fs/f2fs/segment.c in the Linux kernel before 4.13 allows local users to
cause a denial of service (NULL pointer dereference and panic) by using a
noflush_merge option that triggers a NULL value for a flush_cmd_control
data structure.

It was discovered that the f2fs filesystem implementation in the Linux
kernel did not handle the noflush_merge mount option correctly. An attacker
could use this to cause a denial of service (system crash).

 ppisati> fixes a case in the F2FS_FS, when the fs is mounted with the
 ppisati> 'noflush_merge' option, but support for flush coalition was introduced in:
 ppisati> 6b4afdd794783fe515b50838aa36591e3feea990
 tyhicks> The affected user base for this issue is likely small since f2fs is
  not the default filesystem and it is not widely used in Ubuntu