Re: lost connection to test machine (3)

[Dmitry Vyukov]

On Wed, Dec 27, 2017 at 7:18 PM, syzbot
<syzbot+4396883fa8c4f64e0175@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello,
>
> syzkaller hit the following crash on
> beacbc68ac3e23821a681adb30b45dc55b17488d
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
>
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: <syzbot+4396883fa8c4f64e0175@xxxxxxxxxxxxxxxxxxxxxxxxx>
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.

+netfilter maintainers

Here is cleaned reproducer:

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <linux/if.h>
#include <linux/netfilter_ipv4/ip_tables.h>

int main()
{
  int fd;

  fd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);
  struct ipt_replace opt = {};
  opt.num_counters = 1;
  opt.size = -1;
  setsockopt(fd, SOL_IP, 0x40, &opt, 0x4);
  return 0;
}


What happens there is that here:

struct xt_table_info *xt_alloc_table_info(unsigned int size)
{
    ...
    if ((SMP_ALIGN(size) >> PAGE_SHIFT) + 2 > totalram_pages)
        return NULL;

size = -1 and SMP_ALIGN(size) = 0, so this still tries to allocate
4GB+delta bytes.

I don't understand why this uses SMP_ALIGN since we add 2 pages on
top, it seems that we could just drop SMP_ALIGN and local SMP_ALIGN
definition altogether.



> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
>
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
> merged
> into any tree, please reply to this email with:
> #syz fix: exact-commit-title
> If you want to test a patch for this bug, please reply with:
> #syz test: git://repo/address.git branch
> and provide the patch inline or as an attachment.
> To mark this as a duplicate of another syzbot report, please reply with:
> #syz dup: exact-subject-of-another-report
> If it's a one-off invalid bug report, please reply with:
> #syz invalid
> Note: if the crash happens again, it will cause creation of a new bug
> report.
> Note: all commands must start from beginning of the line in the email body.
>
> --
> You received this message because you are subscribed to the Google Groups
> "syzkaller-bugs" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxxx
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/syzkaller-bugs/001a1143d40c2b55b10561566d26%40google.com.
> For more options, visit https://groups.google.com/d/optout.