Commit 52f23478 authored Jun 01, 2020 by Dongli Zhang Committed by Linus Torvalds Jun 02, 2020

mm/slub.c: fix corrupted freechain in deactivate_slab()



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>

parent 49f2d241

mm/slub.c

+27 −0

Original line number	Diff line number	Diff line
		@@ -679,6 +679,20 @@ 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 */
		@@ -1410,6 +1424,11 @@ 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 */

		/*
		@@ -2093,6 +2112,14 @@ 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;

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