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RSA decrypt: don't write past buffer end on error #9454

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Merged
merged 1 commit into from
Dec 4, 2025
+27 −6
Merged

RSA decrypt: don't write past buffer end on error #9454

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8 changes: 8 additions & 0 deletions tests/api/test_rsa.c
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Original file line number Diff line number Diff line change
Expand Up @@ -789,15 +789,18 @@ int test_wc_RsaPublicEncryptDecrypt(void)
WC_DECLARE_VAR(in, byte, TEST_STRING_SZ, NULL);
WC_DECLARE_VAR(plain, byte, TEST_STRING_SZ, NULL);
WC_DECLARE_VAR(cipher, byte, TEST_RSA_BYTES, NULL);
WC_DECLARE_VAR(shortPlain, byte, TEST_STRING_SZ - 4, NULL);

WC_ALLOC_VAR(in, byte, TEST_STRING_SZ, NULL);
WC_ALLOC_VAR(plain, byte, TEST_STRING_SZ, NULL);
WC_ALLOC_VAR(cipher, byte, TEST_RSA_BYTES, NULL);
WC_ALLOC_VAR(shortPlain, byte, TEST_STRING_SZ - 4, NULL);

#ifdef WC_DECLARE_VAR_IS_HEAP_ALLOC
ExpectNotNull(in);
ExpectNotNull(plain);
ExpectNotNull(cipher);
ExpectNotNull(shortPlain);
#endif
ExpectNotNull(XMEMCPY(in, inStr, inLen));

Expand All @@ -824,6 +827,11 @@ int test_wc_RsaPublicEncryptDecrypt(void)
ExpectIntEQ(XMEMCMP(plain, inStr, plainLen), 0);
/* Pass bad args - tested in another testing function.*/

/* Test for when plain length is less than required. */
ExpectIntEQ(wc_RsaPrivateDecrypt(cipher, cipherLenResult, shortPlain,
TEST_STRING_SZ - 4, &key), RSA_BUFFER_E);

WC_FREE_VAR(shortPlain, NULL);
WC_FREE_VAR(in, NULL);
WC_FREE_VAR(plain, NULL);
WC_FREE_VAR(cipher, NULL);
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25 changes: 19 additions & 6 deletions wolfcrypt/src/rsa.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3636,15 +3636,28 @@ static int RsaPrivateDecryptEx(const byte* in, word32 inLen, byte* out,
if (rsa_type == RSA_PRIVATE_DECRYPT) {
word32 i = 0;
word32 j;
byte last = 0;
int start = (int)((size_t)pad - (size_t)key->data);

for (j = 0; j < key->dataLen; j++) {
signed char c;
out[i] = key->data[j];
c = (signed char)ctMaskGTE((int)j, start);
c &= (signed char)ctMaskLT((int)i, (int)outLen);
/* 0 - no add, -1 add */
i += (word32)((byte)(-c));
signed char incMask;
signed char maskData;

/* When j < start + outLen then out[i] = key->data[j]
* else out[i] = last
*/
maskData = (signed char)ctMaskLT((int)j,
start + (int)outLen);
out[i] = (byte)(key->data[j] & maskData ) |
(byte)(last & (~maskData));
last = out[i];

/* Increment i when j is in range:
* [start..(start + outLen - 1)]. */
incMask = (signed char)ctMaskGTE((int)j, start);
incMask &= (signed char)ctMaskLT((int)j,
start + (int)outLen - 1);
i += (word32)((byte)(-incMask));
}
}
else
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