On Wed, Apr 13, 2022 at 10:54:27AM +0200, Alessandro Astone wrote:
> When handling BINDER_TYPE_FDA object we are pushing a parent fixup
> with a certain skip_size but no scatter-gather copy object, since
> the copy is handled standalone.
> If BINDER_TYPE_FDA is the last children the scatter-gather copy
> loop will never stop to skip it, thus we are left with an item in
> the parent fixup list. This will trigger the BUG_ON().
>
> Furthermore, it is possible to receive BINDER_TYPE_FDA object
> with num_fds=0 which will confuse the scatter-gather code.
>
> In the android userspace I could only find these usecases in the
> libstagefright OMX implementation, so it might be that they're
> doing something very weird, but nonetheless the kernel should not
> panic about it.
>
> Fixes: 09184ae9b575 ("binder: defer copies of pre-patched txn data")
> Signed-off-by: Alessandro Astone <[email protected]>
> ---
> drivers/android/binder.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 8351c5638880..18ad6825ba30 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -2295,7 +2295,7 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
> {
> int ret = 0;
> struct binder_sg_copy *sgc, *tmpsgc;
> - struct binder_ptr_fixup *pf =
> + struct binder_ptr_fixup *tmppf, *pf =
Just make this a new line:
struct binder_ptr_fixup *tmppf;
above the existing line.
> list_first_entry_or_null(pf_head, struct binder_ptr_fixup,
> node);
>
> @@ -2349,7 +2349,11 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
> list_del(&sgc->node);
> kfree(sgc);
> }
> - BUG_ON(!list_empty(pf_head));
So you are hitting this BUG_ON() today?
> + list_for_each_entry_safe(pf, tmppf, pf_head, node) {
> + BUG_ON(pf->skip_size == 0);
> + list_del(&pf->node);
> + kfree(pf);
> + }
> BUG_ON(!list_empty(sgc_head));
>
> return ret > 0 ? -EINVAL : ret;
> @@ -2486,6 +2490,9 @@ static int binder_translate_fd_array(struct list_head *pf_head,
> struct binder_proc *proc = thread->proc;
> int ret;
>
> + if (fda->num_fds == 0)
> + return 0;
Why return 0?
This feels like a separate issue from above, should this be 2 different
commits?
thanks,
greg k-h
On 13/04/2022 12:00, Greg KH wrote:
> On Wed, Apr 13, 2022 at 10:54:27AM +0200, Alessandro Astone wrote:
>> When handling BINDER_TYPE_FDA object we are pushing a parent fixup
>> with a certain skip_size but no scatter-gather copy object, since
>> the copy is handled standalone.
>> If BINDER_TYPE_FDA is the last children the scatter-gather copy
>> loop will never stop to skip it, thus we are left with an item in
>> the parent fixup list. This will trigger the BUG_ON().
>>
>> Furthermore, it is possible to receive BINDER_TYPE_FDA object
>> with num_fds=0 which will confuse the scatter-gather code.
>>
>> In the android userspace I could only find these usecases in the
>> libstagefright OMX implementation, so it might be that they're
>> doing something very weird, but nonetheless the kernel should not
>> panic about it.
>>
>> Fixes: 09184ae9b575 ("binder: defer copies of pre-patched txn data")
>> Signed-off-by: Alessandro Astone <[email protected]>
>> ---
>> drivers/android/binder.c | 11 +++++++++--
>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
>> index 8351c5638880..18ad6825ba30 100644
>> --- a/drivers/android/binder.c
>> +++ b/drivers/android/binder.c
>> @@ -2295,7 +2295,7 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
>> {
>> int ret = 0;
>> struct binder_sg_copy *sgc, *tmpsgc;
>> - struct binder_ptr_fixup *pf =
>> + struct binder_ptr_fixup *tmppf, *pf =
> Just make this a new line:
> struct binder_ptr_fixup *tmppf;
> above the existing line.
>
Ack.
>> list_first_entry_or_null(pf_head, struct binder_ptr_fixup,
>> node);
>>
>> @@ -2349,7 +2349,11 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
>> list_del(&sgc->node);
>> kfree(sgc);
>> }
>> - BUG_ON(!list_empty(pf_head));
> So you are hitting this BUG_ON() today?
>
Correct, both on 5.17, stable 5.17.2 and current master
>> + list_for_each_entry_safe(pf, tmppf, pf_head, node) {
>> + BUG_ON(pf->skip_size == 0);
>> + list_del(&pf->node);
>> + kfree(pf);
>> + }
>> BUG_ON(!list_empty(sgc_head));
>>
>> return ret > 0 ? -EINVAL : ret;
>> @@ -2486,6 +2490,9 @@ static int binder_translate_fd_array(struct list_head *pf_head,
>> struct binder_proc *proc = thread->proc;
>> int ret;
>>
>> + if (fda->num_fds == 0)
>> + return 0;
> Why return 0?
>
> This feels like a separate issue from above, should this be 2 different
> commits?
>
return 0 because I want it to be handled as it was handled before
09184ae9b575 ("binder: defer copies of pre-patched txn data")
Function `binder_do_deferred_txn_copies` distinguishes between a copy-fixup
and a skip with `if (pf->skip_size)` so if the skip_size is 0, which happens
if fda->num_fds is 0, it would accidentally enter the wrong branch.
By returning 0 early i make sure a skip of size 0 is not added. It's not an
error because it was never an error before commit 09184ae9b575 and some
userspace in android is hitting this path.
I would agree it's a separate issue.
