From fa7b23ce9025daba08e86bb934fc430099792b9a Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Tue, 10 Nov 2015 18:47:55 +0000
Subject: [PATCH] Fix a segfault in parsing OpenSSH private key files.
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The initial test for a line ending with "PRIVATE KEY-----" failed to
take into account the possibility that the line might be shorter than
that. Fixed by introducing a new library function strendswith(), and
strstartswith() for good measure, and using that.

Thanks to Hanno Böck for spotting this, with the aid of AFL.
---
 import.c |  8 ++++----
 misc.c   | 11 +++++++++++
 misc.h   |  2 ++
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/import.c b/import.c
index 508ef782..49846a6e 100644
--- a/import.c
+++ b/import.c
@@ -383,8 +383,8 @@ static struct openssh_pem_key *load_openssh_pem_key(const Filename *filename,
 	goto error;
     }
     strip_crlf(line);
-    if (0 != strncmp(line, "-----BEGIN ", 11) ||
-	0 != strcmp(line+strlen(line)-16, "PRIVATE KEY-----")) {
+    if (!strstartswith(line, "-----BEGIN ") ||
+        !strendswith(line, "PRIVATE KEY-----")) {
 	errmsg = "file does not begin with OpenSSH key header";
 	goto error;
     }
@@ -421,8 +421,8 @@ static struct openssh_pem_key *load_openssh_pem_key(const Filename *filename,
 	    goto error;
 	}
 	strip_crlf(line);
-	if (0 == strncmp(line, "-----END ", 9) &&
-	    0 == strcmp(line+strlen(line)-16, "PRIVATE KEY-----")) {
+	if (strstartswith(line, "-----END ") &&
+	    strendswith(line, "PRIVATE KEY-----")) {
             sfree(line);
             line = NULL;
 	    break;		       /* done */
diff --git a/misc.c b/misc.c
index 6af441c3..618ca297 100644
--- a/misc.c
+++ b/misc.c
@@ -1087,3 +1087,14 @@ int get_ssh_uint32(int *datalen, const void **data, unsigned *ret)
     *data = (const char *)*data + 4;
     return TRUE;
 }
+
+int strstartswith(const char *s, const char *t)
+{
+    return !memcmp(s, t, strlen(t));
+}
+
+int strendswith(const char *s, const char *t)
+{
+    size_t slen = strlen(s), tlen = strlen(t);
+    return slen >= tlen && !strcmp(s + (slen - tlen), t);
+}
diff --git a/misc.h b/misc.h
index 8c8377f9..ae33e96e 100644
--- a/misc.h
+++ b/misc.h
@@ -52,6 +52,8 @@ int toint(unsigned);
 
 char *fgetline(FILE *fp);
 char *chomp(char *str);
+int strstartswith(const char *s, const char *t);
+int strendswith(const char *s, const char *t);
 
 void base64_encode_atom(const unsigned char *data, int n, char *out);
 int base64_decode_atom(const char *atom, unsigned char *out);
-- 
2.45.2