screen: Fix CVE-2025-46805

Upstream-Status: Backport from https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=161f85b98b7e1d5e4893aeed20f4cdb5e3dfaaa4

(From OE-Core rev: b25b0f785e0b7650e31a45a92be196be6b76ea78)

Signed-off-by: Hitendra Prajapati <hprajapati@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 122 insertions, 0 deletions

diff --git a/meta/recipes-extended/screen/screen/CVE-2025-46805.patch b/meta/recipes-extended/screen/screen/CVE-2025-46805.patch
new file mode 100644
index 0000000000..9d9d3e2827
--- /dev/null
+++ b/meta/recipes-extended/screen/screen/CVE-2025-46805.patch
@@ -0,0 +1,121 @@
+From 161f85b98b7e1d5e4893aeed20f4cdb5e3dfaaa4 Mon Sep 17 00:00:00 2001
+From: Matthias Gerstner <matthias.gerstner@suse.de>
+Date: Mon, 12 May 2025 15:38:19 +0200
+Subject: fix CVE-2025-46805: socket.c - don't send signals with root
+ privileges
+
+The CheckPid() function was introduced to address CVE-2023-24626, to
+prevent sending SIGCONT and SIGHUP to arbitrary PIDs in the system. This
+fix still suffers from a TOCTOU race condition. The client can replace
+itself by a privileged process, or try to cycle PIDs until a privileged
+process receives the original PID.
+
+To prevent this, always send signals using the real privileges. Keep
+CheckPid() for error diagnostics. If sending the actual signal fails
+later on then there will be no more error reporting.
+
+It seems the original bugfix already introduced a regression when
+attaching to another's user session that is not owned by root. In this
+case the target sessions runs with real uid X, while for sending a
+signal to the `pid` provided by the client real uid Y (or root
+privileges) are required.
+
+This is hard to properly fix without this regression. On Linux pidfds
+could be used to allow safely sending signals to other PIDs as root
+without involving race conditions. In this case the client PID should
+also be obtained via the UNIX domain socket's SO_PEERCRED option,
+though.
+
+Upstream-Status: Backport [https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=161f85b98b7e1d5e4893aeed20f4cdb5e3dfaaa4]
+CVE: CVE-2025-46805
+Signed-off-by: Hitendra Prajapati <hprajapati@mvista.com>
+---
+ socket.c | 21 +++++++++++++--------
+ 1 file changed, 13 insertions(+), 8 deletions(-)
+
+diff --git a/socket.c b/socket.c
+index 9d87445..3bbd64e 100644
+--- a/socket.c
++++ b/socket.c
+@@ -826,6 +826,11 @@ int pid;
+   return UserStatus();
+ }
+ 
++static void KillUnpriv(pid_t pid, int sig) {
++    UserContext();
++    UserReturn(kill(pid, sig));
++}
++
+ #ifdef hpux
+ /*
+  * From: "F. K. Bruner" <napalm@ugcs.caltech.edu>
+@@ -911,14 +916,14 @@ struct win *wi;
+             {
+              Msg(errno, "Could not perform necessary sanity checks on pts device.");
+              close(i);
+-             Kill(pid, SIG_BYE);
++             KillUnpriv(pid, SIG_BYE);
+              return -1;
+             }
+           if (strcmp(ttyname_in_ns, m->m_tty))
+             {
+              Msg(errno, "Attach: passed fd does not match tty: %s - %s!", ttyname_in_ns, m->m_tty[0] != '\0' ? m->m_tty : "(null)");
+              close(i);
+-             Kill(pid, SIG_BYE);
++             KillUnpriv(pid, SIG_BYE);
+              return -1;
+            }
+          /* m->m_tty so far contains the actual name of the pts device in the
+@@ -935,19 +940,19 @@ struct win *wi;
+        {
+          Msg(errno, "Attach: passed fd does not match tty: %s - %s!", m->m_tty, myttyname ? myttyname : "NULL");
+          close(i);
+-         Kill(pid, SIG_BYE);
++         KillUnpriv(pid, SIG_BYE);
+          return -1;
+        }
+     }
+   else if ((i = secopen(m->m_tty, O_RDWR | O_NONBLOCK, 0)) < 0)
+     {
+       Msg(errno, "Attach: Could not open %s!", m->m_tty);
+-      Kill(pid, SIG_BYE);
++      KillUnpriv(pid, SIG_BYE);
+       return -1;
+     }
+ #ifdef MULTIUSER
+   if (attach)
+-    Kill(pid, SIGCONT);
++    KillUnpriv(pid, SIGCONT);
+ #endif
+ 
+ #if defined(ultrix) || defined(pyr) || defined(NeXT)
+@@ -960,7 +965,7 @@ struct win *wi;
+        {
+          write(i, "Attaching from inside of screen?\n", 33);
+          close(i);
+-         Kill(pid, SIG_BYE);
++         KillUnpriv(pid, SIG_BYE);
+          Msg(0, "Attach msg ignored: coming from inside.");
+          return -1;
+        }
+@@ -971,7 +976,7 @@ struct win *wi;
+          {
+              write(i, "Access to session denied.\n", 26);
+              close(i);
+-             Kill(pid, SIG_BYE);
++             KillUnpriv(pid, SIG_BYE);
+              Msg(0, "Attach: access denied for user %s.", user);
+              return -1;
+          }
+@@ -1289,7 +1294,7 @@ ReceiveMsg()
+             Msg(0, "Query attempt with bad pid(%d)!", m.m.command.apid);
+           }
+           else {
+-            Kill(m.m.command.apid,
++            KillUnpriv(m.m.command.apid,
+                (queryflag >= 0)
+                    ? SIGCONT
+                    : SIG_BYE); /* Send SIG_BYE if an error happened */
+-- 
+2.49.0
+
diff --git a/meta/recipes-extended/screen/screen_4.9.0.bb b/meta/recipes-extended/screen/screen_4.9.0.bb
index 19070d87d8..d137c85600 100644
--- a/meta/recipes-extended/screen/screen_4.9.0.bb
+++ b/meta/recipes-extended/screen/screen_4.9.0.bb
@@ -22,6 +22,7 @@ SRC_URI = "${GNU_MIRROR}/screen/screen-${PV}.tar.gz \
            file://0001-fix-for-multijob-build.patch \
            file://0001-Remove-more-compatibility-stuff.patch \
            file://CVE-2023-24626.patch \
+           file://CVE-2025-46805.patch \
           "
 
 SRC_URI[sha256sum] = "f9335281bb4d1538ed078df78a20c2f39d3af9a4e91c57d084271e0289c730f4"