Messages in this thread | | | Subject | Re: [syzbot] WARNING: kmalloc bug in xdp_umem_create (2) | From | Daniel Borkmann <> | Date | Tue, 7 Dec 2021 10:19:53 +0100 |
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[ +Andrew ]
On 12/7/21 9:49 AM, Björn Töpel wrote: > On Mon, 6 Dec 2021 at 11:55, syzbot > <syzbot+11421fbbff99b989670e@syzkaller.appspotmail.com> wrote: >> >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: a51e3ac43ddb Merge tag 'net-5.16-rc4' of git://git.kernel... >> git tree: net >> console output: https://syzkaller.appspot.com/x/log.txt?x=17f04ebeb00000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=5b0eee8ab3ea1839 >> dashboard link: https://syzkaller.appspot.com/bug?extid=11421fbbff99b989670e >> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 >> >> Unfortunately, I don't have any reproducer for this issue yet. >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+11421fbbff99b989670e@syzkaller.appspotmail.com >> > > This warning stems from mm/utils.c: > /* Don't even allow crazy sizes */ > if (WARN_ON_ONCE(size > INT_MAX)) > return NULL; > > The structure that is being allocated is the page-pinning accounting. > AF_XDP has an internal limit of U32_MAX pages, which is *a lot*, but > still fewer than what memcg allows (PAGE_COUNTER_MAX is a > LONG_MAX/PAGE_SIZE on 64b systems). > > The (imo hacky) workaround to silence the warning is to decrease the > U32_MAX limit to something that is less than "sizeof householding > struct". > > Note that this is a warning, and not an oops/bug. > > Thoughts?
This is coming from 7661809d493b ("mm: don't allow oversized kvmalloc() calls"). There was a recent discussion on this topic here [0]; this adds another instance.
Iff removal would not be an option, could we maybe add a __GFP_LARGE flag to tag these instances that it is indeed intended that large allocs are allowed (and they would thus bypass this warning)?
Thanks, Daniel
[0] https://lore.kernel.org/bpf/20211201202905.b9892171e3f5b9a60f9da251@linux-foundation.org/
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