From: Matt Caswell <matt@openssl.org>
Date: Wed, 12 Oct 2016 15:43:03 +0000 (+0100)
Subject: Ensure we handle len == 0 in ERR_err_string_n
X-Git-Tag: OpenSSL_1_1_0c~84
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=953ef2cbd0645a47b8d5c1af3fe8f77f2e56c133;p=oweals%2Fopenssl.git

Ensure we handle len == 0 in ERR_err_string_n

If len == 0 in a call to ERR_error_string_n() then we can read beyond the
end of the buffer. Really applications should not be calling this function
with len == 0, but we shouldn't be letting it through either!

Thanks to Agostino Sarubbo for reporting this issue. Agostino's blog on
this issue is available here:
https://blogs.gentoo.org/ago/2016/10/14/openssl-libcrypto-stack-based-buffer-overflow-in-err_error_string_n-err-c/

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit e5c1361580d8de79682958b04a5f0d262e680f8b)
---

diff --git a/crypto/err/err.c b/crypto/err/err.c
index c3f7212a78..29e5a03197 100644
--- a/crypto/err/err.c
+++ b/crypto/err/err.c
@@ -500,6 +500,9 @@ void ERR_error_string_n(unsigned long e, char *buf, size_t len)
     const char *ls, *fs, *rs;
     unsigned long l, f, r;
 
+    if (len == 0)
+        return;
+
     l = ERR_GET_LIB(e);
     f = ERR_GET_FUNC(e);
     r = ERR_GET_REASON(e);