[PATCH] jfs: fix shift-out-of-bounds in dbJoin

[Manas Ghandat <ghandatmanas@gmail.com>]

Currently while joining the leaf in a buddy system there is shift out
of bound error in calculation of BUDSIZE. Added the required check 
to the BUDSIZE and fixed the documentation as well.

Reported-by: syzbot+411debe54d318eaed386@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=411debe54d318eaed386
Signed-off-by: Manas Ghandat <ghandatmanas@gmail.com>
---
 fs/jfs/jfs_dmap.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 6b838d3ae7c2..baa97bda1c7a 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2730,7 +2730,9 @@ static int dbBackSplit(dmtree_t * tp, int leafno)
  *	leafno	- the number of the leaf to be updated.
  *	newval	- the new value for the leaf.
  *
- * RETURN VALUES: none
+ * RETURN VALUES:
+ *  0		- success
+ *	-EIO	- i/o error
  */
 static int dbJoin(dmtree_t * tp, int leafno, int newval)
 {
@@ -2757,6 +2759,10 @@ static int dbJoin(dmtree_t * tp, int leafno, int newval)
 		 * get the buddy size (number of words covered) of
 		 * the new value.
 		 */
+
+		if ((newval - tp->dmt_budmin) > BUDMIN)
+			return -EIO;
+
 		budsz = BUDSIZE(newval, tp->dmt_budmin);
 
 		/* try to join.
-- 
2.37.2

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