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Date: Mon, 1 Dec 2014 23:20:12 +0400 From: Dmitry Vyukov <dvyukov@...gle.com> To: Alex Williamson <alex.williamson@...hat.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, kasan-dev <kasan-dev@...glegroups.com>, LKML <linux-kernel@...r.kernel.org>, Kostya Serebryany <kcc@...gle.com>, Dmitry Chernenkov <dmitryc@...gle.com>, Andrey Konovalov <andreyknvl@...gle.com>, Greg Thelen <gthelen@...gle.com>, Kees Cook <keescook@...gle.com>, Robert Swiecki <swiecki@...gle.com>, Andrey Ryabinin <a.ryabinin@...sung.com>, Konstantin Khlebnikov <koct9i@...il.com>, Yury Gribov <y.gribov@...sung.com> Subject: Re: Out-of-bounds write in driver_override_show On Mon, Dec 1, 2014 at 10:12 PM, Alex Williamson <alex.williamson@...hat.com> wrote: > On Sat, 2014-11-29 at 10:05 -0800, Greg Kroah-Hartman wrote: >> On Sat, Nov 29, 2014 at 01:38:10PM +0400, Dmitry Vyukov wrote: >> > Hello, >> > >> > I am working on Kernel AddressSanitizer, a fast memory error detector >> > for kernel: >> > https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel >> > >> > Here is an error report that I got while running trinity: >> >> Alex, this looks like the code you added, you need to properly check for >> the size of the string before writing it back... > > Thanks for the report, I'm not sure I entirely understand the issue > though. The string at pci_dev.driver_override is bounds checked when > set in driver_override_store() and I think that the buffer for a sysfs > show is always a page, right? So by checking strlen are we just > guarding against some in-kernel setting of driver_override other than > the _store() path? Thanks, Hi! driver_override_store checks it against PATH_MAX, and PATH_MAX is generally unrelated to PAGE_SIZE. It happens so that in my config PATH_MAX==PAGE_SIZE. Yet, the sprintf writes PAGE_SIZE+1 (+1 for the trailing 0 terminator). So even if PATH_MAX==PAGE_SIZE it smashes the first byte of the next memory block. >> > BUG: AddressSanitizer: out of bounds access in vsnprintf+0xd0/0x890 at >> > addr ffff880057483261 >> > Write of size 1 by task trinity-c54/4461 >> > ============================================================================= >> > BUG kmalloc-4096 (Tainted: G W ): kasan error >> > ----------------------------------------------------------------------------- >> > INFO: Allocated in seq_open+0x5a/0xe0 age=1571449 cpu=0 pid=28869 >> > __slab_alloc+0x4c4/0x4e0 >> > __kmalloc+0x18b/0x1b0 >> > seq_buf_alloc+0x16/0x40 >> > traverse+0x243/0x350 >> > seq_read+0x434/0x6b0 >> > kernfs_fop_read+0x176/0x1f0 >> > vfs_read+0xd7/0x240 >> > SyS_read+0x57/0xc0 >> > system_call_fastpath+0x12/0x17 >> > INFO: Slab 0xffffea00015d2000 objects=7 used=7 fp=0x (null) >> > flags=0x100000000004080 >> > INFO: Object 0xffff880057482260 @offset=8800 fp=0xffffffffffffffff >> > >> > CPU: 0 PID: 4461 Comm: trinity-c54 Tainted: G B W 3.18.0-rc1+ #8 >> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> > ffffffff81fbdaac ffff88008e3ab8c8 ffffffff81c85c3f 0000000000001130 >> > ffff88011b003200 ffff88008e3ab8f8 ffffffff811ee018 ffff88011b003200 >> > ffffea00015d2000 ffff880057482260 ffff8800d748225f ffff88008e3ab928 >> > Call Trace: >> > [<ffffffff811f76a5>] __asan_store1+0x75/0xb0 mm/kasan/kasan.c:417 >> > [<ffffffff8147b660>] vsnprintf+0xd0/0x890 lib/vsprintf.c:1860 >> > [<ffffffff8147bf70>] sprintf+0x40/0x50 lib/vsprintf.c:1989 >> > [<ffffffff816e1e51>] driver_override_show+0x31/0x40 drivers/base/platform.c:755 >> > [<ffffffff816d92d9>] dev_attr_show+0x39/0x80 drivers/base/core.c:120 >> > [<ffffffff812a3892>] sysfs_kf_seq_show+0x152/0x230 fs/sysfs/file.c:63 >> > [<ffffffff812a13a6>] kernfs_seq_show+0x76/0x90 fs/kernfs/file.c:168 >> > [<ffffffff8122f755>] traverse+0x185/0x350 fs/seq_file.c:120 >> > [<ffffffff8122fee4>] seq_read+0x434/0x6b0 fs/seq_file.c:191 >> > [<ffffffff812a22f6>] kernfs_fop_read+0x176/0x1f0 fs/kernfs/file.c:244 >> > [<ffffffff811fc131>] do_loop_readv_writev+0x71/0xa0 fs/read_write.c:708 >> > [<ffffffff811fe850>] do_readv_writev+0x350/0x360 fs/read_write.c:842 >> > [<ffffffff811fe8ab>] vfs_readv+0x4b/0x70 fs/read_write.c:867 >> > [< inlined >] SyS_preadv+0xca/0xf0 SYSC_preadv fs/read_write.c:945 >> > [<ffffffff811fec0a>] SyS_preadv+0xca/0xf0 fs/read_write.c:931 >> > [<ffffffff81c91f69>] system_call_fastpath+0x12/0x17 >> > arch/x86/kernel/entry_64.S:422 >> > Memory state around the buggy address: >> > ffff880057482f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ffff880057483000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ffff880057483080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ffff880057483100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ffff880057483180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > >ffff880057483200: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc >> > ^ >> > ffff880057483280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> > ffff880057483300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> > ffff880057483380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ffff880057483400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ffff880057483480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> > ================================================================== >> > dev_attr_show: driver_override_show+0x0/0x40 returned bad count >> > fill_read_buffer: dev_attr_show+0x0/0x80 returned bad count >> > >> > >> > My source is on revision f114040e3ea6e07372334ade75d1ee0775c355e1. >> > >> > I've looked at source code and it seems that driver_override_store >> > does not do length sanitization, so driver_override_show smashes >> > subsequent memory blocks in sprinf (with user-provided data?). > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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