From 8e2028c4cbc41caae5551c2cd8cd0d7533bf1749 Mon Sep 17 00:00:00 2001 Message-Id: <8e2028c4cbc41caae5551c2cd8cd0d7533bf1749.1599166691.git.zanussi@kernel.org> In-Reply-To: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org> References: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org> From: Matt Fleming Date: Tue, 7 Apr 2020 10:54:13 +0100 Subject: [PATCH 329/333] signal: Prevent double-free of user struct Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.142-rt63.tar.xz [ 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 Reported-by: Daniel Wagner Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Tom Zanussi --- kernel/signal.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 45748993f777..05c9b5a6b3ae 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -488,8 +488,8 @@ 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); } -- 2.17.1