Jeff Layton wrote:
quoted text
> Make notify_change not clear the ATTR_KILL_S*ID bits in the ia_vaid that
> gets passed to the setattr inode operation. This allows the filesystems
> to reinterpret whether this mode change is simply intended to clear the
> setuid/setgid bits.
>
> This means that notify_change should never be called with both ATTR_MODE
> and either of the ATTR_KILL_S*ID bits set, since the filesystem would
> have no way to know what part of the mode change was intentional. If
> it is called this way, consider it a BUG().
>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/attr.c |   22 ++++++++++++----------
>  1 files changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/fs/attr.c b/fs/attr.c
> index ae58bd3..f98d10c 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -103,12 +103,11 @@ EXPORT_SYMBOL(inode_setattr);
>  int notify_change(struct dentry * dentry, struct iattr * attr)
>  {
>  	struct inode *inode = dentry->d_inode;
> -	mode_t mode;
> +	mode_t mode = inode->i_mode;
>  	int error;
>  	struct timespec now;
>  	unsigned int ia_valid = attr->ia_valid;
>  
> -	mode = inode->i_mode;
>  	now = current_fs_time(inode->i_sb);
>  
>  	attr->ia_ctime = now;
> @@ -125,18 +124,21 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
>  		if (error)
>  			return error;
>  	}
> +
> +	/*
> +	 * It's not valid to pass an iattr with both ATTR_MODE and
> +	 * ATTR_KILL_S*ID set.
> +	 */
> +	if (ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID) && ia_valid & ATTR_MODE)
>   

If you would, please add some parentheses to show and make
explicit what the bindings are.  This is:

       if ((ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID)) &&
           (ia_valid & ATTR_MODE))

Thanx...

       ps

quoted text
> +		BUG();
> +
>  	if (ia_valid & ATTR_KILL_SUID) {
> -		attr->ia_valid &= ~ATTR_KILL_SUID;
>  		if (mode & S_ISUID) {
> -			if (!(ia_valid & ATTR_MODE)) {
> -				ia_valid = attr->ia_valid |= ATTR_MODE;
> -				attr->ia_mode = inode->i_mode;
> -			}
> -			attr->ia_mode &= ~S_ISUID;
> +			ia_valid = attr->ia_valid |= ATTR_MODE;
> +			attr->ia_mode = (inode->i_mode & ~S_ISUID);
>  		}
>  	}
>  	if (ia_valid & ATTR_KILL_SGID) {
> -		attr->ia_valid &= ~ ATTR_KILL_SGID;
>  		if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
>  			if (!(ia_valid & ATTR_MODE)) {
>  				ia_valid = attr->ia_valid |= ATTR_MODE;
> @@ -145,7 +147,7 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
>  			attr->ia_mode &= ~S_ISGID;
>  		}
>  	}
> -	if (!attr->ia_valid)
> +	if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
>  		return 0;
>  
>  	if (ia_valid & ATTR_SIZE)
>   

-
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