2022-12-14 14:41:33

by Hector Martin

Subject: [PATCH] nvmem: core: Fix race in nvmem_register()

nvmem_register() currently registers the device before adding the nvmem
cells, which creates a race window where consumers may find the nvmem
device (and not get PROBE_DEFERred), but then fail to find the cells and
error out.

Move device registration to the end of nvmem_register(), to close the
race.

Observed when the stars line up on Apple Silicon machines with the (not
yet upstream, but trivial) spmi nvmem driver and the macsmc-rtc client:

[ 0.487375] macsmc-rtc macsmc-rtc: error -ENOENT: Failed to get rtc_offset NVMEM cell

Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
Signed-off-by: Hector Martin <[email protected]>
---
drivers/nvmem/core.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 321d7d63e068..d255feca5e17 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -837,20 +837,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)

dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);

- rval = device_register(&nvmem->dev);
- if (rval)
- goto err_put_device;
-
if (nvmem->nkeepout) {
rval = nvmem_validate_keepouts(nvmem);
if (rval)
- goto err_device_del;
+ return ERR_PTR(rval);
}

if (config->compat) {
rval = nvmem_sysfs_setup_compat(nvmem, config);
if (rval)
- goto err_device_del;
+ return ERR_PTR(rval);
}

if (config->cells) {
@@ -867,19 +863,21 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
if (rval)
goto err_remove_cells;

+ rval = device_register(&nvmem->dev);
+ if (rval)
+ goto err_put_device;
+
blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);

return nvmem;

+err_put_device:
+ put_device(&nvmem->dev);
err_remove_cells:
nvmem_device_remove_all_cells(nvmem);
err_teardown_compat:
if (config->compat)
nvmem_sysfs_remove_compat(nvmem, config);
-err_device_del:
- device_del(&nvmem->dev);
-err_put_device:
- put_device(&nvmem->dev);

return ERR_PTR(rval);
}
--
2.35.1

2022-12-14 15:10:02

by Eric Curtin

Subject: Re: [PATCH] nvmem: core: Fix race in nvmem_register()

On Wed, 14 Dec 2022 at 14:40, Hector Martin <[email protected]> wrote:
>
> nvmem_register() currently registers the device before adding the nvmem
> cells, which creates a race window where consumers may find the nvmem
> device (and not get PROBE_DEFERred), but then fail to find the cells and
> error out.
>
> Move device registration to the end of nvmem_register(), to close the
> race.
>
> Observed when the stars line up on Apple Silicon machines with the (not
> yet upstream, but trivial) spmi nvmem driver and the macsmc-rtc client:
>
> [ 0.487375] macsmc-rtc macsmc-rtc: error -ENOENT: Failed to get rtc_offset NVMEM cell
>
> Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
> Signed-off-by: Hector Martin <[email protected]>

Reviewed-by: Eric Curtin <[email protected]>

> ---
> drivers/nvmem/core.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 321d7d63e068..d255feca5e17 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -837,20 +837,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>
> dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
>
> - rval = device_register(&nvmem->dev);
> - if (rval)
> - goto err_put_device;
> -
> if (nvmem->nkeepout) {
> rval = nvmem_validate_keepouts(nvmem);
> if (rval)
> - goto err_device_del;
> + return ERR_PTR(rval);
> }
>
> if (config->compat) {
> rval = nvmem_sysfs_setup_compat(nvmem, config);
> if (rval)
> - goto err_device_del;
> + return ERR_PTR(rval);
> }
>
> if (config->cells) {
> @@ -867,19 +863,21 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> if (rval)
> goto err_remove_cells;
>
> + rval = device_register(&nvmem->dev);
> + if (rval)
> + goto err_put_device;
> +
> blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
>
> return nvmem;
>
> +err_put_device:
> + put_device(&nvmem->dev);
> err_remove_cells:
> nvmem_device_remove_all_cells(nvmem);
> err_teardown_compat:
> if (config->compat)
> nvmem_sysfs_remove_compat(nvmem, config);
> -err_device_del:
> - device_del(&nvmem->dev);
> -err_put_device:
> - put_device(&nvmem->dev);
>
> return ERR_PTR(rval);
> }
> --
> 2.35.1
>
>

2023-01-03 11:41:01

by Srinivas Kandagatla

Subject: Re: [PATCH] nvmem: core: Fix race in nvmem_register()

Thanks Hector for the patch,


On 14/12/2022 14:29, Hector Martin wrote:
> nvmem_register() currently registers the device before adding the nvmem
> cells, which creates a race window where consumers may find the nvmem
> device (and not get PROBE_DEFERred), but then fail to find the cells and
> error out.
>
> Move device registration to the end of nvmem_register(), to close the
> race.
>
> Observed when the stars line up on Apple Silicon machines with the (not
> yet upstream, but trivial) spmi nvmem driver and the macsmc-rtc client:
>
> [ 0.487375] macsmc-rtc macsmc-rtc: error -ENOENT: Failed to get rtc_offset NVMEM cell
>
> Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
> Signed-off-by: Hector Martin <[email protected]>

Missing Cc Stable

> ---
> drivers/nvmem/core.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 321d7d63e068..d255feca5e17 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -837,20 +837,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>
> dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
>
> - rval = device_register(&nvmem->dev);
> - if (rval)
> - goto err_put_device;
> -
> if (nvmem->nkeepout) {
> rval = nvmem_validate_keepouts(nvmem);
> if (rval)
> - goto err_device_del;
> + return ERR_PTR(rval);

you can not do this as this will leak ida and nvmem itself.


> }
>
> if (config->compat) {
> rval = nvmem_sysfs_setup_compat(nvmem, config);
> if (rval)
> - goto err_device_del;
> + return ERR_PTR(rval);

same here.

> }
>
> if (config->cells) {
> @@ -867,19 +863,21 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> if (rval)
> goto err_remove_cells;
>
> + rval = device_register(&nvmem->dev);
> + if (rval)
> + goto err_put_device;
> +
> blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
>
> return nvmem;
>
> +err_put_device:
> + put_device(&nvmem->dev);

this will free nvmem and further down you are going to de-reference the
freed pointer.

--srini

> err_remove_cells:
> nvmem_device_remove_all_cells(nvmem);
> err_teardown_compat:
> if (config->compat)
> nvmem_sysfs_remove_compat(nvmem, config);
> -err_device_del:
> - device_del(&nvmem->dev);
> -err_put_device:
> - put_device(&nvmem->dev);
>
> return ERR_PTR(rval);
> }
> --
> 2.35.1
>