linux-kernel - Re: [PATCH 06/13] sysfs: Fix locking and factor out sysfs_sd

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Message-ID: <m1fx8vdk4a.fsf@fess.ebiederm.org>
Date:	Tue, 03 Nov 2009 19:49:57 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>, Greg KH <greg@...ah.com>,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	linux-fsdevel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Benjamin LaHaise <bcrl@...et.ca>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 06/13] sysfs: Fix locking and factor out sysfs_sd_setattr

"Serge E. Hallyn" <serue@...ibm.com> writes:

> Quoting Eric W. Biederman (ebiederm@...ssion.com):
>> From: Eric W. Biederman <ebiederm@...ssion.com>
>> 
>> Cleanly separate the work that is specific to setting the
>> attributes of a sysfs_dirent from what is needed to update
>> the attributes of a vfs inode.
>> 
>> Additionally grab the sysfs_mutex to keep any nasties from
>> surprising us when updating the sysfs_dirent.
>> 
>> Acked-by: Tejun Heo <tj@...nel.org>
>> Signed-off-by: Eric W. Biederman <ebiederm@...stanetworks.com>
>> ---
>>  fs/sysfs/inode.c |   52 ++++++++++++++++++++++++++++++++--------------------
>>  fs/sysfs/sysfs.h |    1 +
>>  2 files changed, 33 insertions(+), 20 deletions(-)
>> 
>> diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
>> index fed7a74..fccfb55 100644
>> --- a/fs/sysfs/inode.c
>> +++ b/fs/sysfs/inode.c
>> @@ -64,30 +64,15 @@ struct sysfs_inode_attrs *sysfs_init_inode_attrs(struct sysfs_dirent *sd)
>> 
>>  	return attrs;
>>  }
>> -int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>> +
>> +int sysfs_sd_setattr(struct sysfs_dirent *sd, struct iattr * iattr)
>>  {
>> -	struct inode * inode = dentry->d_inode;
>> -	struct sysfs_dirent * sd = dentry->d_fsdata;
>>  	struct sysfs_inode_attrs *sd_attrs;
>>  	struct iattr *iattrs;
>>  	unsigned int ia_valid = iattr->ia_valid;
>> -	int error;
>> -
>> -	if (!sd)
>> -		return -EINVAL;
>> 
>>  	sd_attrs = sd->s_iattr;
>> 
>> -	error = inode_change_ok(inode, iattr);
>> -	if (error)
>> -		return error;
>> -
>> -	iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
>> -
>> -	error = inode_setattr(inode, iattr);
>> -	if (error)
>> -		return error;
>> -
>>  	if (!sd_attrs) {
>>  		/* setting attributes for the first time, allocate now */
>>  		sd_attrs = sysfs_init_inode_attrs(sd);
>> @@ -110,12 +95,39 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>>  			iattrs->ia_ctime = iattr->ia_ctime;
>>  		if (ia_valid & ATTR_MODE) {
>>  			umode_t mode = iattr->ia_mode;
>> -
>> -			if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
>> -				mode &= ~S_ISGID;
>>  			iattrs->ia_mode = sd->s_mode = mode;
>>  		}
>>  	}
>> +	return 0;
>> +}
>> +
>> +int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>> +{
>> +	struct inode * inode = dentry->d_inode;
>> +	struct sysfs_dirent * sd = dentry->d_fsdata;
>> +	int error;
>> +
>> +	if (!sd)
>> +		return -EINVAL;
>> +
>> +	error = inode_change_ok(inode, iattr);
>> +	if (error)
>> +		return error;
>> +
>> +	iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
>> +	if (iattr->ia_valid & ATTR_MODE) {
>> +		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
>> +			iattr->ia_mode &= ~S_ISGID;
>> +	}
>
> Was it a bug that before this patch this wasn't cleared before the
> actual inode_setattr()?

Not strictly as inode_setattr performs the exact same check.

> Since the S_ISGID will be set for the *new* gid, that is,
> iattr->ia_gid, shouldn't the user be required to be
> in_group_p(iattr->i_gid)?  Note you haven't done the
> inode_setattr() yet.

Interesting point, yes I am potentially testing the wrong gid
there.  The dangers of moving code around.

Thank you for catching that.  !#@#!#

Eric
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