[PATCH] btrfs: fix dereference on inode->i_sb before inode null check

[PATCH] btrfs: fix dereference on inode->i_sb before inode null check

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

inode is being deferenced and then inode is checked to see if it
is null, implying we potentially could have a null pointer deference
on inode.

Found with static analysis by CoverityScan, CID 1389472

Fix this by dereferencing inode only after the inode null check.

Fixes: 0b246afa62b0cf5 ("btrfs: root->fs_info cleanup, add fs_info convenience variables")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 fs/btrfs/export.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index 340d907..b746d2b 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -223,7 +223,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
 {
 	struct inode *inode = d_inode(child);
 	struct inode *dir = d_inode(parent);
-	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct btrfs_fs_info *fs_info;
 	struct btrfs_path *path;
 	struct btrfs_root *root = BTRFS_I(dir)->root;
 	struct btrfs_inode_ref *iref;
@@ -241,6 +241,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
 	if (!S_ISDIR(dir->i_mode))
 		return -EINVAL;
 
+	fs_info = btrfs_sb(inode->i_sb);
 	ino = btrfs_ino(inode);
 
 	path = btrfs_alloc_path();
-- 
2.10.2

Re: [PATCH] btrfs: fix dereference on inode->i_sb before inode null check

[Jeff Mahoney]

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On 12/16/16 7:20 AM, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> inode is being deferenced and then inode is checked to see if it
> is null, implying we potentially could have a null pointer deference
> on inode.
> 
> Found with static analysis by CoverityScan, CID 1389472
> 
> Fix this by dereferencing inode only after the inode null check.
> 
> Fixes: 0b246afa62b0cf5 ("btrfs: root->fs_info cleanup, add fs_info convenience variables")

Hi Colin -

Thanks for the review.  The right fix here is to eliminate the tests for
inode == NULL entirely.  This is a callback for exportfs, which will
itself crash if dentry->d_inode or parent->d_inode is NULL.  Removing
the tests would be consistent with other file systems.

-Jeff

> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  fs/btrfs/export.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
> index 340d907..b746d2b 100644
> --- a/fs/btrfs/export.c
> +++ b/fs/btrfs/export.c
> @@ -223,7 +223,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
>  {
>  	struct inode *inode = d_inode(child);
>  	struct inode *dir = d_inode(parent);
> -	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> +	struct btrfs_fs_info *fs_info;
>  	struct btrfs_path *path;
>  	struct btrfs_root *root = BTRFS_I(dir)->root;
>  	struct btrfs_inode_ref *iref;
> @@ -241,6 +241,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
>  	if (!S_ISDIR(dir->i_mode))
>  		return -EINVAL;
>  
> +	fs_info = btrfs_sb(inode->i_sb);
>  	ino = btrfs_ino(inode);
>  
>  	path = btrfs_alloc_path();
> 


-- 
Jeff Mahoney
SUSE Labs


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Re: [PATCH] btrfs: fix dereference on inode->i_sb before inode null check

[Colin Ian King]

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On 16/12/16 15:03, Jeff Mahoney wrote:
> On 12/16/16 7:20 AM, Colin King wrote:
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> inode is being deferenced and then inode is checked to see if it
>> is null, implying we potentially could have a null pointer deference
>> on inode.
>>
>> Found with static analysis by CoverityScan, CID 1389472
>>
>> Fix this by dereferencing inode only after the inode null check.
>>
>> Fixes: 0b246afa62b0cf5 ("btrfs: root->fs_info cleanup, add fs_info convenience variables")
> 
> Hi Colin -
> 
> Thanks for the review.  The right fix here is to eliminate the tests for
> inode == NULL entirely.  This is a callback for exportfs, which will
> itself crash if dentry->d_inode or parent->d_inode is NULL.  Removing
> the tests would be consistent with other file systems.

Ah, thanks for pointing that out. New patch on it's way soon.

Colin

> 
> -Jeff
> 
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>>  fs/btrfs/export.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
>> index 340d907..b746d2b 100644
>> --- a/fs/btrfs/export.c
>> +++ b/fs/btrfs/export.c
>> @@ -223,7 +223,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
>>  {
>>  	struct inode *inode = d_inode(child);
>>  	struct inode *dir = d_inode(parent);
>> -	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>> +	struct btrfs_fs_info *fs_info;
>>  	struct btrfs_path *path;
>>  	struct btrfs_root *root = BTRFS_I(dir)->root;
>>  	struct btrfs_inode_ref *iref;
>> @@ -241,6 +241,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
>>  	if (!S_ISDIR(dir->i_mode))
>>  		return -EINVAL;
>>  
>> +	fs_info = btrfs_sb(inode->i_sb);
>>  	ino = btrfs_ino(inode);
>>  
>>  	path = btrfs_alloc_path();
>>
> 
> 



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