On Thu, Jun 20, 2019 at 03:28:01PM -0400, Qian Cai wrote: > The linux-next commit "mm: security: introduce init_on_alloc=1 and > init_on_free=1 boot options" [1] does not play well with SLAB_RED_ZONE > as it will overwrite the right-side redzone with all zeros and triggers > endless errors below. Fix it by only wiping out the slab object size and > leave the redzone along. This has a side-effect that it does not wipe > out the slab object metadata like the free pointer and the tracking data > for SLAB_STORE_USER which does seem important anyway, so just to keep > the code simple. > > [1] https://patchwork.kernel.org/patch/10999465/ > > BUG kmalloc-64 (Tainted: G B ): Redzone overwritten > > INFO: 0x(____ptrval____)-0x(____ptrval____). First byte 0x0 instead of > 0xcc > INFO: Slab 0x(____ptrval____) objects=163 used=4 fp=0x(____ptrval____) > flags=0x3fffc000000201 > INFO: Object 0x(____ptrval____) @offset=58008 fp=0x(____ptrval____) > > Redzone (____ptrval____): cc cc cc cc cc cc cc cc > ........ > Object (____ptrval____): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > ................ > Object (____ptrval____): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > ................ > Object (____ptrval____): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > ................ > Object (____ptrval____): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > ................ > Redzone (____ptrval____): 00 00 00 00 00 00 00 00 > ........ > Padding (____ptrval____): 00 00 00 00 00 00 00 00 > ........ > CPU: 0 PID: 1 Comm: swapper/0 Tainted: G B > 5.2.0-rc5-next-20190620+ #2 > Call Trace: > [c00000002b72f4b0] [c00000000089ce5c] dump_stack+0xb0/0xf4 (unreliable) > [c00000002b72f4f0] [c0000000003e13d8] print_trailer+0x23c/0x264 > [c00000002b72f580] [c0000000003d0468] check_bytes_and_report+0x138/0x160 > [c00000002b72f620] [c0000000003d33dc] check_object+0x2ac/0x3e0 > [c00000002b72f690] [c0000000003da15c] free_debug_processing+0x1ec/0x680 > [c00000002b72f780] [c0000000003da944] __slab_free+0x354/0x6d0 > [c00000002b72f840] [c00000000015600c] > __kthread_create_on_node+0x15c/0x260 > [c00000002b72f910] [c000000000156144] kthread_create_on_node+0x34/0x50 > [c00000002b72f930] [c000000000146fd0] create_worker+0xf0/0x230 > [c00000002b72f9e0] [c00000000014fc6c] workqueue_prepare_cpu+0xdc/0x280 > [c00000002b72fa60] [c00000000011b27c] cpuhp_invoke_callback+0x1bc/0x1220 > [c00000002b72fb00] [c00000000011e7d8] _cpu_up+0x168/0x340 > [c00000002b72fb80] [c00000000011eafc] do_cpu_up+0x14c/0x210 > [c00000002b72fc10] [c000000000aedc90] smp_init+0x17c/0x1f0 > [c00000002b72fcb0] [c000000000ac4a4c] kernel_init_freeable+0x358/0x7cc > [c00000002b72fdb0] [c0000000000106ec] kernel_init+0x2c/0x150 > [c00000002b72fe20] [c00000000000b4cc] ret_from_kernel_thread+0x5c/0x70 > FIX kmalloc-64: Restoring 0x(____ptrval____)-0x(____ptrval____)=0xcc > > FIX kmalloc-64: Object at 0x(____ptrval____) not freed > > Signed-off-by: Qian Cai <cai@xxxxxx> > --- > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index a384228ff6d3..787971d4fa36 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1437,7 +1437,7 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s, > do { > object = next; > next = get_freepointer(s, object); > - memset(object, 0, s->size); > + memset(object, 0, s->object_size); I think this should be more dynamic -- we _do_ want to wipe all of object_size in the case where it's just alignment and padding adjustments. If redzones are enabled, let's remove that portion only. -Kees > set_freepointer(s, object, next); > } while (object != old_tail); > > -- > 1.8.3.1 > -- Kees Cook
