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 fca33abd6c428..5c05a36bb746f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -644,6 +644,20 @@ 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 */ @@ -1379,6 +1393,11 @@ 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 */
/* @@ -2062,6 +2081,14 @@ 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;