shadow: Fix CVE-2023-4641

shadow-utils: possible password leak during passwd(1) change

(From OE-Core rev: 3623f48ff73ad97f583172b7dbfcb56affc9353b)

Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 148 insertions, 0 deletions

diff --git a/meta/recipes-extended/shadow/files/CVE-2023-4641.patch b/meta/recipes-extended/shadow/files/CVE-2023-4641.patch
new file mode 100644
index 0000000000..1fabfe928e
--- /dev/null
+++ b/meta/recipes-extended/shadow/files/CVE-2023-4641.patch
@@ -0,0 +1,147 @@
+From 25dbe2ce166a13322b7536ff2f738786ea2e61e7 Mon Sep 17 00:00:00 2001
+From: Alejandro Colomar <alx@kernel.org>
+Date: Sat, 10 Jun 2023 16:20:05 +0200
+Subject: [PATCH] gpasswd(1): Fix password leak
+
+How to trigger this password leak?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When gpasswd(1) asks for the new password, it asks twice (as is usual
+for confirming the new password).  Each of those 2 password prompts
+uses agetpass() to get the password.  If the second agetpass() fails,
+the first password, which has been copied into the 'static' buffer
+'pass' via STRFCPY(), wasn't being zeroed.
+
+agetpass() is defined in <./libmisc/agetpass.c> (around line 91), and
+can fail for any of the following reasons:
+
+-  malloc(3) or readpassphrase(3) failure.
+
+   These are going to be difficult to trigger.  Maybe getting the system
+   to the limits of memory utilization at that exact point, so that the
+   next malloc(3) gets ENOMEM, and possibly even the OOM is triggered.
+   About readpassphrase(3), ENFILE and EINTR seem the only plausible
+   ones, and EINTR probably requires privilege or being the same user;
+   but I wouldn't discard ENFILE so easily, if a process starts opening
+   files.
+
+-  The password is longer than PASS_MAX.
+
+   The is plausible with physical access.  However, at that point, a
+   keylogger will be a much simpler attack.
+
+And, the attacker must be able to know when the second password is being
+introduced, which is not going to be easy.
+
+How to read the password after the leak?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Provoking the leak yourself at the right point by entering a very long
+password is easy, and inspecting the process stack at that point should
+be doable.  Try to find some consistent patterns.
+
+Then, search for those patterns in free memory, right after the victim
+leaks their password.
+
+Once you get the leak, a program should read all the free memory
+searching for patterns that gpasswd(1) leaves nearby the leaked
+password.
+
+On 6/10/23 03:14, Seth Arnold wrote:
+> An attacker process wouldn't be able to use malloc(3) for this task.
+> There's a handful of tools available for userspace to allocate memory:
+>
+> -  brk / sbrk
+> -  mmap MAP_ANONYMOUS
+> -  mmap /dev/zero
+> -  mmap some other file
+> -  shm_open
+> -  shmget
+>
+> Most of these return only pages of zeros to a process.  Using mmap of an
+> existing file, you can get some of the contents of the file demand-loaded
+> into the memory space on the first use.
+>
+> The MAP_UNINITIALIZED flag only works if the kernel was compiled with
+> CONFIG_MMAP_ALLOW_UNINITIALIZED.  This is rare.
+>
+> malloc(3) doesn't zero memory, to our collective frustration, but all the
+> garbage in the allocations is from previous allocations in the current
+> process.  It isn't leftover from other processes.
+>
+> The avenues available for reading the memory:
+> -  /dev/mem and /dev/kmem (requires root, not available with Secure Boot)
+> -  /proc/pid/mem (requires ptrace privileges, mediated by YAMA)
+> -  ptrace (requires ptrace privileges, mediated by YAMA)
+> -  causing memory to be swapped to disk, and then inspecting the swap
+>
+> These all require a certain amount of privileges.
+
+How to fix it?
+~~~~~~~~~~~~~~
+
+memzero(), which internally calls explicit_bzero(3), or whatever
+alternative the system provides with a slightly different name, will
+make sure that the buffer is zeroed in memory, and optimizations are not
+allowed to impede this zeroing.
+
+This is not really 100% effective, since compilers may place copies of
+the string somewhere hidden in the stack.  Those copies won't get zeroed
+by explicit_bzero(3).  However, that's arguably a compiler bug, since
+compilers should make everything possible to avoid optimizing strings
+that are later passed to explicit_bzero(3).  But we all know that
+sometimes it's impossible to have perfect knowledge in the compiler, so
+this is plausible.  Nevertheless, there's nothing we can do against such
+issues, except minimizing the time such passwords are stored in plain
+text.
+
+Security concerns
+~~~~~~~~~~~~~~~~~
+
+We believe this isn't easy to exploit.  Nevertheless, and since the fix
+is trivial, this fix should probably be applied soon, and backported to
+all supported distributions, to prevent someone else having more
+imagination than us to find a way.
+
+Affected versions
+~~~~~~~~~~~~~~~~~
+
+All.  Bug introduced in shadow 19990709.  That's the second commit in
+the git history.
+
+Fixes: 45c6603cc86c ("[svn-upgrade] Integrating new upstream version, shadow (19990709)")
+
+CVE: CVE-2023-4641
+Upstream-Status: Backport [https://github.com/shadow-maint/shadow/commit/65c88a43a23c2391dcc90c0abda3e839e9c57904]
+
+Reported-by: Alejandro Colomar <alx@kernel.org>
+Cc: Serge Hallyn <serge@hallyn.com>
+Cc: Iker Pedrosa <ipedrosa@redhat.com>
+Cc: Seth Arnold <seth.arnold@canonical.com>
+Cc: Christian Brauner <christian@brauner.io>
+Cc: Balint Reczey <rbalint@debian.org>
+Cc: Sam James <sam@gentoo.org>
+Cc: David Runge <dvzrv@archlinux.org>
+Cc: Andreas Jaeger <aj@suse.de>
+Cc: <~hallyn/shadow@lists.sr.ht>
+Signed-off-by: Alejandro Colomar <alx@kernel.org>
+Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
+---
+ src/gpasswd.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/src/gpasswd.c b/src/gpasswd.c
+index 5983f787..2d8869ef 100644
+--- a/src/gpasswd.c
++++ b/src/gpasswd.c
+@@ -896,6 +896,7 @@ static void change_passwd (struct group *gr)
+                strzero (cp);
+                cp = getpass (_("Re-enter new password: "));
+                if (NULL == cp) {
++                       memzero (pass, sizeof pass);
+                        exit (1);
+                }
+ 
+-- 
+2.34.1
+
diff --git a/meta/recipes-extended/shadow/shadow.inc b/meta/recipes-extended/shadow/shadow.inc
index cf05a3af93..4014baddc1 100644
--- a/meta/recipes-extended/shadow/shadow.inc
+++ b/meta/recipes-extended/shadow/shadow.inc
@@ -17,6 +17,7 @@ SRC_URI = "${GITHUB_BASE_URI}/download/${PV}/${BP}.tar.gz \
            file://0001-Fix-can-not-print-full-login.patch \
            file://CVE-2023-29383.patch \
            file://0001-Overhaul-valid_field.patch \
+           file://CVE-2023-4641.patch \
            "
 
 SRC_URI:append:class-target = " \