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Re: [PATCH] xfs: only clear the suid bit once in xfs_write

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: only clear the suid bit once in xfs_write
From: Alex Elder <aelder@xxxxxxx>
Date: Tue, 09 Feb 2010 14:22:53 -0600
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20100203194331.GA20199@xxxxxxxxxxxxx>
References: <20100203194331.GA20199@xxxxxxxxxxxxx>
Reply-to: aelder@xxxxxxx
On Wed, 2010-02-03 at 14:43 -0500, Christoph Hellwig wrote:
> file_remove_suid already calls into ->setattr to clear the suid and sgid
> bits if needed, no need to start a second transaction to do it ourselves.
> 
> Note that xfs_write_clear_setuid issues a sync transaction while the
> path through ->setattr doesn't, but that is consistant with the other
> filesystems.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Looks good.  Those S*ID bits sure get checked and
cleared in a lot of places...

Reviewed-by: Alex Elder <aelder@xxxxxxx>

> Index: xfs/fs/xfs/linux-2.6/xfs_lrw.c
> ===================================================================
> --- xfs.orig/fs/xfs/linux-2.6/xfs_lrw.c       2010-02-03 20:37:45.956003749 
> +0100
> +++ xfs/fs/xfs/linux-2.6/xfs_lrw.c    2010-02-03 20:37:49.348003520 +0100
> @@ -630,18 +630,9 @@ start:
>        * by root.  This keeps people from modifying setuid and
>        * setgid binaries.
>        */
> -
> -     if (((xip->i_d.di_mode & S_ISUID) ||
> -         ((xip->i_d.di_mode & (S_ISGID | S_IXGRP)) ==
> -             (S_ISGID | S_IXGRP))) &&
> -          !capable(CAP_FSETID)) {
> -             error = xfs_write_clear_setuid(xip);
> -             if (likely(!error))
> -                     error = -file_remove_suid(file);
> -             if (unlikely(error)) {
> -                     goto out_unlock_internal;
> -             }
> -     }
> +     error = -file_remove_suid(file);
> +     if (unlikely(error))
> +             goto out_unlock_internal;
>  
>       /* We can write back this queue in page reclaim */
>       current->backing_dev_info = mapping->backing_dev_info;
> Index: xfs/fs/xfs/xfs_rw.c
> ===================================================================
> --- xfs.orig/fs/xfs/xfs_rw.c  2010-02-03 20:37:45.965004126 +0100
> +++ xfs/fs/xfs/xfs_rw.c       2010-02-03 20:37:49.349010212 +0100
> @@ -47,48 +47,6 @@
>  #include "xfs_trace.h"
>  
>  /*
> - * This is a subroutine for xfs_write() and other writers (xfs_ioctl)
> - * which clears the setuid and setgid bits when a file is written.
> - */
> -int
> -xfs_write_clear_setuid(
> -     xfs_inode_t     *ip)
> -{
> -     xfs_mount_t     *mp;
> -     xfs_trans_t     *tp;
> -     int             error;
> -
> -     mp = ip->i_mount;
> -     tp = xfs_trans_alloc(mp, XFS_TRANS_WRITEID);
> -     if ((error = xfs_trans_reserve(tp, 0,
> -                                   XFS_WRITEID_LOG_RES(mp),
> -                                   0, 0, 0))) {
> -             xfs_trans_cancel(tp, 0);
> -             return error;
> -     }
> -     xfs_ilock(ip, XFS_ILOCK_EXCL);
> -     xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
> -     xfs_trans_ihold(tp, ip);
> -     ip->i_d.di_mode &= ~S_ISUID;
> -
> -     /*
> -      * Note that we don't have to worry about mandatory
> -      * file locking being disabled here because we only
> -      * clear the S_ISGID bit if the Group execute bit is
> -      * on, but if it was on then mandatory locking wouldn't
> -      * have been enabled.
> -      */
> -     if (ip->i_d.di_mode & S_IXGRP) {
> -             ip->i_d.di_mode &= ~S_ISGID;
> -     }
> -     xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
> -     xfs_trans_set_sync(tp);
> -     error = xfs_trans_commit(tp, 0);
> -     xfs_iunlock(ip, XFS_ILOCK_EXCL);
> -     return 0;
> -}
> -
> -/*
>   * Force a shutdown of the filesystem instantly while keeping
>   * the filesystem consistent. We don't do an unmount here; just shutdown
>   * the shop, make sure that absolutely nothing persistent happens to
> Index: xfs/fs/xfs/xfs_rw.h
> ===================================================================
> --- xfs.orig/fs/xfs/xfs_rw.h  2010-02-03 20:37:53.085003394 +0100
> +++ xfs/fs/xfs/xfs_rw.h       2010-02-03 20:37:57.946033654 +0100
> @@ -39,7 +39,6 @@ xfs_fsb_to_db(struct xfs_inode *ip, xfs_
>  /*
>   * Prototypes for functions in xfs_rw.c.
>   */
> -extern int xfs_write_clear_setuid(struct xfs_inode *ip);
>  extern int xfs_read_buf(struct xfs_mount *mp, xfs_buftarg_t *btp,
>                       xfs_daddr_t blkno, int len, uint flags,
>                       struct xfs_buf **bpp);
> 
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