On Tue, Nov 12, 2019 at 3:22 PM Christian Brauner
<christian.brauner@xxxxxxxxxx> wrote:
>
> [Cc+ linux-api@xxxxxxxxxxxxxxx]
>
> since that's potentially relevant to quite a few people.
>
> On Sun, Nov 03, 2019 at 04:55:48PM +0200, Topi Miettinen wrote:
> > Several items in /proc/sys need not be accessible to unprivileged
> > tasks. Let the system administrator change the permissions, but only
> > to more restrictive modes than what the sysctl tables allow.
> >
> > Signed-off-by: Topi Miettinen <toiwoton@xxxxxxxxx>
> > ---
> > fs/proc/proc_sysctl.c | 41 +++++++++++++++++++++++++++++++----------
> > 1 file changed, 31 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > index d80989b6c344..88c4ca7d2782 100644
> > --- a/fs/proc/proc_sysctl.c
> > +++ b/fs/proc/proc_sysctl.c
> > @@ -818,6 +818,10 @@ static int proc_sys_permission(struct inode *inode, int
> > mask)
> > if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
> > return -EACCES;
> >
> > + error = generic_permission(inode, mask);
> > + if (error)
> > + return error;
> > +
> > head = grab_header(inode);
> > if (IS_ERR(head))
> > return PTR_ERR(head);
> > @@ -837,9 +841,35 @@ static int proc_sys_setattr(struct dentry *dentry,
> > struct iattr *attr)
> > struct inode *inode = d_inode(dentry);
> > int error;
> >
> > - if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
> > + if (attr->ia_valid & (ATTR_UID | ATTR_GID))
> > return -EPERM;
Supporting at least ATTR_GID would make this much more useful.
> >
> > + if (attr->ia_valid & ATTR_MODE) {
> > + struct ctl_table_header *head = grab_header(inode);
> > + struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> > + umode_t max_mode = 0777; /* Only these bits may change */
> > +
> > + if (IS_ERR(head))
> > + return PTR_ERR(head);
> > +
> > + if (!table) /* global root - r-xr-xr-x */
> > + max_mode &= ~0222;
> > + else /*
> > + * Don't allow permissions to become less
> > + * restrictive than the sysctl table entry
> > + */
> > + max_mode &= table->mode;
Style nit: please put braces around multi-line if and else branches,
even if they're only multi-line because of comments.
> > +
> > + sysctl_head_finish(head);
> > +
> > + /* Execute bits only allowed for directories */
> > + if (!S_ISDIR(inode->i_mode))
> > + max_mode &= ~0111;
Why is this needed?
