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() -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
