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Guard against PSA generating invalid signature

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The goal is not to double-check everything PSA does, but to ensure that it
anything goes wrong, we fail cleanly rather than by overwriting a buffer.
This commit is contained in:
Manuel Pégourié-Gonnard 2018-11-16 10:54:54 +01:00 committed by Hanno Becker
parent f4427678ae
commit 29a1325b0d
1 changed files with 7 additions and 2 deletions
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9
library/pk_wrap.c
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@ -784,13 +784,18 @@ static int asn1_write_mpibuf( unsigned char **p, unsigned char *start,
memmove( *p, start, len ); memmove( *p, start, len );
/* ASN.1 DER encoding requires minimal length, so skip leading 0s. /* ASN.1 DER encoding requires minimal length, so skip leading 0s.
* Neither r nor s can be 0, so we can assume len > 0 at all times. */ * Neither r nor s should be 0, but as a failsafe measure, still detect
while( **p == 0x00 ) * that rather than overflowing the buffer in case of a PSA error. */
while( len > 0 && **p == 0x00 )
{ {
++(*p); ++(*p);
--len; --len;
} }
/* this is only reached if the signature was invalid */
if( len == 0 )
return( MBEDTLS_ERR_PK_HW_ACCEL_FAILED );
/* if the msb is 1, ASN.1 requires that we prepend a 0. /* if the msb is 1, ASN.1 requires that we prepend a 0.
* Neither r nor s can be 0, so we can assume len > 0 at all times. */ * Neither r nor s can be 0, so we can assume len > 0 at all times. */
if( **p & 0x80 ) if( **p & 0x80 )