Re: Re: WARNING in input_alloc_absinfo

[syzbot]

> On Thu, Jul 26, 2018 at 11:40 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx>  
> wrote:
> > On Mon, Jul 2, 2018 at 11:30 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx>  
> > wrote:
> > > On Fri, Jun 29, 2018 at 11:59 PM,  <dmitry.torokhov@xxxxxxxxx> wrote:
> > > > On Monday, June 25, 2018 at 5:43:02 AM UTC-7, Dmitry Vyukov wrote:

> > > > > On Tue, Jun 19, 2018 at 8:51 PM, Dmitry Torokhov
> > > > > <dmitry....@xxxxxxxxx> wrote:
> > > > > > On Thu, Jun 14, 2018 at 05:47:03AM -0700, syzbot wrote:
> > > > > >> Hello,
> > > > > >>
> > > > > >> syzbot found the following crash on:
> > > > > >>
> > > > > >> HEAD commit:    d2d741e5d189 kmsan: add initialization for shmem  
> > > > > pages
> > > > > >> git tree:       https://github.com/google/kmsan.git/master
> > > > > >> console output:
> > > > > >> https://syzkaller.appspot.com/x/log.txt?x=1775bae7800000
> > > > > >> kernel config:
> > > > > >> https://syzkaller.appspot.com/x/.config?x=48f9de3384bcd0f
> > > > > >> dashboard link:
> > > > > >> https://syzkaller.appspot.com/bug?extid=c382812c78d98ecd9fb8
> > > > > >> compiler:       clang version 7.0.0 (trunk 329391)
> > > > > >> syzkaller
> > > > > >> repro:https://syzkaller.appspot.com/x/repro.syz?x=13b31ae7800000
> > > > > >> C reproducer:
> > > > > >> https://syzkaller.appspot.com/x/repro.c?x=1733255b800000
> > > > > >>
> > > > > >> IMPORTANT: if you fix the bug, please add the following tag to the
> > > > > >> commit:
> > > > > >> Reported-by: syzbot+c38281...@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > > >>
> > > > > >> RBP: 00000000006cb018 R08: 0000000000000001 R09: 00007ffe93080031
> > > > > >> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
> > > > > >> R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
> > > > > >> ------------[ cut here ]------------
> > > > > >> input_alloc_absinfo(): kcalloc() failed?
> > > > > >> WARNING: CPU: 1 PID: 4498 at drivers/input/input.c:487
> > > > > >> input_alloc_absinfo+0x183/0x190 drivers/input/input.c:487
> > > > > >> Kernel panic - not syncing: panic_on_warn set ...
> > > > > >
> > > > > > Hmm, so there is not really a problem as far as I am concerned. We  
> > > > > do
> > > > > > generate a warning if we can't allocate memory for absinfo,  as  
> > > > > this is
> > > > > > really unexpected, but the case is handled properly by the callers  
> > > > > so
> > > > > > there is no reason for us to go belly up here.

> > > > > Note to myself: ping this bug when "include/asm-generic/bug.h: clarify
> > > > > valid uses of WARN()" is fully merged.


> > > > No, this warning will still be there even after the "clarifying" patch  
> > > > is
> > > > merged. It does not check user inputs, it warns that the system is so  
> > > > low on
> > > > memory that we could not allocate measly amount needed for absinfo.  
> > > > Treat it
> > > > as you treat OOM warnings from kmalloc() itself.

> > > Hi Dmitry,

> > > kmalloc does not produce WARNING on OOM. The rule is not only about
> > > invalid inputs, it's also about any transient conditions and "WARNING
> > > only for kernel bugs".

> > > To put this in larger context, being able to distinguish kernel bugs
> > > from non-bugs is a very important and practically useful capability,
> > > which in particular enables systematic testing, but also makes things
> > > simpler for all kernel users. There must be a very significant reason
> > > to abandon this capability. What is that reason in this case?

> > > I also don't understand what is so special about this case. If we want
> > > user message for kmalloc failures, kmalloc is the right place for such
> > > warning, rather than a random call site out of thousands. Consider,
> > > the allocation failure can happen on the very next or previous kmalloc
> > > call, and user won't be warned. The rest of the kernel (including the
> > > rest of input sybsystem) does not warn on allocation failures, so that
> > > looks like what we need to do here as well. Or, if there is something
> > > very special about this particular kmalloc call site, something that
> > > makes it different from thousands of other call sites, why don't you
> > > want to replace it with pr_err which would both give the diagnostics
> > > but also not block systematic testing? Which looks like a win-win to
> > > me.

> > > Thanks


> > So, Dmitry, do you mind fixing this in the name of unblocking kernel  
> > testing?


> Let's tell syzbot about the pending fix:

> #syz fix: Input: do not use WARN() in input_alloc_absinfo()

Can't find the corresponding bug.


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