On Tue, May 24, 2022 at 3:33 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Sun, May 22, 2022 at 01:26:24PM +0800, Muchun Song wrote:
> > Setting ->proc_handler to proc_dobool at the same time setting ->maxlen
> > to sizeof(int) is counter-intuitive, it is easy to make mistakes. For
> > robustness, fix it by reimplementing proc_dobool() properly.
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Iurii Zaikin <yzaikin@xxxxxxxxxx>
> > ---
> > v2:
> > - Reimplementing proc_dobool().
> >
> > fs/lockd/svc.c | 2 +-
> > kernel/sysctl.c | 38 +++++++++++++++++++-------------------
> > 2 files changed, 20 insertions(+), 20 deletions(-)
> >
> > diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
> > index 59ef8a1f843f..6e48ee787f49 100644
> > --- a/fs/lockd/svc.c
> > +++ b/fs/lockd/svc.c
> > @@ -496,7 +496,7 @@ static struct ctl_table nlm_sysctls[] = {
> > {
> > .procname = "nsm_use_hostnames",
> > .data = &nsm_use_hostnames,
> > - .maxlen = sizeof(int),
> > + .maxlen = sizeof(nsm_use_hostnames),
> > .mode = 0644,
> > .proc_handler = proc_dobool,
> > },
>
> This hunk is fine -- it's a reasonable fix-up.
>
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index e52b6e372c60..50a2c29efc94 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -423,21 +423,6 @@ static void proc_put_char(void **buf, size_t *size, char c)
> > }
> > }
> >
> > -static int do_proc_dobool_conv(bool *negp, unsigned long *lvalp,
> > - int *valp,
> > - int write, void *data)
> > -{
> > - if (write) {
> > - *(bool *)valp = *lvalp;
> > - } else {
> > - int val = *(bool *)valp;
> > -
> > - *lvalp = (unsigned long)val;
> > - *negp = false;
> > - }
> > - return 0;
> > -}
> > -
> > static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
> > int *valp,
> > int write, void *data)
> > @@ -708,16 +693,31 @@ int do_proc_douintvec(struct ctl_table *table, int write,
> > * @lenp: the size of the user buffer
> > * @ppos: file position
> > *
> > - * Reads/writes up to table->maxlen/sizeof(unsigned int) integer
> > - * values from/to the user buffer, treated as an ASCII string.
> > + * Reads/writes up to table->maxlen/sizeof(bool) bool values from/to
> > + * the user buffer, treated as an ASCII string.
> > *
> > * Returns 0 on success.
> > */
> > int proc_dobool(struct ctl_table *table, int write, void *buffer,
> > size_t *lenp, loff_t *ppos)
> > {
> > - return do_proc_dointvec(table, write, buffer, lenp, ppos,
> > - do_proc_dobool_conv, NULL);
> > + struct ctl_table tmp = *table;
> > + bool *data = table->data;
> > + unsigned int val = READ_ONCE(*data);
> > + int ret;
> > +
> > + /* Do not support arrays yet. */
> > + if (table->maxlen != sizeof(bool))
> > + return -EINVAL;
> > +
> > + tmp.maxlen = sizeof(val);
> > + tmp.data = &val;
> > + ret = do_proc_douintvec(&tmp, write, buffer, lenp, ppos, NULL, NULL);
> > + if (ret)
> > + return ret;
> > + if (write)
> > + WRITE_ONCE(*data, val ? true : false);
> > + return 0;
> > }
>
> This part I don't understand -- it just inlines do_proc_dobool_conv(),
> and I think detracts from readability.
>
I think do_proc_dobool_conv() is an abuse of do_proc_dointvec()
since do_proc_dointvec() expects a "int" type data instead of a "bool".
As you can see, there is some cast from bool to int or int to bool
in do_proc_dobool_conv(). And do_proc_dobool_conv() supports
arrays, while proc_dobool() does not support. It is a little ugly to
fix this in __do_proc_dointvec() (I have fixed it in v1 [1]).
This version refers to proc_dou8vec_minmax(). For me, I think it
is cleaner than v1, any thoughts?
[1] https://lore.kernel.org/all/20220519125505.92400-1-songmuchun@xxxxxxxxxxxxx/
