[Patch v2] btrfs: use file_remove_suid() after i_mutex is held

[Patch v2] btrfs: use file_remove_suid() after i_mutex is held

[Amerigo Wang]

V1 -> V2:
Move kmalloc() before mutex_lock(), suggested by Arjan.

file_remove_suid() should be called with i_mutex held,
file_update_time() too. So move them after mutex_lock().

Plus, check the return value of kmalloc().

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Arjan <arjan@infradead.org>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Yan Zheng <zheng.yan@oracle.com>
Cc: Sven Wegener <sven.wegener@stealer.net>
Cc: Josef Bacik <jbacik@redhat.com>
Cc: Jeff Mahoney <jeffm@suse.com>

---
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 7c3cd24..09ef5d6 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -944,14 +944,17 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
 	if (count == 0)
 		goto out_nolock;
 
+	pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
+	if (!pages)
+		goto out_nolock;
+
+	mutex_lock(&inode->i_mutex);
+
 	err = file_remove_suid(file);
 	if (err)
-		goto out_nolock;
+		goto out;
 	file_update_time(file);
 
-	pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
-
-	mutex_lock(&inode->i_mutex);
 	BTRFS_I(inode)->sequence++;
 	first_index = pos >> PAGE_CACHE_SHIFT;
 	last_index = (pos + count) >> PAGE_CACHE_SHIFT;

Re: [Patch v2] btrfs: use file_remove_suid() after i_mutex is held

[Tao Ma]

Hi Amerigo,

Amerigo Wang wrote:
> V1 -> V2:
> Move kmalloc() before mutex_lock(), suggested by Arjan.
> 
> file_remove_suid() should be called with i_mutex held,
> file_update_time() too. So move them after mutex_lock().
> 
> Plus, check the return value of kmalloc().
> 
> Signed-off-by: WANG Cong <amwang@redhat.com>
> Cc: Arjan <arjan@infradead.org>
> Cc: Chris Mason <chris.mason@oracle.com>
> Cc: Yan Zheng <zheng.yan@oracle.com>
> Cc: Sven Wegener <sven.wegener@stealer.net>
> Cc: Josef Bacik <jbacik@redhat.com>
> Cc: Jeff Mahoney <jeffm@suse.com>
> 
> ---
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 7c3cd24..09ef5d6 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -944,14 +944,17 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
>  	if (count == 0)
>  		goto out_nolock;
>  
> +	pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
> +	if (!pages)
> +		goto out_nolock;
I guess you need to set err to -ENOMEM here so that the caller knows 
what's wrong. With your patch, this function just return 0(since 
num_written and err are both 0) with no error, and I guess it is worse 
than kernel BUG out when the NULL pages is used later.

Regards,
Tao

Re: [Patch v2] btrfs: use file_remove_suid() after i_mutex is held

[Amerigo Wang]

Tao Ma wrote:
> Hi Amerigo,
>
> Amerigo Wang wrote:
>> V1 -> V2:
>> Move kmalloc() before mutex_lock(), suggested by Arjan.
>>
>> file_remove_suid() should be called with i_mutex held,
>> file_update_time() too. So move them after mutex_lock().
>>
>> Plus, check the return value of kmalloc().
>>
>> Signed-off-by: WANG Cong <amwang@redhat.com>
>> Cc: Arjan <arjan@infradead.org>
>> Cc: Chris Mason <chris.mason@oracle.com>
>> Cc: Yan Zheng <zheng.yan@oracle.com>
>> Cc: Sven Wegener <sven.wegener@stealer.net>
>> Cc: Josef Bacik <jbacik@redhat.com>
>> Cc: Jeff Mahoney <jeffm@suse.com>
>>
>> ---
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index 7c3cd24..09ef5d6 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -944,14 +944,17 @@ static ssize_t btrfs_file_write(struct file 
>> *file, const char __user *buf,
>>      if (count == 0)
>>          goto out_nolock;
>>  
>> +    pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
>> +    if (!pages)
>> +        goto out_nolock;
> I guess you need to set err to -ENOMEM here so that the caller knows 
> what's wrong. With your patch, this function just return 0(since 
> num_written and err are both 0) with no error, and I guess it is worse 
> than kernel BUG out when the NULL pages is used later.

Agree. Thanks, I will update it.