Fix signature algorithms list entry getting overwritten by length.
Fix bug whereby the supported signature algorithm list sent by the
server in the certificate request would not leave enough space for the
length to be written, and thus the first element would get overwritten,
leaving two random bytes in the last entry.
Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/ChangeLog.d/fix-tls12server-sent-sigalgs.txt b/ChangeLog.d/fix-tls12server-sent-sigalgs.txt
new file mode 100644
index 0000000..9abde2b
--- /dev/null
+++ b/ChangeLog.d/fix-tls12server-sent-sigalgs.txt
@@ -0,0 +1,5 @@
+Bugfix
+ * Fix a bug whereby the the list of signature algorithms sent as part of the
+ TLS 1.2 server certificate request would get corrupted, meaning the first
+ algorithm would not get sent and an entry consisting of two random bytes
+ would be sent instead. Found by Serban Bejan and Dudek Sebastian.
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index 71f703c..3dab246 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -2531,10 +2531,15 @@
if( ! mbedtls_ssl_sig_alg_is_supported( ssl, *sig_alg ) )
continue;
- MBEDTLS_PUT_UINT16_BE( *sig_alg, p, sa_len );
+ /* Write elements at offsets starting from 1 (offset 0 is for the
+ * length). Thus the offset of each element is the length of the
+ * partial list including that element. */
sa_len += 2;
+ MBEDTLS_PUT_UINT16_BE( *sig_alg, p, sa_len );
+
}
+ /* Fill in list length. */
MBEDTLS_PUT_UINT16_BE( sa_len, p, 0 );
sa_len += 2;
p += sa_len;