Re: [External] : Re: [PATCH] sched/isolation: avoid reading past string in isolcpus parser

[Joseph Salisbury]

On 3/9/26 10:05 AM, Steven Rostedt wrote:
> On Fri,  6 Mar 2026 14:59:08 -0800
> Joseph Salisbury <joseph.salisbury@xxxxxxxxxx> wrote:
>
> > The function housekeeping_isolcpus_setup() advanced the parser pointer
> > unconditionally after unknown flags.
> >
> > For an argument like 'isolcpus=unknownflag', with no trailing comma, this can
> > move the pointer past the terminating NUL, and the next loop test reads
> > out of bounds.
> >
> > Advance only when the current character is a comma separator, preserving
> > existing parsing semantics while avoiding the invalid read.
> Nice catch.
>
> > Fixes: 3662daf02350 ("sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Assisted-by: Codex:GPT-5.3
> > Signed-off-by: Joseph Salisbury <joseph.salisbury@xxxxxxxxxx>
> > ---
> >   kernel/sched/isolation.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> > index ef152d401fe2..4cf253fb6d75 100644
> > --- a/kernel/sched/isolation.c
> > +++ b/kernel/sched/isolation.c
> > @@ -355,7 +355,8 @@ static int __init housekeeping_isolcpus_setup(char *str)
> >   		}
> >   
> >   		pr_info("isolcpus: Skipped unknown flag %.*s\n", len, par);
> > -		str++;
> > +		if (*str == ',')
> > +			str++;
> Although it should only be a ',' here, I think it's more robust to just
> test against non-nul character. As the bug only triggers if str points to
> the nul character. No need to make this check depend on the rest of the
> algorithm.
>
> 		if (*str)
> 			str++;
>
> -- Steve
Thanks for the feedback and suggestion, Steve!  I'll send a v2 with a 
test for a non-nul character.
> >   	}
> >   
> >   	/* Default behaviour for isolcpus without flags */