Re: [Crash-utility] [PATCH]: double free in trace extension

On Wed, May 9, 2012 at 3:57 PM, Dave Anderson <anderson(a)redhat.com&gt; wrote: > > > ----- Original Message ----- >> >> First, just like some other contributors, I've come across an >> >> issue >> >> triggered by a dump being corrupt. In my case it's this code in >> >> kernel.c:cpu_maps_init(): >> >> >> >>     if (*maskptr & (0x1UL << c)) { >> >>        cpu = (i * BITS_PER_LONG) + c; >> >>        kt->cpu_flags[cpu] |= mapinfo[m].cpu_flag; >> >>     } >> >> >> >> The mask is corrupt, making Crash believe there are more CPU's >> >> than the >> >> four we have allocated space for in kernel.c:kernel_init. How >> >> do you >> >> think this should be handled? >> > >> > Does the "crash --cpus <number> ..." command-line option work >> > around it? >> > >> >> Nope, setting "--cpus 2" I still arrive at the code above with >> >> (gdb) p/x *maskptr >> $3 = 0x540dcebf >> (gdb) >> >> As you can see, it's not really a valid cpu mask. Either that or I'm >> totally deluded as to the capabilities of the hardware CPU-wise =o) > > Right, I understand that cpu_maps_init() will still be called, and that > kt->cpu_flags will be invalid.  But then what happens? > Well, it will fill in flags for imagined cpus up to #30, since that's the highest bit set in the mask, using those cpu numbers to index into a four element large array allocated on the heap, potentially overwriting stuff it shouldn't. For me, I never actually got any symptoms from it - I just came across it through valgrind while investigating the trace extension problem I reported. /Per