03:34 +02:00
parent 8e7d7ee1ae
commit 995d89c9f2
1 changed files with 5 additions and 3 deletions
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library/nist_kw.c
+5 -3
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@@ -219,8 +219,6 @@ int mbedtls_nist_kw_wrap( mbedtls_nist_kw_context *ctx,
uint64_t t = 0;
unsigned char outbuff[KW_SEMIBLOCK_LENGTH * 2];
unsigned char inbuff[KW_SEMIBLOCK_LENGTH * 2];
unsigned char *R2 = output + KW_SEMIBLOCK_LENGTH;
unsigned char *A = output;
*out_len = 0;
/*
@@ -296,6 +294,9 @@ int mbedtls_nist_kw_wrap( mbedtls_nist_kw_context *ctx,
}
else
{
unsigned char *R2 = output + KW_SEMIBLOCK_LENGTH;
unsigned char *A = output;
/*
* Do the wrapping function W, as defined in RFC 3394 section 2.2.1
*/
@@ -359,7 +360,7 @@ static int unwrap( mbedtls_nist_kw_context *ctx,
uint64_t t = 0;
unsigned char outbuff[KW_SEMIBLOCK_LENGTH * 2];
unsigned char inbuff[KW_SEMIBLOCK_LENGTH * 2];
unsigned char *R = output + ( semiblocks - 2 ) * KW_SEMIBLOCK_LENGTH;
unsigned char *R = NULL;
*out_len = 0;
if( semiblocks < MIN_SEMIBLOCKS_COUNT )
@@ -369,6 +370,7 @@ static int unwrap( mbedtls_nist_kw_context *ctx,
memcpy( A, input, KW_SEMIBLOCK_LENGTH );
memmove( output, input + KW_SEMIBLOCK_LENGTH, ( semiblocks - 1 ) * KW_SEMIBLOCK_LENGTH );
R = output + ( semiblocks - 2 ) * KW_SEMIBLOCK_LENGTH;
/* Calculate intermediate values */
for( t = s; t >= 1; t-- )