* copy_mount_options() problem
@ 2019-10-15 15:12 Pavel V. Panteleev
0 siblings, 0 replies; 6+ messages in thread
From: Pavel V. Panteleev @ 2019-10-15 15:12 UTC (permalink / raw)
To: linux-fsdevel
Hello,
copy_mount_options() checks that data doesn' cross TASK_SIZE boundary. It's not correct. Really it should check USER_DS boudary, because some archs have TASK_SIZE not equal to USER_DS. In this case (USER_DS != TASK_SIZE) exact_copy_from_user() will stop on access_ok() check, if data cross USER_DS, but doesn't cross TASK_SIZE.
Best regards,
Pavel V. Panteleev
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: copy_mount_options() problem
2019-10-15 22:03 ` Al Viro
@ 2019-10-16 7:39 ` Pavel V. Panteleev
0 siblings, 0 replies; 6+ messages in thread
From: Pavel V. Panteleev @ 2019-10-16 7:39 UTC (permalink / raw)
To: Al Viro; +Cc: linux-fsdevel
This works, thanks.
On 16.10.2019 01:03, Al Viro wrote:
> On Tue, Oct 15, 2019 at 07:40:34PM +0100, Al Viro wrote:
>> On Tue, Oct 15, 2019 at 09:09:02PM +0300, Pavel V. Panteleev wrote:
>>> Hello,
>>>
>>> copy_mount_options() checks that data doesn't cross TASK_SIZE boundary. It's
>>> not correct. Really it should check USER_DS boudary, because some archs have
>>> TASK_SIZE not equal to USER_DS. In this case (USER_DS != TASK_SIZE)
>>> exact_copy_from_user() will stop on access_ok() check, if data cross
>>> USER_DS, but doesn't cross TASK_SIZE.
>> Details of the call chain, please.
> FWIW, what I want to do with copy_mount_options() is this:
> void *copy_mount_options(const void __user * data)
> {
> unsigned offs, size;
> char *copy;
>
> if (!data)
> return NULL;
>
> copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
> if (!copy)
> return ERR_PTR(-ENOMEM);
>
> offs = (unsigned long)data & (PAGE_SIZE - 1);
>
> if (copy_from_user(copy, data, PAGE_SIZE - offs)) {
> kfree(copy);
> return ERR_PTR(-EFAULT);
> }
> if (offs) {
> if (copy_from_user(copy, data + PAGE_SIZE - offs, offs))
> memset(copy + PAGE_SIZE - offs, 0, offs);
> }
> return copy;
> }
>
> which should get rid of any TASK_SIZE references whatsoever, but I really
> wonder where have you run into the problem.
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: copy_mount_options() problem
2019-10-15 18:40 ` Al Viro
2019-10-15 22:03 ` Al Viro
@ 2019-10-16 7:31 ` Pavel V. Panteleev
1 sibling, 0 replies; 6+ messages in thread
From: Pavel V. Panteleev @ 2019-10-16 7:31 UTC (permalink / raw)
To: Al Viro; +Cc: linux-fsdevel
# tracer: nop
#
# entries-in-buffer/entries-written: 3/3 #P:16
#
# _-----=> irqs-off
# / _----=> need-resched
# |/ _-----=> need-resched_lazy
# || / _---=> hardirq/softirq
# ||| / _--=> preempt-depth
# |||| / _-=> preempt-lazy-depth
# ||||| / _-=> migrate-disable
# |||||| / delay
# TASK-PID CPU# ||||||| TIMESTAMP FUNCTION
# | | | ||||||| | |
automount-5999 [001] ....... 170.320000: 0:
copy_mount_options(): copy 0xd017d560b000 data 0xc2dfffffe340 size
0x1000 USER_DS 0xc2dffffff000 TASK_SIZE 0xd00000000000
automount-5999 [001] ....... 170.320000: :
exact_copy_from_user(): !access_ok
automount-5999 [001] ....... 170.320000: :
copy_mount_options(): return -EFAULT
On 15.10.2019 21:40, Al Viro wrote:
> On Tue, Oct 15, 2019 at 09:09:02PM +0300, Pavel V. Panteleev wrote:
>> Hello,
>>
>> copy_mount_options() checks that data doesn't cross TASK_SIZE boundary. It's
>> not correct. Really it should check USER_DS boudary, because some archs have
>> TASK_SIZE not equal to USER_DS. In this case (USER_DS != TASK_SIZE)
>> exact_copy_from_user() will stop on access_ok() check, if data cross
>> USER_DS, but doesn't cross TASK_SIZE.
