From: Laura Abbott labbott@redhat.com Subject: mm: slub: really fix slab walking for init_on_free
Commit 1b7e816fc80e ("mm: slub: Fix slab walking for init_on_free") fixed one problem with the slab walking but missed a key detail: When walking the list, the head and tail pointers need to be updated since we end up reversing the list as a result. Without doing this, bulk free is broken. One way this is exposed is a NULL pointer with slub_debug=F:
============================================================================= BUG skbuff_head_cache (Tainted: G T): Object already free -----------------------------------------------------------------------------
INFO: Slab 0x000000000d2d2f8f objects=16 used=3 fp=0x0000000064309071 flags=0x3fff00000000201 BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 0 PID: 0 Comm: swapper/0 Tainted: G B T 5.3.8 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:print_trailer+0x70/0x1d5 Code: 28 4d 8b 4d 00 4d 8b 45 20 81 e2 ff 7f 00 00 e8 86 ce ef ff 8b 4b 20 48 89 ea 48 89 ee 4c 29 e2 48 c7 c7 90 6f d4 89 48 01 e9 <48> 33 09 48 33 8b 70 01 00 00 e8 61 ce ef ff f6 43 09 04 74 35 8b RSP: 0018:ffffbf7680003d58 EFLAGS: 00010046 RAX: 000000000000005d RBX: ffffa3d2bb08e540 RCX: 0000000000000000 RDX: 00005c2d8fdc2000 RSI: 0000000000000000 RDI: ffffffff89d46f90 RBP: 0000000000000000 R08: 0000000000000242 R09: 000000000000006c R10: 0000000000000000 R11: 0000000000000030 R12: ffffa3d27023e000 R13: fffff11080c08f80 R14: ffffa3d2bb047a80 R15: 0000000000000002 FS: 0000000000000000(0000) GS:ffffa3d2be400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000007a6c4000 CR4: 00000000000006f0 Call Trace: <IRQ> free_debug_processing.cold.37+0xc9/0x149 ? __kfree_skb_flush+0x30/0x40 ? __kfree_skb_flush+0x30/0x40 __slab_free+0x22a/0x3d0 ? tcp_wfree+0x2a/0x140 ? __sock_wfree+0x1b/0x30 kmem_cache_free_bulk+0x415/0x420 ? __kfree_skb_flush+0x30/0x40 __kfree_skb_flush+0x30/0x40 net_rx_action+0x2dd/0x480 __do_softirq+0xf0/0x246 irq_exit+0x93/0xb0 do_IRQ+0xa0/0x110 common_interrupt+0xf/0xf </IRQ>
Given we're now almost identical to the existing debugging code which correctly walks the list, combine with that.
Link: https://lkml.kernel.org/r/20191104170303.GA50361@gandi.net Link: http://lkml.kernel.org/r/20191106222208.26815-1-labbott@redhat.com Fixes: 1b7e816fc80e ("mm: slub: Fix slab walking for init_on_free") Signed-off-by: Laura Abbott labbott@redhat.com Reported-by: Thibaut Sautereau thibaut.sautereau@clip-os.org Acked-by: David Rientjes rientjes@google.com Tested-by: Alexander Potapenko glider@google.com Acked-by: Alexander Potapenko glider@google.com Cc: Kees Cook keescook@chromium.org Cc: "David S. Miller" davem@davemloft.net Cc: Vlastimil Babka vbabka@suse.cz Cc: clipos@ssi.gouv.fr Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/slub.c | 39 +++++++++------------------------------ 1 file changed, 9 insertions(+), 30 deletions(-)
--- a/mm/slub.c~mm-slub-really-fix-slab-walking-for-init_on_free +++ a/mm/slub.c @@ -1433,12 +1433,15 @@ static inline bool slab_free_freelist_ho void *old_tail = *tail ? *tail : *head; int rsize;
- if (slab_want_init_on_free(s)) { - void *p = NULL; + /* Head and tail of the reconstructed freelist */ + *head = NULL; + *tail = NULL; + + do { + object = next; + next = get_freepointer(s, object);
- do { - object = next; - next = get_freepointer(s, object); + if (slab_want_init_on_free(s)) { /* * Clear the object and the metadata, but don't touch * the redzone. @@ -1448,29 +1451,8 @@ static inline bool slab_free_freelist_ho : 0; memset((char *)object + s->inuse, 0, s->size - s->inuse - rsize); - set_freepointer(s, object, p); - p = object; - } while (object != old_tail); - } - -/* - * Compiler cannot detect this function can be removed if slab_free_hook() - * evaluates to nothing. Thus, catch all relevant config debug options here. - */ -#if defined(CONFIG_LOCKDEP) || \ - defined(CONFIG_DEBUG_KMEMLEAK) || \ - defined(CONFIG_DEBUG_OBJECTS_FREE) || \ - defined(CONFIG_KASAN) - - next = *head;
- /* Head and tail of the reconstructed freelist */ - *head = NULL; - *tail = NULL; - - do { - object = next; - next = get_freepointer(s, object); + } /* If object's reuse doesn't have to be delayed */ if (!slab_free_hook(s, object)) { /* Move object to the new freelist */ @@ -1485,9 +1467,6 @@ static inline bool slab_free_freelist_ho *tail = NULL;
return *head != NULL; -#else - return true; -#endif }
static void *setup_object(struct kmem_cache *s, struct page *page, _