Messages in this thread | | | Date | Fri, 7 Jan 2022 12:18:42 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH 1/3] tracing/filter: degrade addr in filter_pred_string() from double pointer to pointer |
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On Fri, 7 Jan 2022 12:49:49 +0800 Pingfan Liu <kernelfans@gmail.com> wrote:
> Since FILTER_PTR_STRING has the type of "char *", it is meaningless to > convert it to "char **". Hence degrading addr from double pointer to > single. > > Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Ingo Molnar <mingo@redhat.com> > To: linux-kernel@vger.kernel.org > --- > kernel/trace/trace_events_filter.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c > index c9124038b140..264456e1698f 100644 > --- a/kernel/trace/trace_events_filter.c > +++ b/kernel/trace/trace_events_filter.c > @@ -670,11 +670,11 @@ static int filter_pred_string(struct filter_pred *pred, void *event) > /* Filter predicate for char * pointers */ > static int filter_pred_pchar(struct filter_pred *pred, void *event) > { > - char **addr = (char **)(event + pred->offset); > + char *addr = (char *)(event + pred->offset);
This doesn't look right. The address of the pointer should be in the event. "event" is an address to the content of the event in the kernel ring buffer.
event + pred->offset
Is then the address of position of the event.
Let's say we have an event record at 0xffff8000, and the pred->offset is at 0x10. And the pointer to the string (in user space) is at 0x70008000.
0xffff8000: <heade> 0xffff8010: 0x70008000
0x70008000: "user space sting"
event + pred->offset gives us 0xffff8010
If we now have that as char *addr, then addr is 0xffff8010
> int cmp, match; > - int len = strlen(*addr) + 1; /* including tailing '\0' */ > + int len = strlen(addr) + 1; /* including tailing '\0' */
This would give us the addr = 0xffff8010, which is not where the string exists.
How would this work?
-- Steve
> > - cmp = pred->regex.match(*addr, &pred->regex, len); > + cmp = pred->regex.match(addr, &pred->regex, len); > > match = cmp ^ pred->not; >
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