UBIFS: fix free log space calculation

Hu (hujianyang <hujianyang@huawei.com>) discovered an issue in the
'empty_log_bytes()' function, which calculates how many bytes are left in the
log:

"
If 'c->lhead_lnum + 1 == c->ltail_lnum' and 'c->lhead_offs == c->leb_size', 'h'
would equalent to 't' and 'empty_log_bytes()' would return 'c->log_bytes'
instead of 0.
"

At this point it is not clear what would be the consequences of this, and
whether this may lead to any problems, but this patch addresses the issue just
in case.

Cc: stable@vger.kernel.org
Tested-by: hujianyang <hujianyang@huawei.com>
Reported-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

diff --git a/fs/ubifs/log.c b/fs/ubifs/log.c
index 9bd4aafd5c6f21e56683ba3c45eb48681494418d..c14628fbeee2de173015bfd49668175c262287ae 100644 (file)
--- a/fs/ubifs/log.c
+++ b/fs/ubifs/log.c
@@ -106,10 +106,14 @@ static inline long long empty_log_bytes(const struct ubifs_info *c)
        h = (long long)c->lhead_lnum * c->leb_size + c->lhead_offs;
        t = (long long)c->ltail_lnum * c->leb_size;
 
-       if (h >= t)
+       if (h > t)
                return c->log_bytes - h + t;
-       else
+       else if (h != t)
                return t - h;
+       else if (c->lhead_lnum != c->ltail_lnum)
+               return 0;
+       else
+               return c->log_bytes;
 }
 
 /**