[PATCH 3.13 012/105] UBIFS: fix free log space calculation

[Kamal Mostafa]

3.13.11.10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>

commit ba29e721eb2df6df8f33c1f248388bb037a47914 upstream.

Hu (hujianyang <hujianyang at 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 at huawei.com>
Reported-by: hujianyang <hujianyang at huawei.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ubifs/log.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ubifs/log.c b/fs/ubifs/log.c
index 36bd4ef..bcae6d4 100644
--- 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;
 }
 
 /**
-- 
1.9.1