[PATCH V3] UBIFS: return -EINVAL if log head is empty

[Artem Bityutskiy]

On Tue, 2015-02-10 at 11:28 +0800, hujianyang wrote:
> CS node is recognized as a sign in UBIFS log replay mechanism.
> Log relaying during mount should find the CS node in log head
> at beginning and then replay the following uncommitted buds.
> 
> Here is a bug in log replay path: If the log head, which is
> indicated by @log_lnum in mst_node, is empty, current UBIFS
> replay nothing and directly mount the partition without any
> warning. This action will put filesystem in an abnormal state,
> e.g. space management in LPT area is incorrect to the real
> space usage in main area.
> 
> We reproduced this bug by fault injection: turn log head leb
> into all 0xFF. UBIFS driver mount the polluted partition
> normally. But errors occur while running fs_stress on this
> mount:
> 
> [89068.055183] UBI error: ubi_io_read: error -74 (ECC error) while reading 59 bytes from PEB 711:33088, read 59 bytes
> [89068.179877] UBIFS error (pid 10517): ubifs_check_node: bad magic 0x101031, expected 0x6101831
> [89068.179882] UBIFS error (pid 10517): ubifs_check_node: bad node at LEB 591:28992
> [89068.179891] Not a node, first 24 bytes:
> [89068.179892] 00000000: 31 10 10 00 37 84 64 04 10 04 00 00 00 00 00 00 20 00 00 00 02 01 00 00                          1...7.d......... .......
> [89068.180282] UBIFS error (pid 10517): ubifs_read_node: expected node type 2
> 
> This patch fix the problem by checking *lnum* to guarantee
> the empty leb is not log head leb and return an error if the
> log head leb is incorrectly empty. After this, we could catch
> *log head empty* error in place.

Pushed to linux-ubifs.git, thank you!

Artem.