Messages in this thread | | | Subject | Re: [PATCH v1 2/2] sysctl: handle overflow for file-max | From | Waiman Long <> | Date | Tue, 16 Oct 2018 11:13:28 -0400 |
| |
On 10/15/2018 06:55 AM, Christian Brauner wrote: > Currently, when writing > > echo 18446744073709551616 > /proc/sys/fs/file-max > > /proc/sys/fs/file-max will overflow and be set to 0. That quickly > crashes the system. > This commit explicitly caps the value for file-max to ULONG_MAX. > > Note, this isn't technically necessary since proc_get_long() will already > return ULONG_MAX. However, two reason why we still should do this: > 1. it makes it explicit what the upper bound of file-max is instead of > making readers of the code infer it from proc_get_long() themselves > 2. other tunebles than file-max may want to set a lower max value than > ULONG_MAX and we need to enable __do_proc_doulongvec_minmax() to handle > such cases too > > Cc: Kees Cook <keescook@chromium.org> > Signed-off-by: Christian Brauner <christian@brauner.io> > --- > v0->v1: > - if max value is < than ULONG_MAX use max as upper bound > - (Dominik) remove double "the" from commit message > --- > kernel/sysctl.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 97551eb42946..226d4eaf4b0e 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -127,6 +127,7 @@ static int __maybe_unused one = 1; > static int __maybe_unused two = 2; > static int __maybe_unused four = 4; > static unsigned long one_ul = 1; > +static unsigned long ulong_max = ULONG_MAX; > static int one_hundred = 100; > static int one_thousand = 1000; > #ifdef CONFIG_PRINTK > @@ -1696,6 +1697,7 @@ static struct ctl_table fs_table[] = { > .maxlen = sizeof(files_stat.max_files), > .mode = 0644, > .proc_handler = proc_doulongvec_minmax, > + .extra2 = &ulong_max,
What is the point of having a maximum value of ULONG_MAX anyway? No value you can put into a ulong type can be bigger than that.
> }, > { > .procname = "nr_open", > @@ -2795,6 +2797,8 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int > break; > if (neg) > continue; > + if (max && val > *max) > + val = *max; > val = convmul * val / convdiv; > if ((min && val < *min) || (max && val > *max)) > continue;
This does introduce a change in behavior. Previously the out-of-bound value is ignored, now it is capped at its maximum. This is a user-visible change.
Cheers, Longman
| |