> Details of the call chain, please.
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: copy_mount_options() problem
2019-10-15 18:40 ` Al Viro
@ 2019-10-15 22:03 ` Al Viro
2019-10-16 7:39 ` Pavel V. Panteleev
2019-10-16 7:31 ` Pavel V. Panteleev
1 sibling, 1 reply; 6+ messages in thread
From: Al Viro @ 2019-10-15 22:03 UTC (permalink / raw)
To: Pavel V. Panteleev; +Cc: linux-fsdevel
On Tue, Oct 15, 2019 at 07:40:34PM +0100, Al Viro wrote:
> On Tue, Oct 15, 2019 at 09:09:02PM +0300, Pavel V. Panteleev wrote:
> > Hello,
> >
> > copy_mount_options() checks that data doesn't cross TASK_SIZE boundary. It's
> > not correct. Really it should check USER_DS boudary, because some archs have
> > TASK_SIZE not equal to USER_DS. In this case (USER_DS != TASK_SIZE)
> > exact_copy_from_user() will stop on access_ok() check, if data cross
> > USER_DS, but doesn't cross TASK_SIZE.
>
> Details of the call chain, please.
FWIW, what I want to do with copy_mount_options() is this:
void *copy_mount_options(const void __user * data)
{
unsigned offs, size;
char *copy;
if (!data)
return NULL;
copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!copy)
return ERR_PTR(-ENOMEM);
offs = (unsigned long)data & (PAGE_SIZE - 1);
if (copy_from_user(copy, data, PAGE_SIZE - offs)) {
kfree(copy);
return ERR_PTR(-EFAULT);
}
if (offs) {
if (copy_from_user(copy, data + PAGE_SIZE - offs, offs))
memset(copy + PAGE_SIZE - offs, 0, offs);
}
return copy;
}
which should get rid of any TASK_SIZE references whatsoever, but I really
wonder where have you run into the problem.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: copy_mount_options() problem
2019-10-15 18:09 Pavel V. Panteleev
@ 2019-10-15 18:40 ` Al Viro
2019-10-15 22:03 ` Al Viro
2019-10-16 7:31 ` Pavel V. Panteleev
0 siblings, 2 replies; 6+ messages in thread
From: Al Viro @ 2019-10-15 18:40 UTC (permalink / raw)
To: Pavel V. Panteleev; +Cc: linux-fsdevel
On Tue, Oct 15, 2019 at 09:09:02PM +0300, Pavel V. Panteleev wrote:
> Hello,
>
> copy_mount_options() checks that data doesn't cross TASK_SIZE boundary. It's
> not correct. Really it should check USER_DS boudary, because some archs have
> TASK_SIZE not equal to USER_DS. In this case (USER_DS != TASK_SIZE)
> exact_copy_from_user() will stop on access_ok() check, if data cross
> USER_DS, but doesn't cross TASK_SIZE.
Details of the call chain, please.
^ permalink raw reply [flat|nested] 6+ messages in thread
* copy_mount_options() problem
@ 2019-10-15 18:09 Pavel V. Panteleev
2019-10-15 18:40 ` Al Viro
0 siblings, 1 reply; 6+ messages in thread
From: Pavel V. Panteleev @ 2019-10-15 18:09 UTC (permalink / raw)
To: linux-fsdevel
Hello,
copy_mount_options() checks that data doesn't cross TASK_SIZE boundary.
It's not correct. Really it should check USER_DS boudary, because some
archs have TASK_SIZE not equal to USER_DS. In this case (USER_DS !=
TASK_SIZE) exact_copy_from_user() will stop on access_ok() check, if
data cross USER_DS, but doesn't cross TASK_SIZE.
Best regards,
Pavel V. Panteleev
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-10-16 7:40 UTC | newest]
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2019-10-15 15:12 copy_mount_options() problem Pavel V. Panteleev
2019-10-15 18:09 Pavel V. Panteleev
2019-10-15 18:40 ` Al Viro
2019-10-15 22:03 ` Al Viro
2019-10-16 7:39 ` Pavel V. Panteleev
2019-10-16 7:31 ` Pavel V. Panteleev
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