exfat: fix used_clusters accounting during cluster allocation

In the current exfat_alloc_cluster(), p_chain->size is incremented as
each cluster is allocated so that the partially allocated chain can
be freed by __exfat_free_cluster() on the error path.

However, sbi->used_clusters is still updated only after all clusters
have been allocated, while __exfat_free_cluster() unconditionally
subtracts the number of freed clusters from sbi->used_clusters.
Therefore, when allocation fails partway through, the partially
allocated clusters are subtracted from sbi->used_clusters even
though they were never added to it. This corrupts the free-space
accounting and can cause sbi->used_clusters to underflow.

Increment sbi->used_clusters together with p_chain->size as each
cluster is allocated. This keeps the accounting consistent with
__exfat_free_cluster() on both the success and error paths.

This issue is caught by generic/476 with 256k cluster size:

    Ran: generic/476
    Failures: generic/476
    Failed 1 of 1 tests

    *** fsck.exfat output ***
    ERROR: <path>: more clusters are allocated. truncate to N bytes
    ...
    /dev/vdc: corrupted. directories 331, files 526
    /dev/vdc: files corrupted 9, files fixed 0
    *** end fsck.exfat output ***

Fixes: d5c514b6a0c0 ("exfat: fix the newly allocated clusters are not freed in error handling")
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions