Re: [PATCH 06/13] sysfs: Fix locking and factor out sysfs_sd_setattr

Eric W. Biederman
2009-11-04T12:57:00Z

ebiederm@xmission.com (Eric W. Biederman) writes:

> "Serge E. Hallyn" <serue@us.ibm.com> writes:
>
>> Quoting Eric W. Biederman (ebiederm@xmission.com):
>>> From: Eric W. Biederman <ebiederm@xmission.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@kernel.org>
>>> Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.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. !#@#!#

Turns out it wasn't as bad as it looks because inode_change_ok already
does what I am trying to do properly.

Although come to think of it, SGID on a sysfs file is completely bogus.
We don't exec files and we don't allow users to create anything.

I have already sent the follow up patch to remove those few lines of code.

Eric