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Date: Wed, 6 Nov 2019 17:22:08 -0500
From: Laura Abbott <labbott@...hat.com>
To: Alexander Potapenko <glider@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Laura Abbott <labbott@...hat.com>, netdev@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>,
Kees Cook <keescook@...omium.org>, clipos@....gouv.fr,
Vlastimil Babka <vbabka@...e.cz>,
Thibaut Sautereau <thibaut.sautereau@...p-os.org>
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
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
Reported-by: Thibaut Sautereau <thibaut.sautereau@...p-os.org>
Fixes: 1b7e816fc80e ("mm: slub: Fix slab walking for init_on_free")
Signed-off-by: Laura Abbott <labbott@...hat.com>
---
mm/slub.c | 39 +++++++++------------------------------
1 file changed, 9 insertions(+), 30 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index dac41cf0b94a..d2445dd1c7ed 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1432,12 +1432,15 @@ 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.
@@ -1447,29 +1450,8 @@ 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 */
@@ -1484,9 +1466,6 @@ 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,
--
2.21.0
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