On Thu, Sep 28, 2017 at 04:37:46PM +0200, Daniel Borkmann wrote: > On 09/28/2017 01:27 PM, Mark Rutland wrote: > >Hi, > > > >While fuzzing v4.14-rc2 with Syzkaller, I found it was possible to trigger the > >warning at mm/percpu.c:1361, on both arm64 and x86_64. This appears to require > >increasing RLIMIT_MEMLOCK, so to the best of my knowledge this cannot be > >triggered by an unprivileged user. > > > >I've included example splats for both x86_64 and arm64, along with a C > >reproducer, inline below. > > > >It looks like dev_map_alloc() requests a percpu alloction of 32776 bytes, which > >is larger than the maximum supported allocation size of 32768 bytes. > > > >I wonder if it would make more sense to pr_warn() for sizes that are too > >large, so that callers don't have to roll their own checks against > >PCPU_MIN_UNIT_SIZE? > > Perhaps the pr_warn() should be ratelimited; or could there be an > option where we only return NULL, not triggering a warn at all (which > would likely be what callers might do anyway when checking against > PCPU_MIN_UNIT_SIZE and then bailing out)? Those both make sense to me; checking __GFP_NOWARN should be easy enough. Just to check, do you think that dev_map_alloc() should explicitly test the size against PCPU_MIN_UNIT_SIZE, prior to calling pcpu_alloc()? I can spin both patches if so. Thanks, Mark. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
