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SubjectRe: [PATCH 06/13] sysfs: Fix locking and factor out sysfs_sd_setattr
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"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. !#@#!#

Eric


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