UBIFS: fix free log space calculation

commit ba29e721eb2df6df8f33c1f248388bb037a47914 upstream.

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.

Tested-by: hujianyang <hujianyang@huawei.com>
Reported-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ubifs/log.c b/fs/ubifs/log.c
index be67120fb9199a46ff5fec2492e2172de9a87d1d..06649d21b056408398623351d7535a1043a9cf9f 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;
 }
 
 /**