acpi/nfit: Fix race accessing memdev in nfit_get_smbios_id()

Commit Message

Tony Luck Jan. 11, 2019, 10:46 p.m. UTC

Possible race accessing memdev structures after dropping the
mutex. Dan Williams says this could race against another thread
that is doing:

 # echo "ACPI0012:00" > /sys/bus/acpi/drivers/nfit/unbind

Reported-by: Jane Chu <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>
---

This time with a commit message and credit to Jane for finding it.

 drivers/acpi/nfit/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Dan Williams Jan. 11, 2019, 11:06 p.m. UTC | #1

On Fri, Jan 11, 2019 at 2:46 PM Luck, Tony <[e-mail]> wrote:
>
>
> Possible race accessing memdev structures after dropping the
> mutex. Dan Williams says this could race against another thread
> that is doing:
>
>  # echo "ACPI0012:00" > /sys/bus/acpi/drivers/nfit/unbind
>
> Reported-by: Jane Chu <[e-mail]>
> Signed-off-by: Tony Luck <[e-mail]>
> ---
>
> This time with a commit message and credit to Jane for finding it.

Thanks, applied.

Patch

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 011d3db19c80..22945bf803c8 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -721,6 +721,7 @@  int nfit_get_smbios_id(u32 device_handle, u16 *flags)
 	struct acpi_nfit_memory_map *memdev;
 	struct acpi_nfit_desc *acpi_desc;
 	struct nfit_mem *nfit_mem;
+	u16 physical_id;
 
 	mutex_lock(&acpi_desc_lock);
 	list_for_each_entry(acpi_desc, &acpi_descs, list) {
@@ -728,10 +729,11 @@  int nfit_get_smbios_id(u32 device_handle, u16 *flags)
 		list_for_each_entry(nfit_mem, &acpi_desc->dimms, list) {
 			memdev = __to_nfit_memdev(nfit_mem);
 			if (memdev->device_handle == device_handle) {
+				*flags = memdev->flags;
+				physical_id = memdev->physical_id;
 				mutex_unlock(&acpi_desc->init_mutex);
 				mutex_unlock(&acpi_desc_lock);
-				*flags = memdev->flags;
-				return memdev->physical_id;
+				return physical_id;
 			}
 		}
 		mutex_unlock(&acpi_desc->init_mutex);