2019-07-26 14:24:36

by Jia-Ju Bai

Subject: [PATCH] mmc: host: dw_mmc: Fix possible null-pointer dereferences in dw_mci_runtime_resume()

In dw_mci_runtime_resume(), there is an if statement on line 3420
to check whether host->slot is NULL:
if (host->slot && ...)

When host->slot is NULL, it is used on line 3458:
if (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
and on line 3462:
dw_mci_setup_bus(host->slot, true);
struct dw_mci *host = slot->host;

Thus, possible null-pointer dereferences may occur.

To fix these bugs, host->slot is checked before being used.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
drivers/mmc/host/dw_mmc.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index faaaf52a46d2..91bd6c3ccf50 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -3455,11 +3455,12 @@ int dw_mci_runtime_resume(struct device *dev)
mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);


- if (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
+ if (host->slot && (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER))
dw_mci_set_ios(host->slot->mmc, &host->slot->mmc->ios);

/* Force setup bus to guarantee available clock output */
- dw_mci_setup_bus(host->slot, true);
+ if (host->slot)
+ dw_mci_setup_bus(host->slot, true);

/* Now that slots are all setup, we can enable card detect */
dw_mci_enable_cd(host);
--
2.17.0

2019-08-01 15:46:46

by Ulf Hansson

Subject: Re: [PATCH] mmc: host: dw_mmc: Fix possible null-pointer dereferences in dw_mci_runtime_resume()

On Fri, 26 Jul 2019 at 16:23, Jia-Ju Bai <[email protected]> wrote:
>
> In dw_mci_runtime_resume(), there is an if statement on line 3420
> to check whether host->slot is NULL:
> if (host->slot && ...)
>
> When host->slot is NULL, it is used on line 3458:
> if (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> and on line 3462:
> dw_mci_setup_bus(host->slot, true);
> struct dw_mci *host = slot->host;
>
> Thus, possible null-pointer dereferences may occur.
>
> To fix these bugs, host->slot is checked before being used.
>
> These bugs are found by a static analysis tool STCheck written by us.

I fully respect these kind of tools and they for sure find lots of
problems for us.

However, in this case I think the fix should be made a bit
differently, see more below.

>
> Signed-off-by: Jia-Ju Bai <[email protected]>
> ---
> drivers/mmc/host/dw_mmc.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index faaaf52a46d2..91bd6c3ccf50 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -3455,11 +3455,12 @@ int dw_mci_runtime_resume(struct device *dev)
> mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
>
>
> - if (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> + if (host->slot && (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER))
> dw_mci_set_ios(host->slot->mmc, &host->slot->mmc->ios);

Unless I missing something (still in "slow mode" due to holidays),
dw_mci_runtime_suspend|resume() should only be called when there is a
slot (host->slot) initialized for the host. This is guaranteed by the
the driver when it runs ->probe().

>
> /* Force setup bus to guarantee available clock output */
> - dw_mci_setup_bus(host->slot, true);
> + if (host->slot)
> + dw_mci_setup_bus(host->slot, true);

Ditto.

>
> /* Now that slots are all setup, we can enable card detect */
> dw_mci_enable_cd(host);

So, I am thinking that there is really no need to check for host->slot
at all. And if there really were, I am sure there would have been bug
reports already about it.

Kind regards
Uffe