From d070b4ae78a1280c5cb6b88df75bcbfbcef6a8f1 Mon Sep 17 00:00:00 2001
From: "Dr. Matthias St. Pierre" <Matthias.St.Pierre@ncp-e.com>
Date: Wed, 21 Feb 2018 01:45:14 +0100
Subject: [PATCH] bio_b64.c: prevent base64 filter BIO from decoding
out-of-bound data
Fixes #5405, #1381
The base64 filter BIO reads its input in chunks of B64_BLOCK_SIZE bytes.
When processing input in PEM format it can happen in rare cases that
- the trailing PEM marker crosses the boundary of a chunk, and
- the beginning of the following chunk contains valid base64 encoded data.
This happened in issue #5405, where the PEM marker was split into
"-----END CER" and "TIFICATE-----" at the end of the first chunk.
The decoding of the first chunk terminated correctly at the '-' character,
which is treated as an EOF marker, and b64_read() returned. However,
when called the second time, b64_read() read the next chunk and interpreted
the string "TIFICATE" as valid base64 encoded data, adding 6 extra bytes
'4c 81 48 08 04 c4'.
This patch restores the assignment of the error code to 'ctx->cont', which
was deleted accidentally in commit 5562cfaca4f3 and which prevents b64_read()
from reading additional data on subsequent calls.
This issue was observed and reported by Annie Yousar.
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5422)
---
crypto/evp/bio_b64.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/crypto/evp/bio_b64.c b/crypto/evp/bio_b64.c
index cade6f8f95..e70fc322d8 100644
--- a/crypto/evp/bio_b64.c
+++ b/crypto/evp/bio_b64.c
@@ -289,6 +289,14 @@ static int b64_read(BIO *b, char *out, int outl)
(unsigned char *)ctx->tmp, i);
ctx->tmp_len = 0;
}
+ /*
+ * If eof or an error was signalled, then the condition
+ * 'ctx->cont <= 0' will prevent b64_read() from reading
+ * more data on subsequent calls. This assignment was
+ * deleted accidentally in commit 5562cfaca4f3.
+ */
+ ctx->cont = i;
+
ctx->buf_off = 0;
if (i < 0) {
ret_code = 0;
--
2.25.1