jffs2: fix NULL pointer dereference in jffs2_scan_medium

hulk inclusion
category: bugfix
bugzilla: 185988, https://gitee.com/openeuler/kernel/issues/I4YVV3

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

In jffs2_scan_medium,
if `s = kzalloc(sizeof(struct jffs2_summary), GFP_KERNEL);` returns error,
go to "out" to do clear. Null pointer dereference occurs when
`if (s->sum_list_head)` is executed in "out".

Fixes: bf7ba557361f ("[Huawei] jffs2: fix memory leak in jffs2_scan_medium")
Signed-off-by: NBaokun Li <libaokun1@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/jffs2/scan.c

@@ -136,7 +136,7 @@ int jffs2_scan_medium(struct jffs2_sb_info *c)
 		if (!s) {
 			JFFS2_WARNING("Can't allocate memory for summary\n");
 			ret = -ENOMEM;
-			goto out;
+			goto out_buf;
 		}
 	}
 
@@ -275,15 +275,15 @@ int jffs2_scan_medium(struct jffs2_sb_info *c)
 	}
 	ret = 0;
  out:
+	jffs2_sum_reset_collected(s);
+	kfree(s);
+ out_buf:
 	if (buf_size)
 		kfree(flashbuf);
 #ifndef __ECOS
 	else
 		mtd_unpoint(c->mtd, 0, c->mtd->size);
 #endif
-	if (s->sum_list_head)
-		jffs2_sum_reset_collected(s);
-	kfree(s);
 	return ret;
 }