From aea4df4c53f754cc229edde6c5465e481311cc49 Mon Sep 17 00:00:00 2001 From: Laura Abbott Date: Fri, 15 Nov 2019 17:34:50 -0800 Subject: [PATCH] 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 Oops: 0000 [#1] PREEMPT SMP PTI RIP: 0010:print_trailer+0x70/0x1d5 Call Trace: free_debug_processing.cold.37+0xc9/0x149 __slab_free+0x22a/0x3d0 kmem_cache_free_bulk+0x415/0x420 __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 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 Reported-by: Thibaut Sautereau Acked-by: David Rientjes Tested-by: Alexander Potapenko Acked-by: Alexander Potapenko Cc: Kees Cook Cc: "David S. Miller" Cc: Vlastimil Babka Cc: Cc: Christoph Lameter Cc: Pekka Enberg Cc: Joonsoo Kim Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 39 +++++++++------------------------------ 1 file changed, 9 insertions(+), 30 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index b25c807a111f..e72e802fc569 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1433,12 +1433,15 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s, 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_hook(struct kmem_cache *s, : 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_hook(struct kmem_cache *s, *tail = NULL; return *head != NULL; -#else - return true; -#endif } static void *setup_object(struct kmem_cache *s, struct page *page,