linux-kernel - [PATCH 3.16 128/148] ACPI: OSL: only free map once in osl.c

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Message-ID: <lsq.1581185941.37930925@decadent.org.uk>
Date:   Sat, 08 Feb 2020 18:21:07 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Dmitry Safonov" <0x7f454c46@...il.com>,
        "Francesco Ruggeri" <fruggeri@...sta.com>
Subject: [PATCH 3.16 128/148] ACPI: OSL: only free map once in osl.c

3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Francesco Ruggeri <fruggeri@...sta.com>

commit 833a426cc471b6088011b3d67f1dc4e147614647 upstream.

acpi_os_map_cleanup checks map->refcount outside of acpi_ioremap_lock
before freeing the map. This creates a race condition the can result
in the map being freed more than once.
A panic can be caused by running

for ((i=0; i<10; i++))
do
        for ((j=0; j<100000; j++))
        do
                cat /sys/firmware/acpi/tables/data/BERT >/dev/null
        done &
done

This patch makes sure that only the process that drops the reference
to 0 does the freeing.

Fixes: b7c1fadd6c2e ("ACPI: Do not use krefs under a mutex in osl.c")
Signed-off-by: Francesco Ruggeri <fruggeri@...sta.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@...il.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/acpi/osl.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -416,24 +416,27 @@ acpi_os_map_memory(acpi_physical_address
 }
 EXPORT_SYMBOL_GPL(acpi_os_map_memory);
 
-static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
+/* Must be called with mutex_lock(&acpi_ioremap_lock) */
+static unsigned long acpi_os_drop_map_ref(struct acpi_ioremap *map)
 {
-	if (!--map->refcount)
+	unsigned long refcount = --map->refcount;
+
+	if (!refcount)
 		list_del_rcu(&map->list);
+	return refcount;
 }
 
 static void acpi_os_map_cleanup(struct acpi_ioremap *map)
 {
-	if (!map->refcount) {
-		synchronize_rcu_expedited();
-		acpi_unmap(map->phys, map->virt);
-		kfree(map);
-	}
+	synchronize_rcu_expedited();
+	acpi_unmap(map->phys, map->virt);
+	kfree(map);
 }
 
 void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
 {
 	struct acpi_ioremap *map;
+	unsigned long refcount;
 
 	if (!acpi_gbl_permanent_mmap) {
 		__acpi_unmap_table(virt, size);
@@ -447,10 +450,11 @@ void __ref acpi_os_unmap_iomem(void __io
 		WARN(true, PREFIX "%s: bad address %p\n", __func__, virt);
 		return;
 	}
-	acpi_os_drop_map_ref(map);
+	refcount = acpi_os_drop_map_ref(map);
 	mutex_unlock(&acpi_ioremap_lock);
 
-	acpi_os_map_cleanup(map);
+	if (!refcount)
+		acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL_GPL(acpi_os_unmap_iomem);
 
@@ -491,6 +495,7 @@ void acpi_os_unmap_generic_address(struc
 {
 	u64 addr;
 	struct acpi_ioremap *map;
+	unsigned long refcount;
 
 	if (gas->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY)
 		return;
@@ -506,10 +511,11 @@ void acpi_os_unmap_generic_address(struc
 		mutex_unlock(&acpi_ioremap_lock);
 		return;
 	}
-	acpi_os_drop_map_ref(map);
+	refcount = acpi_os_drop_map_ref(map);
 	mutex_unlock(&acpi_ioremap_lock);
 
-	acpi_os_map_cleanup(map);
+	if (!refcount)
+		acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL(acpi_os_unmap_generic_address);