[+CC Christoph, linux-mm] On 04/17/2016 07:29 PM, Alexei Starovoitov wrote: > On Sun, Apr 17, 2016 at 12:58:21PM -0400, Sasha Levin wrote: >> Hi all, >> >> I've hit the following while fuzzing with syzkaller inside a KVM tools guest >> running the latest -next kernel: > > thanks for the report. Adding Tejun... Looks like this report died, and meanwhile there's a CVE for it, including a reproducer: http://seclists.org/oss-sec/2016/q2/332 So maybe we should fix it now? :) > if I read the report correctly it's not about bpf, but rather points to > the issue inside percpu logic. > First __alloc_percpu_gfp() is called, then the memory is freed with > free_percpu() which triggers async pcpu_balance_work and then > pcpu_extend_area_map is hitting use-after-free. > I guess bpf percpu array map is stressing this logic the most. I've been staring at it for a while (not knowing the code at all) and the first thing that struck me is that pcpu_extend_area_map() is done outside of pcpu_lock. So what prevents the chunk from being freed during the extend? > Any simpler steps to reproduce ? > >> [ 2590.845375] ================================================================== >> >> [ 2590.845445] BUG: KASAN: use-after-free in pcpu_extend_area_map+0x8a/0x130 at addr ffff88035452a3cc >> >> [ 2590.845457] Read of size 4 by task syz-executor/31307 >> >> [ 2590.845464] ============================================================================= >> >> [ 2590.845476] BUG kmalloc-128 (Tainted: G W ): kasan: bad access detected >> >> [ 2590.845479] ----------------------------------------------------------------------------- >> >> [ 2590.845479] >> >> [ 2590.845485] Disabling lock debugging due to kernel taint >> >> [ 2590.845496] INFO: Allocated in 0xbbbbbbbbbbbbbbbb age=18446609615465671625 cpu=0 pid=0 >> >> [ 2590.845504] pcpu_mem_zalloc+0x7e/0xc0 >> >> [ 2590.845521] ___slab_alloc+0x7af/0x870 >> >> [ 2590.845528] __slab_alloc.isra.22+0xf4/0x130 >> >> [ 2590.845535] __kmalloc+0x1fe/0x340 >> >> [ 2590.845543] pcpu_mem_zalloc+0x7e/0xc0 >> >> [ 2590.845551] pcpu_create_chunk+0x79/0x600 >> >> [ 2590.845558] pcpu_alloc+0x5d4/0xe10 >> >> [ 2590.845567] __alloc_percpu_gfp+0x27/0x30 >> >> [ 2590.845582] array_map_alloc+0x595/0x710 >> >> [ 2590.845590] SyS_bpf+0x336/0xba0 >> >> [ 2590.845605] do_syscall_64+0x2a6/0x4a0 >> >> [ 2590.845639] return_from_SYSCALL_64+0x0/0x6a >> >> [ 2590.845647] INFO: Freed in 0x10022ebb3 age=18446628393062689737 cpu=0 pid=0 >> >> [ 2590.845653] kvfree+0x45/0x50 >> >> [ 2590.845660] __slab_free+0x6a/0x2f0 >> >> [ 2590.845665] kfree+0x22c/0x270 >> >> [ 2590.845671] kvfree+0x45/0x50 >> >> [ 2590.845680] pcpu_balance_workfn+0x11a1/0x1280 >> >> [ 2590.845693] process_one_work+0x973/0x10b0 >> >> [ 2590.845700] worker_thread+0xcfd/0x1160 >> >> [ 2590.845708] kthread+0x2e7/0x300 >> >> [ 2590.845716] ret_from_fork+0x22/0x40 >> >> [ 2590.845724] INFO: Slab 0xffffea000d514a00 objects=35 used=33 fp=0xffff88035452b740 flags=0x2fffff80004080 >> >> [ 2590.845730] INFO: Object 0xffff88035452a3a0 @offset=9120 fp=0xbbbbbbbbbbbbbbbb >> >> [ 2590.845730] >> >> [ 2590.845743] Redzone ffff88035452a398: 00 00 00 00 00 00 00 00 ........ >> >> [ 2590.845751] Object ffff88035452a3a0: bb bb bb bb bb bb bb bb 00 00 00 00 00 00 00 00 ................ >> >> [ 2590.845758] Object ffff88035452a3b0: b0 7b 17 3f 03 88 ff ff 00 00 08 00 00 00 08 00 .{.?............ >> >> [ 2590.845765] Object ffff88035452a3c0: 00 00 e0 f9 ff e8 ff ff 01 00 00 00 10 00 00 00 ................ >> >> [ 2590.845775] Object ffff88035452a3d0: 18 83 2c 3f 03 88 ff ff e0 ff ff ff 0f 00 00 00 ..,?............ >> >> [ 2590.845783] Object ffff88035452a3e0: e0 a3 52 54 03 88 ff ff e0 a3 52 54 03 88 ff ff ..RT......RT.... >> >> [ 2590.845790] Object ffff88035452a3f0: 90 96 6b 9f ff ff ff ff e8 a7 13 3f 03 88 ff ff ..k........?.... >> >> [ 2590.845797] Object ffff88035452a400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ >> >> [ 2590.845804] Object ffff88035452a410: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ >> >> [ 2590.845811] Redzone ffff88035452a420: 00 00 00 00 00 00 00 00 ........ >> >> [ 2590.845818] Padding ffff88035452a558: b5 eb 22 00 01 00 00 00 .."..... >> >> [ 2590.845833] CPU: 0 PID: 31307 Comm: syz-executor Tainted: G B W 4.6.0-rc3-next-20160412-sasha-00023-g0b02d6d-dirty #2998 >> >> [ 2590.845851] 0000000000000000 00000000a66f8039 ffff880354f8fa60 ffffffffa0fc9d01 >> >> [ 2590.845861] ffffffff00000000 fffffbfff57ad2a0 0000000041b58ab3 ffffffffab65eee0 >> >> [ 2590.845870] ffffffffa0fc9b88 00000000a66f8039 ffff88035e9d4000 ffffffffab67cede >> >> [ 2590.845872] Call Trace: >> >> [ 2590.845903] dump_stack (lib/dump_stack.c:53) >> [ 2590.845939] print_trailer (mm/slub.c:668) >> [ 2590.845948] object_err (mm/slub.c:675) >> [ 2590.845958] kasan_report_error (mm/kasan/report.c:180 mm/kasan/report.c:276) >> [ 2590.846007] __asan_report_load4_noabort (mm/kasan/report.c:318) >> [ 2590.846028] pcpu_extend_area_map (mm/percpu.c:445) This line is: if (new_alloc <= chunk->map_alloc) i.e. the first time the function touches some part of the chunk object. >> [ 2590.846038] pcpu_alloc (mm/percpu.c:940) >> [ 2590.846128] __alloc_percpu_gfp (mm/percpu.c:1068) >> [ 2590.846140] array_map_alloc (kernel/bpf/arraymap.c:36 kernel/bpf/arraymap.c:99) >> [ 2590.846150] SyS_bpf (kernel/bpf/syscall.c:35 kernel/bpf/syscall.c:183 kernel/bpf/syscall.c:830 kernel/bpf/syscall.c:787) >> [ 2590.846203] do_syscall_64 (arch/x86/entry/common.c:350) >> [ 2590.846214] entry_SYSCALL64_slow_path (arch/x86/entry/entry_64.S:251) >> [ 2590.846217] Memory state around the buggy address: >> >> [ 2590.846224] ffff88035452a280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> >> [ 2590.846230] ffff88035452a300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> >> [ 2590.846237] >ffff88035452a380: fc fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb >> >> [ 2590.846240] ^ >> >> [ 2590.846247] ffff88035452a400: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc >> >> [ 2590.846253] ffff88035452a480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> >> [ 2590.846256] ================================================================== >> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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