[PATCH v2] NFSD: Don't clear SUID/SGID after root writing data

[Kinglong Mee <kinglongmee@gmail.com>]

SUID/SGID is not cleared after writing data with (root, local ext4),
#touch test; chmod 4777 test; stat test; echo 1234 > test; stat test;
   File: ‘test’
   Size: 0               Blocks: 0          IO Block: 4096   regular 
empty file
Device: 803h/2051d      Inode: 1200137     Links: 1
Access: (4777/-rwsrwxrwx)  Uid: (    0/    root)   Gid: (    0/    root)
Context: unconfined_u:object_r:admin_home_t:s0
Access: 2014-04-18 21:36:31.016029014 +0800
Modify: 2014-04-18 21:36:31.016029014 +0800
Change: 2014-04-18 21:36:31.026030285 +0800
  Birth: -
   File: ‘test’
   Size: 5               Blocks: 8          IO Block: 4096   regular file
Device: 803h/2051d      Inode: 1200137     Links: 1
Access: (4777/-rwsrwxrwx)  Uid: (    0/    root)   Gid: (    0/    root)
Context: unconfined_u:object_r:admin_home_t:s0
Access: 2014-04-18 21:36:31.016029014 +0800
Modify: 2014-04-18 21:36:31.040032065 +0800
Change: 2014-04-18 21:36:31.040032065 +0800
  Birth: -

With no_root_squash, (root, remote ext4), SUID/SGID are cleared,
#touch test; chmod 4777 test; stat test; echo 1234 > test; stat test;
   File: ‘test’
   Size: 0               Blocks: 0          IO Block: 262144 regular 
empty file
Device: 24h/36d Inode: 786439      Links: 1
Access: (4777/-rwsrwxrwx)  Uid: ( 1000/    test)   Gid: ( 1000/    test)
Context: system_u:object_r:nfs_t:s0
Access: 2014-04-18 21:45:32.155805097 +0800
Modify: 2014-04-18 21:45:32.155805097 +0800
Change: 2014-04-18 21:45:32.168806749 +0800
  Birth: -
   File: ‘test’
   Size: 5               Blocks: 8          IO Block: 262144 regular file
Device: 24h/36d Inode: 786439      Links: 1
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/    test)   Gid: ( 1000/    test)
Context: system_u:object_r:nfs_t:s0
Access: 2014-04-18 21:45:32.155805097 +0800
Modify: 2014-04-18 21:45:32.184808783 +0800
Change: 2014-04-18 21:45:32.184808783 +0800
  Birth: -

This patch drops codes that kills SGID/SUID visibly,
because vfs_writev() can kills it if necessary.

With this patch, the above problem will not exist.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
---
  fs/nfsd/vfs.c | 18 ------------------
  1 file changed, 18 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 16f0673..6aaa305 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -857,20 +857,6 @@ nfsd_vfs_read(struct svc_rqst *rqstp, struct svc_fh 
*fhp, struct file *file,
  	return err;
  }

-static void kill_suid(struct dentry *dentry)
-{
-	struct iattr	ia;
-	ia.ia_valid = ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
-
-	mutex_lock(&dentry->d_inode->i_mutex);
-	/*
-	 * Note we call this on write, so notify_change will not
-	 * encounter any conflicting delegations:
-	 */
-	notify_change(dentry, &ia, NULL);
-	mutex_unlock(&dentry->d_inode->i_mutex);
-}
-
  /*
   * Gathered writes: If another process is currently writing to the file,
   * there's a high chance this is another nfsd (triggered by a bulk write
@@ -942,10 +928,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct 
svc_fh *fhp, struct file *file,
  	nfsdstats.io_write += host_err;
  	fsnotify_modify(file);

-	/* clear setuid/setgid flag after write */
-	if (inode->i_mode & (S_ISUID | S_ISGID))
-		kill_suid(dentry);
-
  	if (stable) {
  		if (use_wgather)
  			host_err = wait_for_concurrent_writes(file);
-- 
1.9.0