4.4-stable patches

added patches:
	don-t-dump-the-threads-that-had-been-already-exiting-when-zapped.patch

diff --git a/queue-4.4/don-t-dump-the-threads-that-had-been-already-exiting-when-zapped.patch b/queue-4.4/don-t-dump-the-threads-that-had-been-already-exiting-when-zapped.patch
new file mode 100644 (file)
index 0000000..2678417
--- /dev/null
+++ b/queue-4.4/don-t-dump-the-threads-that-had-been-already-exiting-when-zapped.patch
@@ -0,0 +1,72 @@
+From 77f6ab8b7768cf5e6bdd0e72499270a0671506ee Mon Sep 17 00:00:00 2001
+From: Al Viro <viro@zeniv.linux.org.uk>
+Date: Wed, 28 Oct 2020 16:39:49 -0400
+Subject: don't dump the threads that had been already exiting when zapped.
+
+From: Al Viro <viro@zeniv.linux.org.uk>
+
+commit 77f6ab8b7768cf5e6bdd0e72499270a0671506ee upstream.
+
+Coredump logics needs to report not only the registers of the dumping
+thread, but (since 2.5.43) those of other threads getting killed.
+
+Doing that might require extra state saved on the stack in asm glue at
+kernel entry; signal delivery logics does that (we need to be able to
+save sigcontext there, at the very least) and so does seccomp.
+
+That covers all callers of do_coredump().  Secondary threads get hit with
+SIGKILL and caught as soon as they reach exit_mm(), which normally happens
+in signal delivery, so those are also fine most of the time.  Unfortunately,
+it is possible to end up with secondary zapped when it has already entered
+exit(2) (or, worse yet, is oopsing).  In those cases we reach exit_mm()
+when mm->core_state is already set, but the stack contents is not what
+we would have in signal delivery.
+
+At least on two architectures (alpha and m68k) it leads to infoleaks - we
+end up with a chunk of kernel stack written into coredump, with the contents
+consisting of normal C stack frames of the call chain leading to exit_mm()
+instead of the expected copy of userland registers.  In case of alpha we
+leak 312 bytes of stack.  Other architectures (including the regset-using
+ones) might have similar problems - the normal user of regsets is ptrace
+and the state of tracee at the time of such calls is special in the same
+way signal delivery is.
+
+Note that had the zapper gotten to the exiting thread slightly later,
+it wouldn't have been included into coredump anyway - we skip the threads
+that have already cleared their ->mm.  So let's pretend that zapper always
+loses the race.  IOW, have exit_mm() only insert into the dumper list if
+we'd gotten there from handling a fatal signal[*]
+
+As the result, the callers of do_exit() that have *not* gone through get_signal()
+are not seen by coredump logics as secondary threads.  Which excludes voluntary
+exit()/oopsen/traps/etc.  The dumper thread itself is unaffected by that,
+so seccomp is fine.
+
+[*] originally I intended to add a new flag in tsk->flags, but ebiederman pointed
+out that PF_SIGNALED is already doing just what we need.
+
+Cc: stable@vger.kernel.org
+Fixes: d89f3847def4 ("[PATCH] thread-aware coredumps, 2.5.43-C3")
+History-tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
+Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ kernel/exit.c |    5 ++++-
+ 1 file changed, 4 insertions(+), 1 deletion(-)
+
+--- a/kernel/exit.c
++++ b/kernel/exit.c
+@@ -408,7 +408,10 @@ static void exit_mm(struct task_struct *
+               up_read(&mm->mmap_sem);
+ 
+               self.task = tsk;
+-              self.next = xchg(&core_state->dumper.next, &self);
++              if (self.task->flags & PF_SIGNALED)
++                      self.next = xchg(&core_state->dumper.next, &self);
++              else
++                      self.task = NULL;
+               /*
+                * Implies mb(), the result of xchg() must be visible
+                * to core_state->dumper.

diff --git a/queue-4.4/series b/queue-4.4/series
index 0fa85ef9ff3efb9748445e8eb1396773e2b8e974..8dd61e3a57e7d768beb8f3b2a6d5e031484a0e4a 100644 (file)
--- a/queue-4.4/series
+++ b/queue-4.4/series
@@ -34,3 +34,4 @@ ext4-unlock-xattr_sem-properly-in-ext4_inline_data_truncate.patch
 usb-cdc-acm-add-disable_echo-for-renesas-usb-download-mode.patch
 mei-protect-mei_cl_mtu-from-null-dereference.patch
 ocfs2-initialize-ip_next_orphan.patch
+don-t-dump-the-threads-that-had-been-already-exiting-when-zapped.patch