screen: fix CVE-2025-46802

For a short time they PTY is set to mode 666, allowing any user on the
system to connect to the screen session.

Reference:
https://security-tracker.debian.org/tracker/CVE-2025-46802

Upstream-patch:
https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=049b26b22e197ba3be9c46e5c193032e01a4724a

(From OE-Core rev: b17e091eb4681b69c5a050d3fa0f9289f524e205)

Signed-off-by: Divya Chellam <divya.chellam@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 147 insertions, 0 deletions

diff --git a/meta/recipes-extended/screen/screen/CVE-2025-46802.patch b/meta/recipes-extended/screen/screen/CVE-2025-46802.patch
new file mode 100644
index 0000000000..e46affc480
--- /dev/null
+++ b/meta/recipes-extended/screen/screen/CVE-2025-46802.patch
@@ -0,0 +1,146 @@
+From 049b26b22e197ba3be9c46e5c193032e01a4724a Mon Sep 17 00:00:00 2001
+From: Matthias Gerstner <matthias.gerstner@suse.de>
+Date: Mon, 12 May 2025 15:15:38 +0200
+Subject: [PATCH] fix CVE-2025-46802: attacher.c - prevent temporary 0666 mode
+ on PTYs
+
+This temporary chmod of the PTY to mode 0666 is most likely a remnant of
+past times, before the PTY file descriptor was passed to the target
+session via the UNIX domain socket.
+
+This chmod() causes a race condition during which any other user in the
+system can open the PTY for reading and writing, and thus allows PTY
+hijacking.
+
+Simply remove this logic completely.
+
+CVE: CVE-2025-46802
+
+Upstream-Status: Backport [https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=049b26b22e197ba3be9c46e5c193032e01a4724a]
+
+Signed-off-by: Divya Chellam <divya.chellam@windriver.com>
+---
+ attacher.c | 27 ---------------------------
+ screen.c   | 19 -------------------
+ 2 files changed, 46 deletions(-)
+
+diff --git a/attacher.c b/attacher.c
+index c35ae7a..16b151e 100644
+--- a/attacher.c
++++ b/attacher.c
+@@ -73,7 +73,6 @@ extern int MasterPid, attach_fd;
+ #ifdef MULTIUSER
+ extern char *multi;
+ extern int multiattach, multi_uid, own_uid;
+-extern int tty_mode, tty_oldmode;
+ # ifndef USE_SETEUID
+ static int multipipe[2];
+ # endif
+@@ -160,9 +159,6 @@ int how;
+ 
+       if (pipe(multipipe))
+        Panic(errno, "pipe");
+-      if (chmod(attach_tty, 0666))
+-       Panic(errno, "chmod %s", attach_tty);
+-      tty_oldmode = tty_mode;
+       eff_uid = -1;    /* make UserContext fork */
+       real_uid = multi_uid;
+       if ((ret = UserContext()) <= 0)
+@@ -174,11 +170,6 @@ int how;
+            Panic(errno, "UserContext");
+          close(multipipe[1]);
+          read(multipipe[0], &dummy, 1);
+-         if (tty_oldmode >= 0)
+-           {
+-             chmod(attach_tty, tty_oldmode);
+-             tty_oldmode = -1;
+-           }
+          ret = UserStatus();
+ #ifdef LOCK
+          if (ret == SIG_LOCK)
+@@ -224,9 +215,6 @@ int how;
+       xseteuid(multi_uid);
+       xseteuid(own_uid);
+ #endif
+-      if (chmod(attach_tty, 0666))
+-       Panic(errno, "chmod %s", attach_tty);
+-      tty_oldmode = tty_mode;
+     }
+ # endif /* USE_SETEUID */
+ #endif /* MULTIUSER */
+@@ -423,13 +411,6 @@ int how;
+       ContinuePlease = 0;
+ # ifndef USE_SETEUID
+       close(multipipe[1]);
+-# else
+-      xseteuid(own_uid);
+-      if (tty_oldmode >= 0)
+-        if (chmod(attach_tty, tty_oldmode))
+-          Panic(errno, "chmod %s", attach_tty);
+-      tty_oldmode = -1;
+-      xseteuid(real_uid);
+ # endif
+     }
+ #endif
+@@ -505,14 +486,6 @@ AttacherFinit SIGDEFARG
+          close(s);
+        }
+     }
+-#ifdef MULTIUSER
+-  if (tty_oldmode >= 0)
+-    {
+-      if (setuid(own_uid))
+-        Panic(errno, "setuid");
+-      chmod(attach_tty, tty_oldmode);
+-    }
+-#endif
+   exit(0);
+   SIGRETURN;
+ }
+diff --git a/screen.c b/screen.c
+index 7653cd1..1a23e1a 100644
+--- a/screen.c
++++ b/screen.c
+@@ -230,8 +230,6 @@ char *multi_home;
+ int multi_uid;
+ int own_uid;
+ int multiattach;
+-int tty_mode;
+-int tty_oldmode = -1;
+ #endif
+ 
+ char HostName[MAXSTR];
+@@ -1009,9 +1007,6 @@ int main(int ac, char** av)
+ 
+     /* ttyname implies isatty */
+     SetTtyname(true, &st);
+-#ifdef MULTIUSER
+-    tty_mode = (int)st.st_mode & 0777;
+-#endif
+ 
+     fl = fcntl(0, F_GETFL, 0);
+     if (fl != -1 && (fl & (O_RDWR|O_RDONLY|O_WRONLY)) == O_RDWR)
+@@ -2170,20 +2165,6 @@ DEFINE_VARARGS_FN(Panic)
+       if (D_userpid)
+         Kill(D_userpid, SIG_BYE);
+     }
+-#ifdef MULTIUSER
+-  if (tty_oldmode >= 0) {
+-
+-# ifdef USE_SETEUID
+-    if (setuid(own_uid))
+-      xseteuid(own_uid);       /* may be a loop. sigh. */
+-# else
+-      setuid(own_uid);
+-# endif
+-
+-    debug1("Panic: changing back modes from %s\n", attach_tty);
+-    chmod(attach_tty, tty_oldmode);
+-  }
+-#endif
+   eexit(1);
+ }
+ 
+-- 
+2.40.0
+
diff --git a/meta/recipes-extended/screen/screen_4.9.1.bb b/meta/recipes-extended/screen/screen_4.9.1.bb
index 96f8021255..bc4928ff77 100644
--- a/meta/recipes-extended/screen/screen_4.9.1.bb
+++ b/meta/recipes-extended/screen/screen_4.9.1.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-2025-46805.patch \
+           file://CVE-2025-46802.patch \
            "
 
 SRC_URI[sha256sum] = "26cef3e3c42571c0d484ad6faf110c5c15091fbf872b06fa7aa4766c7405ac69"