On 5/28/19 1:54 PM, Johannes Lundberg wrote:
> Author: johalun
> Date: Tue May 28 20:54:59 2019
> New Revision: 348338
> URL: https://svnweb.freebsd.org/changeset/base/348338
>
> Log:
> pseudofs: Ignore unsupported commands in vop_setattr.
>
> Users of pseudofs (e.g. lindebugfs), should be able to receive
> input from command line via commands like "echo 1 > /path/to/file".
> Currently this fails because sh tries to truncate the file first and
> vop_setattr returns not supported error for this. This patch simply
> ignores the error and returns 0 instead.
>
> Reviewed by: imp (mentor), asomers
> Approved by: imp (mentor), asomers
> MFC after: 1 week
> Differential Revision: D20451
FYI, this is supposed to be the URL which makes it easier to click in many
e-mail clients. It seems a recent change in phab that it honors just the
'Dxxxx' tag as previously the URL was required for auto-close. (I sure
wish the phab team would communicate when they change things like this.)
> Modified:
> head/sys/fs/pseudofs/pseudofs_vnops.c
>
> Modified: head/sys/fs/pseudofs/pseudofs_vnops.c
> ==============================================================================
> --- head/sys/fs/pseudofs/pseudofs_vnops.c Tue May 28 20:44:23 2019
> (r348337)
> +++ head/sys/fs/pseudofs/pseudofs_vnops.c Tue May 28 20:54:59 2019
> (r348338)
> @@ -967,7 +967,8 @@ pfs_setattr(struct vop_setattr_args *va)
> PFS_TRACE(("%s", pn->pn_name));
> pfs_assert_not_owned(pn);
>
> - PFS_RETURN (EOPNOTSUPP);
> + /* Silently ignore unchangeable attributes. */
> + PFS_RETURN (0);
Did you consider only whitelisting setattr calls that set the size? This
allows things like chown/chmod that won't actually work which might be
confusing to users.
You can see examples of how to do this in, e.g. ufs_setattr. The interface
for VOP_SETATTR is that the various fields in vattr are set to VNOVAL by
via VATTR_NULL and then the caller sets the fields they want to change. You
can then reject attempts to set attributes you don't support. (e.g. see how
ufs_setattr fails with EINVAL if fields it doesn't support aren't set to
VNOVAL).
You should also likely validate the passed in size and only permit a size of 0
for [f]truncate().
--
John Baldwin
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