59 lines
2.1 KiB
Diff
59 lines
2.1 KiB
Diff
From 739f241c793a4258729c6ededd6ec4c02093ac7d Mon Sep 17 00:00:00 2001
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Message-Id: <739f241c793a4258729c6ededd6ec4c02093ac7d.1601675153.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Matt Fleming <matt@codeblueprint.co.uk>
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Date: Tue, 7 Apr 2020 10:54:13 +0100
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Subject: [PATCH 329/333] signal: Prevent double-free of user struct
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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[ Upsteam commit 9567db2ebe566a93485e1a27d8759969d0002d7a ]
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The way user struct reference counting works changed significantly with,
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fda31c50292a ("signal: avoid double atomic counter increments for user accounting")
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Now user structs are only freed once the last pending signal is
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dequeued. Make sigqueue_free_current() follow this new convention to
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avoid freeing the user struct multiple times and triggering this
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warning:
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refcount_t: underflow; use-after-free.
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WARNING: CPU: 0 PID: 6794 at lib/refcount.c:288 refcount_dec_not_one+0x45/0x50
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Call Trace:
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refcount_dec_and_lock_irqsave+0x16/0x60
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free_uid+0x31/0xa0
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__dequeue_signal+0x17c/0x190
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dequeue_signal+0x5a/0x1b0
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do_sigtimedwait+0x208/0x250
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__x64_sys_rt_sigtimedwait+0x6f/0xd0
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do_syscall_64+0x72/0x200
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entry_SYSCALL_64_after_hwframe+0x49/0xbe
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Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
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Reported-by: Daniel Wagner <wagi@monom.org>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Tom Zanussi <zanussi@kernel.org>
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---
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kernel/signal.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/kernel/signal.c b/kernel/signal.c
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index 45748993f777..05c9b5a6b3ae 100644
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--- a/kernel/signal.c
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+++ b/kernel/signal.c
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@@ -488,8 +488,8 @@ static void sigqueue_free_current(struct sigqueue *q)
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up = q->user;
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if (rt_prio(current->normal_prio) && !put_task_cache(current, q)) {
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- atomic_dec(&up->sigpending);
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- free_uid(up);
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+ if (atomic_dec_and_test(&up->sigpending))
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+ free_uid(up);
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} else
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__sigqueue_free(q);
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}
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--
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2.17.1
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