f2fs: fix to avoid out-of-boundary access in devs.path

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to avoid out-of-boundary access in devs.path

- touch /mnt/f2fs/012345678901234567890123456789012345678901234567890123

- truncate -s $((1024*1024*1024)) \

/mnt/f2fs/012345678901234567890123456789012345678901234567890123

- touch /mnt/f2fs/file

- truncate -s $((1024*1024*1024)) /mnt/f2fs/file

- mkfs.f2fs /mnt/f2fs/012345678901234567890123456789012345678901234567890123 \

-c /mnt/f2fs/file

- mount /mnt/f2fs/012345678901234567890123456789012345678901234567890123 \

/mnt/f2fs/loop

[16937.192225] F2FS-fs (loop0): Mount Device [ 0]: /mnt/f2fs/012345678901234567890123456789012345678901234567890123\xff\x01, 511, 0 - 3ffff

[16937.192268] F2FS-fs (loop0): Failed to find devices

If device path length equals to MAX_PATH_LEN, sbi->devs.path[] may

not end up w/ null character due to path array is fully filled, So

accidently, fields locate after path[] may be treated as part of

device path, result in parsing wrong device path.

struct f2fs_dev_info {

...

char path[MAX_PATH_LEN];

...

};

Let's add one byte space for sbi->devs.path[] to store null

character of device path string.