Re: [PATCH] vfs: Fix possible chmod/truncate race condition.

From: Dmitri Monakhov
Date: Mon Oct 27 2008 - 03:58:33 EST


Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:

> On Wed, 15 Oct 2008 23:35:27 +0400 Dmitri Monakhov <dmonakhov@xxxxxxxxxx> wrote:
>
>>
>> Signed-off-by: Dmitri Monakhov <dmonakhov@xxxxxxxxxx>
>> ---
>> fs/open.c | 3 +--
>> 1 files changed, 1 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/open.c b/fs/open.c
>> index 07da935..3423b94 100644
>> --- a/fs/open.c
>> +++ b/fs/open.c
>> @@ -214,10 +214,9 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
>> newattrs.ia_valid |= ATTR_FILE;
>> }
>>
>> + mutex_lock(&dentry->d_inode->i_mutex);
>> /* Remove suid/sgid on truncate too */
>> newattrs.ia_valid |= should_remove_suid(dentry);
>> -
>> - mutex_lock(&dentry->d_inode->i_mutex);
>> err = notify_change(dentry, &newattrs);
>> mutex_unlock(&dentry->d_inode->i_mutex);
>> return err;
>
> OK, I give up. What race?
i_mode read not protected by i_mutex in should_remove_suid() and we
may have race condition with chown(). Sorry, seems I've been too crazy
about this. The truth is:
1: No one will call truncate() and chown() concurrently.
2: This race is still possible regardless to this fix.
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