[PATCH v2 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

[PATCH v2 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

[Chen Jun]

An unexpected value of /proc/sys/vm/panic_on_oom we will get,
after running the following program.

int main()
{
    int fd = open("/proc/sys/vm/panic_on_oom", O_RDWR)
    write(fd, "1", 1);
    write(fd, "2", 1);
    close(fd);
}

write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
proc_dointvec_minmax will return 0 without setting new_policy.

t.data = &new_policy;
ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
      -->do_proc_dointvec
         -->__do_proc_dointvec
              if (write) {
                if (proc_first_pos_non_zero_ignore(ppos, table))
                  goto out;

sysctl_overcommit_memory = new_policy;

so sysctl_overcommit_memory will be set to an uninitialized value.

Check whether new_policy has been changed by proc_dointvec_minmax.

Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
Signed-off-by: Chen Jun <chenjun102@huawei.com>
---

v2:
  * Check whether new_policy has been changed by proc_dointvec_minmax.

 mm/util.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 4ddb6e186dd5..d5be67771850 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
 		size_t *lenp, loff_t *ppos)
 {
 	struct ctl_table t;
-	int new_policy;
+	int new_policy = -1;
 	int ret;
 
 	/*
@@ -774,7 +774,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
 		t = *table;
 		t.data = &new_policy;
 		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
-		if (ret)
+		if (ret || new_policy == -1)
 			return ret;
 
 		mm_compute_batch(new_policy);
-- 
2.17.1

Re: [PATCH v2 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

[Michal Hocko]

On Wed 22-09-21 01:41:22, Chen Jun wrote:
> An unexpected value of /proc/sys/vm/panic_on_oom we will get,
> after running the following program.
> 
> int main()
> {
>     int fd = open("/proc/sys/vm/panic_on_oom", O_RDWR)
>     write(fd, "1", 1);
>     write(fd, "2", 1);
>     close(fd);
> }
> 
> write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
> proc_dointvec_minmax will return 0 without setting new_policy.
> 
> t.data = &new_policy;
> ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
>       -->do_proc_dointvec
>          -->__do_proc_dointvec
>               if (write) {
>                 if (proc_first_pos_non_zero_ignore(ppos, table))
>                   goto out;
> 
> sysctl_overcommit_memory = new_policy;
> 
> so sysctl_overcommit_memory will be set to an uninitialized value.
> 
> Check whether new_policy has been changed by proc_dointvec_minmax.
> 
> Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
> Signed-off-by: Chen Jun <chenjun102@huawei.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Btw. you could also check for new_policy == sysctl_overcommit_memory so
that the sync of pcp counters is not fired without the policy change.
Something for a separate patch I guess.

> ---
> 
> v2:
>   * Check whether new_policy has been changed by proc_dointvec_minmax.
> 
>  mm/util.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 4ddb6e186dd5..d5be67771850 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>  		size_t *lenp, loff_t *ppos)
>  {
>  	struct ctl_table t;
> -	int new_policy;
> +	int new_policy = -1;
>  	int ret;
>  
>  	/*
> @@ -774,7 +774,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>  		t = *table;
>  		t.data = &new_policy;
>  		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
> -		if (ret)
> +		if (ret || new_policy == -1)
>  			return ret;
>  
>  		mm_compute_batch(new_policy);
> -- 
> 2.17.1

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v2 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

[Feng Tang]

Hi Jun,

On Wed, Sep 22, 2021 at 01:41:22AM +0000, Chen Jun wrote:
> An unexpected value of /proc/sys/vm/panic_on_oom we will get,
> after running the following program.
> 
> int main()
> {
>     int fd = open("/proc/sys/vm/panic_on_oom", O_RDWR)

should this be "/proc/sys/vm/overcommit_memory"

>     write(fd, "1", 1);
>     write(fd, "2", 1);
>     close(fd);
> }
> 
> write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
> proc_dointvec_minmax will return 0 without setting new_policy.
> 
> t.data = &new_policy;
> ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
>       -->do_proc_dointvec
>          -->__do_proc_dointvec
>               if (write) {
>                 if (proc_first_pos_non_zero_ignore(ppos, table))
>                   goto out;
> 
> sysctl_overcommit_memory = new_policy;
> 
> so sysctl_overcommit_memory will be set to an uninitialized value.
> 
> Check whether new_policy has been changed by proc_dointvec_minmax.
 
Other than the nit above, it looks good to me, thanks!

Reviewed-by: Feng Tang <feng.tang@intel.com>

> Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
> Signed-off-by: Chen Jun <chenjun102@huawei.com>
> ---
> 
> v2:
>   * Check whether new_policy has been changed by proc_dointvec_minmax.
> 
>  mm/util.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 4ddb6e186dd5..d5be67771850 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>  		size_t *lenp, loff_t *ppos)
>  {
>  	struct ctl_table t;
> -	int new_policy;
> +	int new_policy = -1;
>  	int ret;
>  
>  	/*
> @@ -774,7 +774,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>  		t = *table;
>  		t.data = &new_policy;
>  		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
> -		if (ret)
> +		if (ret || new_policy == -1)
>  			return ret;
>  
>  		mm_compute_batch(new_policy);
> -- 
> 2.17.1
> 

Re: [PATCH v2 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

[chenjun (AM)]

Hi Tang,

在 2021/9/22 23:34, Feng Tang 写道:
> Hi Jun,
> 
> On Wed, Sep 22, 2021 at 01:41:22AM +0000, Chen Jun wrote:
>> An unexpected value of /proc/sys/vm/panic_on_oom we will get,
>> after running the following program.
>>
>> int main()
>> {
>>      int fd = open("/proc/sys/vm/panic_on_oom", O_RDWR)
> 
> should this be "/proc/sys/vm/overcommit_memory"
> 

Sorry, that is my mistake, I will correct it in v3. Thanks.

>>      write(fd, "1", 1);
>>      write(fd, "2", 1);
>>      close(fd);
>> }
>>
>> write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
>> proc_dointvec_minmax will return 0 without setting new_policy.
>>
>> t.data = &new_policy;
>> ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
>>        -->do_proc_dointvec
>>           -->__do_proc_dointvec
>>                if (write) {
>>                  if (proc_first_pos_non_zero_ignore(ppos, table))
>>                    goto out;
>>
>> sysctl_overcommit_memory = new_policy;
>>
>> so sysctl_overcommit_memory will be set to an uninitialized value.
>>
>> Check whether new_policy has been changed by proc_dointvec_minmax.
>   
> Other than the nit above, it looks good to me, thanks!
> 
> Reviewed-by: Feng Tang <feng.tang@intel.com>
> 
>> Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
>> Signed-off-by: Chen Jun <chenjun102@huawei.com>
>> ---
>>
>> v2:
>>    * Check whether new_policy has been changed by proc_dointvec_minmax.
>>
>>   mm/util.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index 4ddb6e186dd5..d5be67771850 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>>   		size_t *lenp, loff_t *ppos)
>>   {
>>   	struct ctl_table t;
>> -	int new_policy;
>> +	int new_policy = -1;
>>   	int ret;
>>   
>>   	/*
>> @@ -774,7 +774,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
>>   		t = *table;
>>   		t.data = &new_policy;
>>   		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
>> -		if (ret)
>> +		if (ret || new_policy == -1)
>>   			return ret;
>>   
>>   		mm_compute_batch(new_policy);
>> -- 
>> 2.17.1
>>
> 


-- 
Regards
Chen Jun