I originally merged it in this same patch because
1) Both are fixups to 09184ae9b575
2) Both are triggered by the same real-world android transaction that looks
something like this:
obj[0] BINDER_TYPE_PTR, parent
obj[1] BINDER_TYPE_PTR, child
obj[2] BINDER_TYPE_PTR, child
obj[3] BINDER_TYPE_FDA with num_fds=0
3) In the other hunk of this patch i replace the BUG_ON with:
BUG_ON(pf->skip_size == 0)
to only BUG if any item remaining in the pf_head list is not a skip,
but as observed we may receive skips of size 0.
4) With this hunk only, you would no longer reproduce the BUG_ON because the
only transaction we receive in android with BINDER_TYPE_FDA as last child
coincidentally always has num_fds=0. Certainly some weird behaviour...
So if I split them, patch A would depend on patch B (see point 3), but the
BUG of patch B would only be reproducible without patch A (see point 4).
But let me know if you still prefer them split.
> thanks,
>
> greg k-h
On Wed, Apr 13, 2022 at 4:20 AM Alessandro Astone <[email protected]> wrote:
>
> On 13/04/2022 12:00, Greg KH wrote:
>
> > On Wed, Apr 13, 2022 at 10:54:27AM +0200, Alessandro Astone wrote:
> >> When handling BINDER_TYPE_FDA object we are pushing a parent fixup
> >> with a certain skip_size but no scatter-gather copy object, since
> >> the copy is handled standalone.
> >> If BINDER_TYPE_FDA is the last children the scatter-gather copy
> >> loop will never stop to skip it, thus we are left with an item in
> >> the parent fixup list. This will trigger the BUG_ON().
> >>
> >> Furthermore, it is possible to receive BINDER_TYPE_FDA object
> >> with num_fds=0 which will confuse the scatter-gather code.
> >>
> >> In the android userspace I could only find these usecases in the
> >> libstagefright OMX implementation, so it might be that they're
> >> doing something very weird, but nonetheless the kernel should not
> >> panic about it.
> >>
> >> Fixes: 09184ae9b575 ("binder: defer copies of pre-patched txn data")
> >> Signed-off-by: Alessandro Astone <[email protected]>
> >> ---
> >> drivers/android/binder.c | 11 +++++++++--
> >> 1 file changed, 9 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> >> index 8351c5638880..18ad6825ba30 100644
> >> --- a/drivers/android/binder.c
> >> +++ b/drivers/android/binder.c
> >> @@ -2295,7 +2295,7 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
> >> {
> >> int ret = 0;
> >> struct binder_sg_copy *sgc, *tmpsgc;
> >> - struct binder_ptr_fixup *pf =
> >> + struct binder_ptr_fixup *tmppf, *pf =
> > Just make this a new line:
> > struct binder_ptr_fixup *tmppf;
> > above the existing line.
> >
> Ack.
>
> >> list_first_entry_or_null(pf_head, struct binder_ptr_fixup,
> >> node);
> >>
> >> @@ -2349,7 +2349,11 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
> >> list_del(&sgc->node);
> >> kfree(sgc);
> >> }
> >> - BUG_ON(!list_empty(pf_head));
> > So you are hitting this BUG_ON() today?
> >
> Correct, both on 5.17, stable 5.17.2 and current master
>
> >> + list_for_each_entry_safe(pf, tmppf, pf_head, node) {
> >> + BUG_ON(pf->skip_size == 0);
> >> + list_del(&pf->node);
> >> + kfree(pf);
> >> + }
> >> BUG_ON(!list_empty(sgc_head));
> >>
> >> return ret > 0 ? -EINVAL : ret;
> >> @@ -2486,6 +2490,9 @@ static int binder_translate_fd_array(struct list_head *pf_head,
> >> struct binder_proc *proc = thread->proc;
> >> int ret;
> >>
> >> + if (fda->num_fds == 0)
> >> + return 0;
> > Why return 0?
> >
> > This feels like a separate issue from above, should this be 2 different
> > commits?
> >
> return 0 because I want it to be handled as it was handled before
> 09184ae9b575 ("binder: defer copies of pre-patched txn data")
>
> Function `binder_do_deferred_txn_copies` distinguishes between a copy-fixup
> and a skip with `if (pf->skip_size)` so if the skip_size is 0, which happens
> if fda->num_fds is 0, it would accidentally enter the wrong branch.
> By returning 0 early i make sure a skip of size 0 is not added. It's not an
> error because it was never an error before commit 09184ae9b575 and some
> userspace in android is hitting this path.
>
> I would agree it's a separate issue.
> I originally merged it in this same patch because
> 1) Both are fixups to 09184ae9b575
> 2) Both are triggered by the same real-world android transaction that looks
> something like this:
> obj[0] BINDER_TYPE_PTR, parent
> obj[1] BINDER_TYPE_PTR, child
> obj[2] BINDER_TYPE_PTR, child
> obj[3] BINDER_TYPE_FDA with num_fds=0
> 3) In the other hunk of this patch i replace the BUG_ON with:
> BUG_ON(pf->skip_size == 0)
> to only BUG if any item remaining in the pf_head list is not a skip,
> but as observed we may receive skips of size 0.
> 4) With this hunk only, you would no longer reproduce the BUG_ON because the
> only transaction we receive in android with BINDER_TYPE_FDA as last child
> coincidentally always has num_fds=0. Certainly some weird behaviour...
>
> So if I split them, patch A would depend on patch B (see point 3), but the
> BUG of patch B would only be reproducible without patch A (see point 4).
>
> But let me know if you still prefer them split.
Thanks for the fix! Please go ahead and split it into two patches.
>
> > thanks,
> >
> > greg k-h