2022-03-10 17:21:01

by Miaohe Lin

Subject: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So
the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix
this by resetting allowed to 0.

Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
Signed-off-by: Miaohe Lin <[email protected]>
---
mm/mlock.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/mm/mlock.c b/mm/mlock.c
index 29372c0eebe5..efd2dd2943de 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
}
if (!get_ucounts(ucounts)) {
dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
+ allowed = 0;
goto out;
}
allowed = 1;
--
2.23.0

2022-03-14 09:01:48

by Hugh Dickins

Subject: Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

On Mon, 14 Mar 2022, Miaohe Lin wrote:
> On 2022/3/14 10:40, Hugh Dickins wrote:
> > On Thu, 10 Mar 2022, Miaohe Lin wrote:
> >
> >> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So
> >> the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix
> >> this by resetting allowed to 0.
> >>
> >> Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
> >> Signed-off-by: Miaohe Lin <[email protected]>
> >
> > NAK. user_shm_lock() remembers to declare "int allowed = 0" on entry.
> >
>
> If lock_limit is RLIM_INFINITY, "allowed" will be set to 1. And if get_ucounts fails
> in some corner cases, "allowed" will remain to be 1 while the user_shm_lock ops indeed
> fails. Or am I miss something?

You are right, I am wrong: sorry.
Thanks for pointing now to that RLIM_INFINITY case.

But then the Fixes tag is wrong: it should be
Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
which introduced the possibility of error down there.

With that,
Acked-by: Hugh Dickins <[email protected]>

>
> Many thanks for comment.
>
> >> ---
> >> mm/mlock.c | 1 +
> >> 1 file changed, 1 insertion(+)
> >>
> >> diff --git a/mm/mlock.c b/mm/mlock.c
> >> index 29372c0eebe5..efd2dd2943de 100644
> >> --- a/mm/mlock.c
> >> +++ b/mm/mlock.c
> >> @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
> >> }
> >> if (!get_ucounts(ucounts)) {
> >> dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
> >> + allowed = 0;
> >> goto out;
> >> }
> >> allowed = 1;
> >> --
> >> 2.23.0

2022-03-14 12:11:31

by Hugh Dickins

Subject: Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

On Thu, 10 Mar 2022, Miaohe Lin wrote:

> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So
> the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix
> this by resetting allowed to 0.
>
> Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
> Signed-off-by: Miaohe Lin <[email protected]>

NAK. user_shm_lock() remembers to declare "int allowed = 0" on entry.

> ---
> mm/mlock.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 29372c0eebe5..efd2dd2943de 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
> }
> if (!get_ucounts(ucounts)) {
> dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
> + allowed = 0;
> goto out;
> }
> allowed = 1;
> --
> 2.23.0
>
>
>

2022-03-14 13:39:15

by Miaohe Lin

Subject: Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

On 2022/3/14 10:40, Hugh Dickins wrote:
> On Thu, 10 Mar 2022, Miaohe Lin wrote:
>
>> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So
>> the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix
>> this by resetting allowed to 0.
>>
>> Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
>> Signed-off-by: Miaohe Lin <[email protected]>
>
> NAK. user_shm_lock() remembers to declare "int allowed = 0" on entry.
>

If lock_limit is RLIM_INFINITY, "allowed" will be set to 1. And if get_ucounts fails
in some corner cases, "allowed" will remain to be 1 while the user_shm_lock ops indeed
fails. Or am I miss something?

Many thanks for comment.

>> ---
>> mm/mlock.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/mlock.c b/mm/mlock.c
>> index 29372c0eebe5..efd2dd2943de 100644
>> --- a/mm/mlock.c
>> +++ b/mm/mlock.c
>> @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
>> }
>> if (!get_ucounts(ucounts)) {
>> dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
>> + allowed = 0;
>> goto out;
>> }
>> allowed = 1;
>> --
>> 2.23.0
>>
>>
>>
> .
>

2022-03-15 18:15:36

by Miaohe Lin

Subject: Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

On 2022/3/14 11:11, Hugh Dickins wrote:
> On Mon, 14 Mar 2022, Miaohe Lin wrote:
>> On 2022/3/14 10:40, Hugh Dickins wrote:
>>> On Thu, 10 Mar 2022, Miaohe Lin wrote:
>>>
>>>> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So
>>>> the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix
>>>> this by resetting allowed to 0.
>>>>
>>>> Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
>>>> Signed-off-by: Miaohe Lin <[email protected]>
>>>
>>> NAK. user_shm_lock() remembers to declare "int allowed = 0" on entry.
>>>
>>
>> If lock_limit is RLIM_INFINITY, "allowed" will be set to 1. And if get_ucounts fails
>> in some corner cases, "allowed" will remain to be 1 while the user_shm_lock ops indeed
>> fails. Or am I miss something?
>
> You are right, I am wrong: sorry.
> Thanks for pointing now to that RLIM_INFINITY case.
>
> But then the Fixes tag is wrong: it should be
> Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
> which introduced the possibility of error down there.
>

You're right. commit 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
introduced RLIM_INFINITY and set "allowed" to 1 but there is no possibility of error down there.
Will change this in V2.

> With that,
> Acked-by: Hugh Dickins <[email protected]>

Many thanks!

>
>>
>> Many thanks for comment.
>>
>>>> ---
>>>> mm/mlock.c | 1 +
>>>> 1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/mm/mlock.c b/mm/mlock.c
>>>> index 29372c0eebe5..efd2dd2943de 100644
>>>> --- a/mm/mlock.c
>>>> +++ b/mm/mlock.c
>>>> @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
>>>> }
>>>> if (!get_ucounts(ucounts)) {
>>>> dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
>>>> + allowed = 0;
>>>> goto out;
>>>> }
>>>> allowed = 1;
>>>> --
>>>> 2.23.0
> .
>