On Wed, Mar 31, 2021 at 11:36:28PM -0500, Eric W. Biederman wrote: > Josh Hunt <joh...@akamai.com> writes: > > > Currently only root can write files under /proc/pressure. Relax this to > > allow tasks running as unprivileged users with CAP_SYS_RESOURCE to be > > able to write to these files. > > The test for CAP_SYS_RESOURCE really needs to be in open rather > than in write. > > Otherwise a suid root executable could have stdout redirected > into these files.
Right. Or check against f_cred. (See uses of kallsyms_show_value()) https://www.kernel.org/doc/html/latest/security/credentials.html#open-file-credentials -Kees > > Eric > > > > Signed-off-by: Josh Hunt <joh...@akamai.com> > > --- > > kernel/sched/psi.c | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > > index b1b00e9bd7ed..98ff7baf1ba8 100644 > > --- a/kernel/sched/psi.c > > +++ b/kernel/sched/psi.c > > @@ -1270,6 +1270,9 @@ static ssize_t psi_write(struct file *file, const > > char __user *user_buf, > > if (!nbytes) > > return -EINVAL; > > > > + if (!capable(CAP_SYS_RESOURCE)) > > + return -EPERM; > > + > > buf_size = min(nbytes, sizeof(buf)); > > if (copy_from_user(buf, user_buf, buf_size)) > > return -EFAULT; > > @@ -1353,9 +1356,9 @@ static int __init psi_proc_init(void) > > { > > if (psi_enable) { > > proc_mkdir("pressure", NULL); > > - proc_create("pressure/io", 0, NULL, &psi_io_proc_ops); > > - proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops); > > - proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops); > > + proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops); > > + proc_create("pressure/memory", 0666, NULL, > > &psi_memory_proc_ops); > > + proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops); > > } > > return 0; > > } -- Kees Cook
