Messages in this thread | | | Date | Sat, 30 May 2009 15:52:37 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 2/2] tracing/filters: use strcmp() instead of strncmp() |
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On Sat, May 30, 2009 at 05:06:39PM +0800, Li Zefan wrote: > Frédéric Weisbecker wrote: > > 2009/5/29 Li Zefan <lizf@cn.fujitsu.com>: > >> Trace filter is not working normally: > >> > >> # echo 'name == et' > tracing/events/irq/irq_handler_entry/filter > >> # echo 1 > tracing/events/irq/irq_handler_entry/enable > >> # cat trace_pipe > >> <idle>-0 [001] 1363.423175: irq_handler_entry: irq=18 handler=eth0 > >> <idle>-0 [001] 1363.934528: irq_handler_entry: irq=18 handler=eth0 > >> ... > >> > >> It's because we pass to trace_define_field() the information of > >> __str_loc_##item, but not the actual string, so pred->str_len == field->size > >> == sizeof(unsigned short), thus it always compare at most 2 bytes when > >> filtering on __string() field. > > > > > > Weird, I was about sure I set the size of each string() to FILTER_MAX_STRING (or > > something like that). > > > > Anyway this patch looks good but it does more than just fixing the > > issue, it removes > > the string len boundary security we had with strncmp() for every > > string (static and > > dynamic size). > > > > The potential side effect that comes along this patch would disappear if > > you just turn strncmp into strcmp only in filter_pred_strloc(). > > > > If you do that also for fixed size strings, then it should be done in > > a second patch, > > although I guess turning anything here into strcmp is fine because the > > strings given > > by the user are always limited in their size. But we never know... > > > > I don't think there's any security issue. It's irrelevant how big the user-input > strings are. The point is those strings are guaranteed to be NULL-terminated. > Am I missing something? > > And I don't think it's necessary to make 2 patches that each patch converts > one strncmp to strcmp. But maybe it's better to improve this changelog?
Hmm, you must be right, indeed they seem to be guaranted beeing NULL-terminated strings.
But at least improve your changelog to explain why your solution is safe.
Thanks, Frederic.
> > > > Thanks, > > Frederic. > > > > > >> Since __string() is dynamic size, we are not able to set field->size to > >> string length. Thus this patch uses strcmp() instead of strncmp(). > >> > >> [ Impact: make filter facility working normally for __string() field ] > >> > >> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> > >> ---
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