On 4/15/19 11:22 PM, Thomas Gleixner wrote: > On Mon, 15 Apr 2019, Andy Lutomirski wrote: >> On Mon, Apr 15, 2019 at 9:17 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: >>> On Mon, Apr 15, 2019 at 06:07:44PM +0200, Thomas Gleixner wrote: >>>>> Looks like stack_trace.nr_entries isn't initialized? (though this code >>>>> gets eventually replaced by a later patch) >>>> >>>> struct initializer initialized the non mentioned fields to 0, if I'm not >>>> totally mistaken. >>> >>> Hm, it seems you are correct. And I thought I knew C. >>> >>>>> Who actually reads this stack trace? I couldn't find a consumer. >>>> >>>> It's stored directly in the memory pointed to by @addr and that's the freed >>>> cache memory. If that is used later (UAF) then the stack trace can be >>>> printed to see where it was freed. >>> >>> Right... but who reads it? >> >> That seems like a reasonable question. After some grepping and some >> git searching, it looks like there might not be any users. I found > > Anymore. There was something 10y+ ago. In theory it can be useful in a crash dump. But I don't see any related debugging check that would trigger a panic, in order to get one. >> SLAB_STORE_USER, but that seems to be independent. >> >> So maybe the whole mess should just be deleted. If anyone ever >> notices, they can re-add it better. > > No objections from my side, but the mm people might have opinions. Anyone who wants to debug wrong slab usage probably uses SLUB anyway, so I don't think it's a problem to remove broken SLAB debugging. Perhaps even SLAB itself will be removed soon if there's performance data supporting it [1]. [1] https://lore.kernel.org/linux-mm/20190412112816.GD18914@xxxxxxxxxxxxxxxxxxx/T/#u > Thanks, > > tglx >
