linux-kernel - [PATCH] btrfs: Fix incorrect check causing NULL pointer derefernce

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Date:   Sun, 15 Dec 2019 11:32:26 -0600
From:   Aditya Pakki <pakki001@....edu>
To:     pakki001@....edu
Cc:     kjlu@....edu, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] btrfs: Fix incorrect check causing NULL pointer derefernce

In btrfsic_process_superblock, argument state is dereferenced for
the variable fs_info and then checked for NULL. The patch fixes
this issue by returning an error if state is NULL and then assigns
fs_info.

Signed-off-by: Aditya Pakki <pakki001@....edu>
---
 fs/btrfs/check-integrity.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 0b52ab4cb964..70d7a05cafad 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -629,15 +629,18 @@ static struct btrfsic_dev_state *btrfsic_dev_state_hashtable_lookup(dev_t dev,
 static int btrfsic_process_superblock(struct btrfsic_state *state,
 				      struct btrfs_fs_devices *fs_devices)
 {
-	struct btrfs_fs_info *fs_info = state->fs_info;
-	struct btrfs_super_block *selected_super;
+	struct btrfsic_dev_state *selected_dev_state = NULL;
 	struct list_head *dev_head = &fs_devices->devices;
+	struct btrfs_super_block *selected_super;
+	struct btrfs_fs_info *fs_info;
 	struct btrfs_device *device;
-	struct btrfsic_dev_state *selected_dev_state = NULL;
 	int ret = 0;
 	int pass;
 
-	BUG_ON(NULL == state);
+	if (!state)
+		return -EINVAL;
+
+	fs_info = state->fs_info;
 	selected_super = kzalloc(sizeof(*selected_super), GFP_NOFS);
 	if (NULL == selected_super) {
 		pr_info("btrfsic: error, kmalloc failed!\n");
-- 
2.20.1