Messages in this thread | | | Date | Tue, 16 Oct 2018 17:29:56 +0200 | From | Christian Brauner <> | Subject | Re: [PATCH v1 2/2] sysctl: handle overflow for file-max |
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On Tue, Oct 16, 2018 at 11:25:42AM -0400, Waiman Long wrote: > On 10/16/2018 11:21 AM, Christian Brauner wrote: > > On Tue, Oct 16, 2018 at 11:13:28AM -0400, Waiman Long wrote: > >> 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. > > This is changed in the new code to LONG_MAX. See the full thread for > > context. There's also an additional explantion in the commit message. > > > >>> }, > >>> { > >>> .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. > > Not completely true though. Try > > > > echo 18446744073709551616 > /proc/sys/fs/file-max > > > > on a system you find acceptable loosing. > > So this is an acceptable user-visible change I'd say. But I'm open to > > other suggestions. > > I am not saying this is unacceptable. I just say this is a user-visible > change and so should be documented somehow. BTW, you cap the max value,
Sure, I'll update linux manpages and I can CC stable on the next round.
> but not the min value. So there is inconsistency. I would say you either > do both, or none of them.
The min value is 0. I don't think it needs to be set explicitly. I just kept the max value because it is != ULONG_MAX but LONG_MAX for file-max.
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