On Wed, Jul 31, 2019 at 12:39 AM Laura Abbott <labb...@redhat.com> wrote: > > On 7/29/19 5:43 AM, kernel test robot wrote: > > FYI, we noticed the following commit (built with gcc-7): > > > > commit: 6471384af2a6530696fc0203bafe4de41a23c9ef ("mm: security: introduce > > init_on_alloc=1 and init_on_free=1 boot options") > > https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux.git > > master > > > > in testcase: trinity > > with following parameters: > > > > runtime: 300s > > > > test-description: Trinity is a linux system call fuzz tester. > > test-url: http://codemonkey.org.uk/projects/trinity/ > > > > > > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m > > 8G > > > > caused below changes (please refer to attached dmesg/kmsg for entire > > log/backtrace): > > > > > > +------------------------------------------+------------+------------+ > > | | ba5c5e4a5d | 6471384af2 | > > +------------------------------------------+------------+------------+ > > | boot_successes | 8 | 0 | > > | boot_failures | 2 | 15 | > > | invoked_oom-killer:gfp_mask=0x | 1 | | > > | Mem-Info | 1 | | > > | kernel_BUG_at_security/keys/keyring.c | 1 | | > > | invalid_opcode:#[##] | 1 | 15 | > > | RIP:__key_link_begin | 1 | | > > | Kernel_panic-not_syncing:Fatal_exception | 1 | 15 | > > | kernel_BUG_at_mm/slub.c | 0 | 15 | > > | RIP:kfree | 0 | 15 | > > +------------------------------------------+------------+------------+ > > > > > > If you fix the issue, kindly add following tag > > Reported-by: kernel test robot <rong.a.c...@intel.com> > > > > > > [ 4.478342] kernel BUG at mm/slub.c:306! > > [ 4.482437] invalid opcode: 0000 [#1] PREEMPT PTI > > [ 4.485750] CPU: 0 PID: 0 Comm: swapper Not tainted > > 5.2.0-05754-g6471384a #4 > > [ 4.490635] RIP: 0010:kfree+0x58a/0x5c0 > > [ 4.493679] Code: 48 83 05 78 37 51 02 01 0f 0b 48 83 05 7e 37 51 02 01 > > 48 83 05 7e 37 51 02 01 48 83 05 7e 37 51 02 01 48 83 05 d6 37 51 02 01 > > <0f> 0b 48 83 05 d4 37 51 02 01 48 83 05 d4 37 51 02 01 48 83 05 d4 > > [ 4.506827] RSP: 0000:ffffffff82603d90 EFLAGS: 00010002 > > [ 4.510475] RAX: ffff8c3976c04320 RBX: ffff8c3976c04300 RCX: > > 0000000000000000 > > [ 4.515420] RDX: ffff8c3976c04300 RSI: 0000000000000000 RDI: > > ffff8c3976c04320 > > [ 4.520331] RBP: ffffffff82603db8 R08: 0000000000000000 R09: > > 0000000000000000 > > [ 4.525288] R10: ffff8c3976c04320 R11: ffffffff8289e1e0 R12: > > ffffd52cc8db0100 > > [ 4.530180] R13: ffff8c3976c01a00 R14: ffffffff810f10d4 R15: > > ffff8c3976c04300 > > [ 4.535079] FS: 0000000000000000(0000) GS:ffffffff8266b000(0000) > > knlGS:0000000000000000 > > [ 4.540628] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 4.544593] CR2: ffff8c397ffff000 CR3: 0000000125020000 CR4: > > 00000000000406b0 > > [ 4.549558] Call Trace: > > [ 4.551266] apply_wqattrs_prepare+0x154/0x280 > > [ 4.554357] apply_workqueue_attrs_locked+0x4e/0xe0 > > [ 4.557728] apply_workqueue_attrs+0x36/0x60 > > [ 4.560654] alloc_workqueue+0x25a/0x6d0 > > [ 4.563381] ? kmem_cache_alloc_trace+0x1e3/0x500 > > [ 4.566628] ? __mutex_unlock_slowpath+0x44/0x3f0 > > [ 4.569875] workqueue_init_early+0x246/0x348 > > [ 4.573025] start_kernel+0x3c7/0x7ec > > [ 4.575558] x86_64_start_reservations+0x40/0x49 > > [ 4.578738] x86_64_start_kernel+0xda/0xe4 > > [ 4.581600] secondary_startup_64+0xb6/0xc0 > > [ 4.584473] Modules linked in: > > [ 4.586620] ---[ end trace f67eb9af4d8d492b ]--- > > I think this is catching an edge case with the freelist walking code > in slab_free_freelist_hook. If we're not doing a bulk free, > getting the free pointer from the object is going to be bogus so > there's a chance it could trigger the bug in set_freepointer even > if we don't actually care about it since it's going to get > overwritten when we actually free. It's probably more robust > to make sure we're terminating it with NULL. Lightly tested: I see, my understanding was that it's safe to write the value we've previously read with get_freepointer(). But chances are that the random data from this pointer simply matches the object pointer.
> diff --git a/mm/slub.c b/mm/slub.c > index e6c030e47364..8834563cdb4b 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1432,7 +1432,9 @@ 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)) > + if (slab_want_init_on_free(s)) { > + void *p = NULL; > + > do { > object = next; > next = get_freepointer(s, object); > @@ -1445,8 +1447,10 @@ 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, next); > + set_freepointer(s, object, p); > + p = object; > } while (object != old_tail); > + } > > /* > * Compiler cannot detect this function can be removed if slab_free_hook() > This one looks good, care to send a patch? Otherwise I can do that for you. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg