diff mbox series

mmc: dw_mmc: Fix potential null pointer risk

Message ID 20240307085135.16245-1-amishin@t-argos.ru
State New
Headers show
Series mmc: dw_mmc: Fix potential null pointer risk | expand

Commit Message

Aleksandr Mishin March 7, 2024, 8:51 a.m. UTC
In dw_mci_runtime_resume() 'host->slot' could be null, but check is not cover all corresponding code.
Fix this bug by changing check place.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 4a835afd808a (mmc: dw_mmc: Fix potential null pointer risk)
Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
---
 drivers/mmc/host/dw_mmc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Aleksandr Mishin March 7, 2024, 7:02 p.m. UTC | #1
07.03.2024 13:57, Ulf Hansson wrote:
> On Thu, 7 Mar 2024 at 09:53, Aleksandr Mishin <amishin@t-argos.ru> wrote:
>>
>> In dw_mci_runtime_resume() 'host->slot' could be null, but check is not cover all corresponding code.
>> Fix this bug by changing check place.
> 
> In fact host->slot can never be NULL in dw_mci_runtime_resume() or in
> dw_mci_runtime_suspend().
> 
> A better fix would thus be to remove the redundant checks.
> 
> Kind regards
> Uffe
> 
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Fixes: 4a835afd808a (mmc: dw_mmc: Fix potential null pointer risk)
>> Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
>> ---
>>   drivers/mmc/host/dw_mmc.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index 829af2c98a44..a4f124452abc 100644
>> --- a/drivers/mmc/host/dw_mmc.c
>> +++ b/drivers/mmc/host/dw_mmc.c
>> @@ -3570,8 +3570,10 @@ int dw_mci_runtime_resume(struct device *dev)
>>                     DW_MCI_ERROR_FLAGS);
>>          mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
>>
>> +       if (!host->slot)
>> +               goto err;
>>
>> -       if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
>> +       if (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 */
>> --
>> 2.30.2
>>
>>
> 

At the same time there are few checks such as "if (host->slot)" in 
dw_mci_runtime_resume() and commit 
4a835afd808a3dbbac44bb399a902b822dc7445c message contains: "we 
previously assumed 'host->slot' could be null, null pointer judgment 
should be added" and replaces "if (host->slot->mmc->pm_flags & 
MMC_PM_KEEP_POWER)" with "if (host->slot && host->slot->mmc->pm_flags & 
MMC_PM_KEEP_POWER)"
So where is the truth?
Ulf Hansson March 12, 2024, 11:29 a.m. UTC | #2
On Thu, 7 Mar 2024 at 20:07, Aleksandr Mishin <amishin@t-argos.ru> wrote:
>
>
>
> 07.03.2024 13:57, Ulf Hansson wrote:
> > On Thu, 7 Mar 2024 at 09:53, Aleksandr Mishin <amishin@t-argos.ru> wrote:
> >>
> >> In dw_mci_runtime_resume() 'host->slot' could be null, but check is not cover all corresponding code.
> >> Fix this bug by changing check place.
> >
> > In fact host->slot can never be NULL in dw_mci_runtime_resume() or in
> > dw_mci_runtime_suspend().
> >
> > A better fix would thus be to remove the redundant checks.
> >
> > Kind regards
> > Uffe
> >
> >>
> >> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >>
> >> Fixes: 4a835afd808a (mmc: dw_mmc: Fix potential null pointer risk)
> >> Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
> >> ---
> >>   drivers/mmc/host/dw_mmc.c | 4 +++-
> >>   1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> >> index 829af2c98a44..a4f124452abc 100644
> >> --- a/drivers/mmc/host/dw_mmc.c
> >> +++ b/drivers/mmc/host/dw_mmc.c
> >> @@ -3570,8 +3570,10 @@ int dw_mci_runtime_resume(struct device *dev)
> >>                     DW_MCI_ERROR_FLAGS);
> >>          mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
> >>
> >> +       if (!host->slot)
> >> +               goto err;
> >>
> >> -       if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> >> +       if (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 */
> >> --
> >> 2.30.2
> >>
> >>
> >
>
> At the same time there are few checks such as "if (host->slot)" in
> dw_mci_runtime_resume() and commit
> 4a835afd808a3dbbac44bb399a902b822dc7445c message contains: "we
> previously assumed 'host->slot' could be null, null pointer judgment
> should be added" and replaces "if (host->slot->mmc->pm_flags &
> MMC_PM_KEEP_POWER)" with "if (host->slot && host->slot->mmc->pm_flags &
> MMC_PM_KEEP_POWER)"
> So where is the truth?

It looks to me that the runtime PM callbacks are prevented from being
called, unless we have a host->slot assigned.

Just adding checks because it looks like the code could need it, isn't
always the correct thing to do. I would rather try to remove the
checks altogether and give it some tests to see how it plays.

Kind regards
Uffe
diff mbox series

Patch

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 829af2c98a44..a4f124452abc 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -3570,8 +3570,10 @@  int dw_mci_runtime_resume(struct device *dev)
 		   DW_MCI_ERROR_FLAGS);
 	mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
 
+	if (!host->slot)
+		goto err;
 
-	if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
+	if (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 */