1 files changed, 51 insertions, 0 deletions
diff --git a/debian/patches-rt/0328-signal-Prevent-double-free-of-user-struct.patch b/debian/patches-rt/0328-signal-Prevent-double-free-of-user-struct.patch
new file mode 100644
index 000000000..728a5ce48
--- /dev/null
+++ b/debian/patches-rt/0328-signal-Prevent-double-free-of-user-struct.patch
@@ -0,0 +1,51 @@
+From: Matt Fleming <matt@codeblueprint.co.uk>
+Date: Tue, 7 Apr 2020 10:54:13 +0100
+Subject: [PATCH 328/342] signal: Prevent double-free of user struct
+Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=c247eea7618fab8dc4ca5b123a7708de3550a64b
+
+[ Upsteam commit 9567db2ebe566a93485e1a27d8759969d0002d7a ]
+
+The way user struct reference counting works changed significantly with,
+
+  fda31c50292a ("signal: avoid double atomic counter increments for user accounting")
+
+Now user structs are only freed once the last pending signal is
+dequeued. Make sigqueue_free_current() follow this new convention to
+avoid freeing the user struct multiple times and triggering this
+warning:
+
+ refcount_t: underflow; use-after-free.
+ WARNING: CPU: 0 PID: 6794 at lib/refcount.c:288 refcount_dec_not_one+0x45/0x50
+ Call Trace:
+  refcount_dec_and_lock_irqsave+0x16/0x60
+  free_uid+0x31/0xa0
+  __dequeue_signal+0x17c/0x190
+  dequeue_signal+0x5a/0x1b0
+  do_sigtimedwait+0x208/0x250
+  __x64_sys_rt_sigtimedwait+0x6f/0xd0
+  do_syscall_64+0x72/0x200
+  entry_SYSCALL_64_after_hwframe+0x49/0xbe
+
+Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
+Reported-by: Daniel Wagner <wagi@monom.org>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Signed-off-by: Tom Zanussi <zanussi@kernel.org>
+---
+ kernel/signal.c | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/kernel/signal.c b/kernel/signal.c
+index 730ac7ff4637..0cabba4cfd7f 100644
+--- a/kernel/signal.c
++++ b/kernel/signal.c
+@@ -489,8 +489,8 @@ static void sigqueue_free_current(struct sigqueue *q)
+ 
+ 	up = q->user;
+ 	if (rt_prio(current->normal_prio) && !put_task_cache(current, q)) {
+-		atomic_dec(&up->sigpending);
+-		free_uid(up);
++		if (atomic_dec_and_test(&up->sigpending))
++			free_uid(up);
+ 	} else
+ 		  __sigqueue_free(q);
+ }