* Mitigate OpenSSL security vulnerability:

  - Add key blacklisting support. Keys listed in
    /etc/ssh/blacklist.TYPE-LENGTH will be rejected for authentication by
    sshd, unless "PermitBlacklistedKeys yes" is set in
    /etc/ssh/sshd_config.
  - Add a new program, ssh-vulnkey, which can be used to check keys
    against these blacklists.
  - Depend on openssh-blacklist.
  - Force dependencies on libssl0.9.8 / libcrypto0.9.8-udeb to at least
    0.9.8g-9.
  - Automatically regenerate known-compromised host keys, with a
    critical-priority debconf note. (I regret that there was no time to
    gather translations.)

1 files changed, 111 insertions, 0 deletions

diff --git a/authfile.c b/authfile.c
index 735c64780..5348a014d 100644
--- a/authfile.c
+++ b/authfile.c
@@ -65,6 +65,7 @@
 #include "rsa.h"
 #include "misc.h"
 #include "atomicio.h"
+#include "pathnames.h"
 
 /* Version identification string for SSH v1 identity files. */
 static const char authfile_id_string[] =
@@ -677,3 +678,113 @@ key_load_public(const char *filename, char **commentp)
         key_free(pub);
         return NULL;
 }
+
+char *
+blacklist_filename(const Key *key)
+{
+        char *name;
+
+        xasprintf(&name, "%s.%s-%u",
+            _PATH_BLACKLIST, key_type(key), key_size(key));
+        return name;
+}
+
+/* Scan a blacklist of known-vulnerable keys. */
+int
+blacklisted_key(const Key *key)
+{
+        char *blacklist_file;
+        int fd = -1;
+        char *dgst_hex = NULL;
+        char *dgst_packed = NULL, *p;
+        int i;
+        size_t line_len;
+        struct stat st;
+        char buf[256];
+        off_t start, lower, upper;
+        int ret = 0;
+
+        blacklist_file = blacklist_filename(key);
+        debug("Checking blacklist file %s", blacklist_file);
+        fd = open(blacklist_file, O_RDONLY);
+        if (fd < 0)
+                goto out;
+
+        dgst_hex = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
+        /* Remove all colons */
+        dgst_packed = xcalloc(1, strlen(dgst_hex) + 1);
+        for (i = 0, p = dgst_packed; dgst_hex[i]; i++)
+                if (dgst_hex[i] != ':')
+                        *p++ = dgst_hex[i];
+        /* Only compare least-significant 80 bits (to keep the blacklist
+         * size down)
+         */
+        line_len = strlen(dgst_packed + 12);
+        if (line_len > 32)
+                goto out;
+
+        /* Skip leading comments */
+        start = 0;
+        for (;;) {
+                ssize_t r;
+                char *newline;
+
+                r = atomicio(read, fd, buf, 256);
+                if (r <= 0)
+                        goto out;
+                if (buf[0] != '#')
+                        break;
+
+                newline = memchr(buf, '\n', 256);
+                if (!newline)
+                        goto out;
+                start += newline + 1 - buf;
+                if (lseek(fd, start, SEEK_SET) < 0)
+                        goto out;
+        }
+
+        /* Initialise binary search record numbers */
+        if (fstat(fd, &st) < 0)
+                goto out;
+        lower = 0;
+        upper = (st.st_size - start) / (line_len + 1);
+
+        while (lower != upper) {
+                off_t cur;
+                char buf[32];
+                int cmp;
+
+                cur = lower + (upper - lower) / 2;
+
+                /* Read this line and compare to digest; this is
+                 * overflow-safe since cur < max(off_t) / (line_len + 1) */
+                if (lseek(fd, start + cur * (line_len + 1), SEEK_SET) < 0)
+                        break;
+                if (atomicio(read, fd, buf, line_len) != line_len)
+                        break;
+                cmp = memcmp(buf, dgst_packed + 12, line_len);
+                if (cmp < 0) {
+                        if (cur == lower)
+                                break;
+                        lower = cur;
+                } else if (cmp > 0) {
+                        if (cur == upper)
+                                break;
+                        upper = cur;
+                } else {
+                        debug("Found %s in blacklist", dgst_hex);
+                        ret = 1;
+                        break;
+                }
+        }
+
+out:
+        if (dgst_packed)
+                xfree(dgst_packed);
+        if (dgst_hex)
+                xfree(dgst_hex);
+        if (fd >= 0)
+                close(fd);
+        xfree(blacklist_file);
+        return ret;
+}