[PATCH] fs: gfs2: Fix a null-pointer dereference in gfs2_alloc_inode()

[PATCH] fs: gfs2: Fix a null-pointer dereference in gfs2_alloc_inode()

[Jia-Ju Bai]

In gfs2_alloc_inode(), when kmem_cache_alloc() on line 1724 returns
NULL, ip is assigned to NULL. In this case, "return &ip->i_inode" will
cause a null-pointer dereference.

To fix this null-pointer dereference, NULL is returned when ip is NULL.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 fs/gfs2/super.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 0acc5834f653..c07c3f4f8451 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1728,8 +1728,9 @@ static struct inode *gfs2_alloc_inode(struct super_block *sb)
 		memset(&ip->i_res, 0, sizeof(ip->i_res));
 		RB_CLEAR_NODE(&ip->i_res.rs_node);
 		ip->i_rahead = 0;
-	}
-	return &ip->i_inode;
+		return &ip->i_inode;
+	} else
+		return NULL;
 }
 
 static void gfs2_free_inode(struct inode *inode)
-- 
2.17.0

Re: [PATCH] fs: gfs2: Fix a null-pointer dereference in gfs2_alloc_inode()

[Christoph Hellwig]

On Wed, Jul 24, 2019 at 04:43:03PM +0800, Jia-Ju Bai wrote:
> index 0acc5834f653..c07c3f4f8451 100644
> --- a/fs/gfs2/super.c
> +++ b/fs/gfs2/super.c
> @@ -1728,8 +1728,9 @@ static struct inode *gfs2_alloc_inode(struct super_block *sb)
>  		memset(&ip->i_res, 0, sizeof(ip->i_res));
>  		RB_CLEAR_NODE(&ip->i_res.rs_node);
>  		ip->i_rahead = 0;
> -	}
> -	return &ip->i_inode;
> +		return &ip->i_inode;
> +	} else
> +		return NULL;
>  }

No need for an else after a return.  You probably just want to
return early for the NULL case.