gnu: guile-ssh: Fix potential double-free/use-after-free issue.

Fixes <http://bugs.gnu.org/26976>.
Reported by Mark H Weaver <mhw@netris.org>.

* gnu/packages/patches/guile-ssh-double-free.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/ssh.scm (guile-ssh)[source](patches): Add it.

gnu/local.mk

@@ -654,6 +654,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/guile-relocatable.patch			\
   %D%/packages/patches/guile-rsvg-pkgconfig.patch		\
   %D%/packages/patches/guile-ssh-rexec-bug.patch		\
+  %D%/packages/patches/guile-ssh-double-free.patch		\
   %D%/packages/patches/gtk2-respect-GUIX_GTK2_PATH.patch	\
   %D%/packages/patches/gtk2-respect-GUIX_GTK2_IM_MODULE_FILE.patch \
   %D%/packages/patches/gtk2-theme-paths.patch			\

gnu/packages/patches/guile-ssh-double-free.patch

@@ -0,0 +1,37 @@
+Fix a double-free or use-after-free issue with Guile-SSH used
+with Guile 2.2.  See <https://bugs.gnu.org/26976>.
+
+diff --git a/libguile-ssh/channel-type.c b/libguile-ssh/channel-type.c
+index 3dd641f..0839854 100644
+--- a/libguile-ssh/channel-type.c
++++ b/libguile-ssh/channel-type.c
+@@ -229,10 +229,11 @@ ptob_close (SCM channel)
+       ssh_channel_free (ch->ssh_channel);
+     }
+ 
++  SCM_SETSTREAM (channel, NULL);
++
+ #if USING_GUILE_BEFORE_2_2
+   scm_gc_free (pt->write_buf, pt->write_buf_size, "port write buffer");
+   scm_gc_free (pt->read_buf,  pt->read_buf_size, "port read buffer");
+-  SCM_SETSTREAM (channel, NULL);
+ 
+   return 0;
+ #endif
+diff --git a/libguile-ssh/sftp-file-type.c b/libguile-ssh/sftp-file-type.c
+index 8879924..f87cf03 100644
+--- a/libguile-ssh/sftp-file-type.c
++++ b/libguile-ssh/sftp-file-type.c
+@@ -224,10 +224,11 @@ ptob_close (SCM sftp_file)
+       sftp_close (fd->file);
+     }
+ 
++  SCM_SETSTREAM (sftp_file, NULL);
++
+ #if USING_GUILE_BEFORE_2_2
+   scm_gc_free (pt->write_buf, pt->write_buf_size, "port write buffer");
+   scm_gc_free (pt->read_buf,  pt->read_buf_size, "port read buffer");
+-  SCM_SETSTREAM (sftp_file, NULL);
+ 
+   return 1;
+ #endif

gnu/packages/ssh.scm

@@ -226,7 +226,8 @@ Additionally, various channel-specific options can be negotiated.")
               (sha256
                (base32
                 "0r261i8kc3avbmbwgyzak2vnqwssjlgz37g2y2fwm80w9bmn2m7j"))
-              (patches (search-patches "guile-ssh-rexec-bug.patch"))
+              (patches (search-patches "guile-ssh-rexec-bug.patch"
+                                       "guile-ssh-double-free.patch"))
               (modules '((guix build utils)))
               (snippet
                ;; 'configure.ac' mistakenly tries to link files from examples/