Bug#614897: openssh-client: ssh-add fails to read from FIFOs

[Daniel Kahn Gillmor <dkg@fifthhorseman.net>]

Package: openssh-client
Version: 1:5.8p1-2
Severity: normal
Tags: upstream patch

Sometimes, it's nice to have ssh-add read a key from a FIFO instead of
writing the key to a file.

older versions of ssh (before 5.7p1, i think) would let you do that.
5.8p1-2 doesn't.

here's an example (i know, the key is already in the filesystem; this
is just an example):

 ssh-keygen -t rsa -b 1024 -N '' -f test-key
 umask 077
 mfifo test-fifo
 ssh-add test-fifo &
 cat test-key > test-fifo

This no longer works :( It also means that "monkeysphere
subkey-to-ssh-agent" fails for users with openssh-client 5.8p1
installed.

I've reported the bug upstream at:

 https://bugzilla.mindrot.org/show_bug.cgi?id=1869

And i'm attaching a patch that fixes the problem right now by
attempting reads of up to 8KiB if ssh-add detects that the file it is
reading from is a FIFO.

It would be great if debian could adopt this patch so that
monkeysphere would work again until upstream adopts it.

Thanks for your work on OpenSSH for debian,

             --dkg

-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (500, 'testing'), (200, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 2.6.37-1-686 (SMP w/1 CPU core)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages openssh-client depends on:
ii  adduser              3.112+nmu2          add and remove users and groups
ii  debconf [debconf-2.0 1.5.38              Debian configuration management sy
ii  dpkg                 1.15.8.10           Debian package management system
ii  libc6                2.11.2-11           Embedded GNU C Library: Shared lib
ii  libedit2             2.11-20080614-2     BSD editline and history libraries
ii  libgssapi-krb5-2     1.8.3+dfsg-4        MIT Kerberos runtime libraries - k
ii  libselinux1          2.0.96-1            SELinux runtime shared libraries
ii  libssl0.9.8          0.9.8o-5            SSL shared libraries
ii  passwd               1:4.1.4.2+svn3283-3 change and administer password and
ii  zlib1g               1:1.2.3.4.dfsg-3    compression library - runtime

Versions of packages openssh-client recommends:
ii  openssh-blacklist             0.4.1      list of default blacklisted OpenSS
ii  openssh-blacklist-extra       0.4.1      list of non-default blacklisted Op
ii  xauth                         1:1.0.5-1  X authentication utility

Versions of packages openssh-client suggests:
pn  keychain                     <none>      (no description available)
pn  libpam-ssh                   <none>      (no description available)
ii  ssh-askpass                  1:1.2.4.1-9 under X, asks user for a passphras

-- no debconf information

=== modified file 'authfile.c'
--- authfile.c	2011-01-24 12:43:25 +0000
+++ authfile.c	2011-02-24 03:23:59 +0000
@@ -317,7 +317,7 @@
 static int
 key_load_file(int fd, const char *filename, Buffer *blob)
 {
-	size_t len;
+	size_t len,readcount;
 	u_char *cp;
 	struct stat st;
 
@@ -337,11 +337,14 @@
 		return 0;
 	}
 	len = (size_t)st.st_size;		/* truncated */
+	if (0 == len && S_ISFIFO(st.st_mode))
+		len = 8192; /* we will try reading up to 8KiB from a FIFO */
 
 	buffer_init(blob);
 	cp = buffer_append_space(blob, len);
 
-	if (atomicio(read, fd, cp, len) != len) {
+	readcount = atomicio(read, fd, cp, len);
+	if (readcount != len && !(readcount > 0 && S_ISFIFO(st.st_mode))) {
 		debug("%s: read from key file %.200s%sfailed: %.100s", __func__,
 		    filename == NULL ? "" : filename,
 		    filename == NULL ? "" : " ",