Jianyong Wu wrote on Wed, Jul 01, 2020:
> In the current setattr implementation in 9p, fid is always retrieved
> from dentry no matter file instance exists or not. There may be
> some info related to opened file instance dropped. so it's better
> to retrieve fid from file instance if file instance is passed to setattr.
>
> for example:
> fd=open("tmp", O_RDWR);
> ftruncate(fd, 10);
>
> The file context related with fd will be lost as fid is always
> retrieved from dentry, then the backend can't get the info of
> file context. It is against the original intention of user and
> may lead to bug.
Thanks for the commit message - still feels a bit odd but at least
correct enough for me :)
> Signed-off-by: Jianyong Wu <[email protected]>
> ---
> fs/9p/vfs_inode.c | 6 +++++-
> fs/9p/vfs_inode_dotl.c | 6 +++++-
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
> index c9255d399917..b33574d347fa 100644
> --- a/fs/9p/vfs_inode.c
> +++ b/fs/9p/vfs_inode.c
> @@ -1100,7 +1100,11 @@ static int v9fs_vfs_setattr(struct dentry *dentry,
> struct iattr *iattr)
>
> retval = -EPERM;
> v9ses = v9fs_dentry2v9ses(dentry);
> - fid = v9fs_fid_lookup(dentry);
> + if (iattr->ia_valid & ATTR_FILE) {
> + fid = iattr->ia_file->private_data;
> + WARN_ON(!fid);
That would crash in 9p_client_wstat a few lines below with the current
else ; so I'm not sure WARN_ON is appropriate with this code.
the snippet I had suggested had v9fs_fid_lookup in a different if, not
as a else statement to avoid this crash (and then warning is OK)
> + } else
> + fid = v9fs_fid_lookup(dentry);
--
Dominique
