samba/cifs-utils: mount.cifs and umount.cifs fail to anticipate RLIMIT_FSIZE

smbfs in Samba 3.5.8 and earlier attempts to use 1 mount.cifs to append to the /etc/mtab file and 2 umount.cifs to append to the /etc/mtab.tmp file without first checking whether resource limits would interfere, which allows local users to trigger corruption of the /etc/mtab file via a process wi...