[PATCH 4.19 05/36] mm/slub.c: fix corrupted freechain in deactivate_slab()

Greg Kroah-Hartman
2020-07-07T15:34:26Z

From: Dongli Zhang <dongli.zhang@oracle.com>

[ Upstream commit 52f23478081ae0dcdb95d1650ea1e7d52d586829 ]

The slub_debug is able to fix the corrupted slab freelist/page.
However, alloc_debug_processing() only checks the validity of current
and next freepointer during allocation path. As a result, once some
objects have their freepointers corrupted, deactivate_slab() may lead to
page fault.

Below is from a test kernel module when 'slub_debug=PUF,kmalloc-128
slub_nomerge'. The test kernel corrupts the freepointer of one free
object on purpose. Unfortunately, deactivate_slab() does not detect it
when iterating the freechain.

BUG: unable to handle page fault for address: 00000000123456f8
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
... ...
RIP: 0010:deactivate_slab.isra.92+0xed/0x490
... ...
Call Trace:
___slab_alloc+0x536/0x570
__slab_alloc+0x17/0x30
__kmalloc+0x1d9/0x200
ext4_htree_store_dirent+0x30/0xf0
htree_dirblock_to_tree+0xcb/0x1c0
ext4_htree_fill_tree+0x1bc/0x2d0
ext4_readdir+0x54f/0x920
iterate_dir+0x88/0x190
__x64_sys_getdents+0xa6/0x140
do_syscall_64+0x49/0x170
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Therefore, this patch adds extra consistency check in deactivate_slab().
Once an object's freepointer is corrupted, all following objects
starting at this object are isolated.

[akpm@linux-foundation.org: fix build with CONFIG_SLAB_DEBUG=n]
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Joe Jin <joe.jin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200331031450.12182-1-dongli.zhang@oracle.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/slub.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index b94ba8d35a025..473e0a8afb802 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -645,6 +645,20 @@ static void slab_fix(struct kmem_cache *s, char *fmt, ...)
va_end(args);
}

+static bool freelist_corrupted(struct kmem_cache *s, struct page *page,
+ void *freelist, void *nextfree)
+{
+ if ((s->flags & SLAB_CONSISTENCY_CHECKS) &&
+ !check_valid_pointer(s, page, nextfree)) {
+ object_err(s, page, freelist, "Freechain corrupt");
+ freelist = NULL;
+ slab_fix(s, "Isolate corrupted freechain");
+ return true;
+ }
+
+ return false;
+}
+
static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
{
unsigned int off; /* Offset of last byte */
@@ -1328,6 +1342,11 @@ static inline void inc_slabs_node(struct kmem_cache *s, int node,
static inline void dec_slabs_node(struct kmem_cache *s, int node,
int objects) {}

+static bool freelist_corrupted(struct kmem_cache *s, struct page *page,
+ void *freelist, void *nextfree)
+{
+ return false;
+}
#endif /* CONFIG_SLUB_DEBUG */

/*
@@ -2013,6 +2032,14 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
void *prior;
unsigned long counters;

+ /*
+ * If 'nextfree' is invalid, it is possible that the object at
+ * 'freelist' is already corrupted. So isolate all objects
+ * starting at 'freelist'.
+ */
+ if (freelist_corrupted(s, page, freelist, nextfree))
+ break;
+
do {
prior = page->freelist;
counters = page->counters;
--
2.25.1