dropbear: bump to 2017.75

- Security: Fix double-free in server TCP listener cleanup A double-free
in the server could be triggered by an authenticated user if dropbear is
running with -a (Allow connections to forwarded ports from any host)
This could potentially allow arbitrary code execution as root by an
authenticated user.  Affects versions 2013.56 to 2016.74. Thanks to Mark
Shepard for reporting the crash.
CVE-2017-9078 https://secure.ucc.asn.au/hg/dropbear/rev/c8114a48837c

- Security: Fix information disclosure with ~/.ssh/authorized_keys
symlink.  Dropbear parsed authorized_keys as root, even if it were a
symlink.  The fix is to switch to user permissions when opening
authorized_keys

A user could symlink their ~/.ssh/authorized_keys to a root-owned file
they couldn't normally read. If they managed to get that file to contain
valid authorized_keys with command= options it might be possible to read
other contents of that file.
This information disclosure is to an already authenticated user.
Thanks to Jann Horn of Google Project Zero for reporting this.
CVE-2017-9079 https://secure.ucc.asn.au/hg/dropbear/rev/0d889b068123

Refresh patches, rework 100-pubkey_path.patch to work with new
authorized_keys validation.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>

package/network/services/dropbear/Makefile

@@ -8,14 +8,14 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=dropbear
-PKG_VERSION:=2016.74
-PKG_RELEASE:=2
+PKG_VERSION:=2017.75
+PKG_RELEASE:=1
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:= \
 	http://matt.ucc.asn.au/dropbear/releases/ \
 	https://dropbear.nl/mirror/releases/
-PKG_HASH:=2720ea54ed009af812701bcc290a2a601d5c107d12993e5d92c0f5f81f718891
+PKG_HASH:=6cbc1dcb1c9709d226dff669e5604172a18cf5dbf9a201474d5618ae4465098c
 
 PKG_LICENSE:=MIT
 PKG_LICENSE_FILES:=LICENSE libtomcrypt/LICENSE libtommath/LICENSE

package/network/services/dropbear/patches/100-pubkey_path.patch

@@ -1,6 +1,6 @@
 --- a/svr-authpubkey.c
 +++ b/svr-authpubkey.c
-@@ -218,17 +218,21 @@ static int checkpubkey(char* algo, unsig
+@@ -220,14 +220,20 @@ static int checkpubkey(char* algo, unsig
  		goto out;
  	}
  
@@ -12,9 +12,6 @@
 -	filename = m_malloc(len + 22);
 -	snprintf(filename, len + 22, "%s/.ssh/authorized_keys", 
 -				ses.authstate.pw_dir);
--
--	/* open the file */
--	authfile = fopen(filename, "r");
 +	if (ses.authstate.pw_uid != 0) {
 +		/* we don't need to check pw and pw_dir for validity, since
 +		 * its been done in checkpubkeyperms. */
@@ -22,18 +19,17 @@
 +		/* allocate max required pathname storage,
 +		 * = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
 +		filename = m_malloc(len + 22);
-+		snprintf(filename, len + 22, "%s/.ssh/authorized_keys", 
-+		         ses.authstate.pw_dir);
-+
-+		/* open the file */
-+		authfile = fopen(filename, "r");
++		snprintf(filename, len + 22, "%s/.ssh/authorized_keys",
++					ses.authstate.pw_dir);
 +	} else {
-+		authfile = fopen("/etc/dropbear/authorized_keys","r");
++		filename = m_malloc(30);
++		strncpy(filename, "/etc/dropbear/authorized_keys", 30);
 +	}
- 	if (authfile == NULL) {
- 		goto out;
- 	}
-@@ -381,26 +385,35 @@ static int checkpubkeyperms() {
++
+ 
+ 	/* open the file as the authenticating user. */
+ 	origuid = getuid();
+@@ -396,26 +402,35 @@ static int checkpubkeyperms() {
  		goto out;
  	}