GFS2: fix potential NULL pointer dereference

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=e3c4269d139db7471ee560fb30948179e180b3d4
Commit:     e3c4269d139db7471ee560fb30948179e180b3d4
Parent:     527d1511310a89650000081869260394e20c7013
Author:     Michal Nazarewicz <mina86 at mina86.com>
AuthorDate: Tue Nov 12 13:30:05 2013 +0100
Committer:  Steven Whitehouse <swhiteho at redhat.com>
CommitDate: Thu Nov 21 09:55:45 2013 +0000

    GFS2: fix potential NULL pointer dereference
    
    Commit [e66cf1610: GFS2: Use lockref for glocks] replaced call:
        atomic_read(&gi->gl->gl_ref) == 0
    with:
        __lockref_is_dead(&gl->gl_lockref)
    therefore changing how gl is accessed, from gi->gl to plan gl.
    However, gl can be a NULL pointer, and so gi->gl needs to be
    used instead (which is guaranteed not to be NULL because fo
    the while loop checking that condition).
    
    Signed-off-by: Michal Nazarewicz <mina86 at mina86.com>
    Signed-off-by: Steven Whitehouse <swhiteho at redhat.com>
---
 fs/gfs2/glock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index e66a800..c8420f7 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1899,7 +1899,8 @@ static int gfs2_glock_iter_next(struct gfs2_glock_iter *gi)
 			gi->nhash = 0;
 		}
 	/* Skip entries for other sb and dead entries */
-	} while (gi->sdp != gi->gl->gl_sbd || __lockref_is_dead(&gl->gl_lockref));
+	} while (gi->sdp != gi->gl->gl_sbd ||
+		 __lockref_is_dead(&gi->gl->gl_lockref));
 
 	return 0;
 }