Copied from Debian.

From: Petr Stodulka <pstodulk@redhat.com>
Date: Mon, 14 Sep 2015 18:23:17 +0200
Subject: Upstream fix for heap overflow
Bug-Debian: https://bugs.debian.org/802162
Bug-RedHat: https://bugzilla.redhat.com/show_bug.cgi?id=1260944
Origin: https://bugzilla.redhat.com/attachment.cgi?id=1073002
Forwarded: yes

---
 crypt.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/crypt.c
+++ b/crypt.c
@@ -465,7 +465,17 @@
     GLOBAL(pInfo->encrypted) = FALSE;
     defer_leftover_input(__G);
     for (n = 0; n < RAND_HEAD_LEN; n++) {
-        b = NEXTBYTE;
+        /* 2012-11-23 SMS.  (OUSPG report.)
+         * Quit early if compressed size < HEAD_LEN.  The resulting
+         * error message ("unable to get password") could be improved,
+         * but it's better than trying to read nonexistent data, and
+         * then continuing with a negative G.csize.  (See
+         * fileio.c:readbyte()).
+         */
+        if ((b = NEXTBYTE) == (ush)EOF)
+        {
+            return PK_ERR;
+        }
         h[n] = (uch)b;
         Trace((stdout, " (%02x)", h[n]));
     }
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