On Tue, Sep 12, 2023 at 06:30:46AM +0100, Matthew Wilcox wrote: > On Tue, Sep 05, 2023 at 06:03:49PM -0700, syzbot wrote: > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: a47fc304d2b6 Add linux-next specific files for 20230831 > > git tree: linux-next > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=16502ddba80000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=6ecd2a74f20953b9 > > dashboard link: https://syzkaller.appspot.com/bug?extid=b591856e0f0139f83023 > > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=120e7d70680000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1523f9c0680000 > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/b2e8f4217527/disk-a47fc304.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/ed6cdcc09339/vmlinux-a47fc304.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/bd9b2475bf5a/bzImage-a47fc304.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+b591856e0f0139f83023@xxxxxxxxxxxxxxxxxxxxxxxxx > > #syz test > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 42b5567e3773..90ad5fe60824 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1342,6 +1342,7 @@ static long do_mbind(unsigned long start, unsigned long len, > vma_iter_init(&vmi, mm, start); > prev = vma_prev(&vmi); > for_each_vma_range(vmi, vma, end) { > + vma_start_write(vma); > err = mbind_range(&vmi, vma, &prev, start, end, new); > if (err) > break; Suren, can you take a look at this? The VMA should be locked by the call to queue_pages_range(), but by the time we get to here, the VMA isn't locked. I don't see anywhere that we cycle the mmap_lock (which would unlock the VMA), but I could have missed something. The two VMA walks should walk over the same set of VMAs. Certainly the VMA being dumped should have been locked by the pagewalk: vma ffff888077381a00 start 0000000020c2a000 end 0000000021000000 mm ffff8880258a8980 prot 25 anon_vma 0000000000000000 vm_ops 0000000000000000 pgoff 20c2a file 0000000000000000 private_data 0000000000000000 flags: 0x8100077(read|write|exec|mayread|maywrite|mayexec|account|softdirty) syscall(__NR_mbind, /*addr=*/0x20400000ul, /*len=*/0xc00000ul, /*mode=*/4ul, /*nodemask=*/0ul, /*maxnode=*/0ul, /*flags=*/3ul); 20400000 + c00000 should overlap 20c2a000-21000000
