pki: Add a size limit for pubkey files.

include/libssh/pki.h

@@ -31,6 +31,8 @@
 
 #include "libssh/crypto.h"
 
+#define MAX_PUBKEY_SIZE 0x100000 /* 1M */
+
 #define SSH_KEY_FLAG_EMPTY   0x0
 #define SSH_KEY_FLAG_PUBLIC  0x0001
 #define SSH_KEY_FLAG_PRIVATE 0x0002

src/pki.c

@@ -816,7 +816,7 @@ int ssh_pki_import_pubkey_file(const char *filename, ssh_key *pkey)
         return SSH_ERROR;
     }
 
-    if (sb.st_size + 1 < sb.st_size) {
+    if (sb.st_size > MAX_PUBKEY_SIZE) {
         return SSH_ERROR;
     }