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[tls] Treat invalid block padding as zero length padding
Harden against padding oracle attacks by treating invalid block padding as zero length padding, thereby deferring the failure until after computing the (incorrect) MAC. Signed-off-by: Michael Brown <mcb30@ipxe.org>
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@@ -2821,8 +2821,8 @@ static int tls_new_ciphertext ( struct tls_connection *tls,
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if ( is_block_cipher ( cipher ) ) {
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pad_len = tls_verify_padding ( tls, last );
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if ( pad_len < 0 ) {
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rc = pad_len;
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return rc;
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/* Assume zero padding length to avoid timing attacks */
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pad_len = 0;
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}
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iob_unput ( last, pad_len );
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len -= pad_len;
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