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-rw-r--r--debian/patches-rt/0284-signal-Prevent-double-free-of-user-struct.patch52
1 files changed, 52 insertions, 0 deletions
diff --git a/debian/patches-rt/0284-signal-Prevent-double-free-of-user-struct.patch b/debian/patches-rt/0284-signal-Prevent-double-free-of-user-struct.patch
new file mode 100644
index 000000000..8a50b4089
--- /dev/null
+++ b/debian/patches-rt/0284-signal-Prevent-double-free-of-user-struct.patch
@@ -0,0 +1,52 @@
+From 9a8853e64ab5f1c44db176464996da3ba86d2a8e Mon Sep 17 00:00:00 2001
+From: Matt Fleming <matt@codeblueprint.co.uk>
+Date: Tue, 7 Apr 2020 10:54:13 +0100
+Subject: [PATCH 284/323] signal: Prevent double-free of user struct
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
+
+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>
+---
+ kernel/signal.c | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/kernel/signal.c b/kernel/signal.c
+index e1f263cbcf09..a1eeecb4922d 100644
+--- a/kernel/signal.c
++++ b/kernel/signal.c
+@@ -495,8 +495,8 @@ 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);
+ }
+--
+2.43.0
+