Re: Out-of-bounds write in driver_override_show

[Greg Kroah-Hartman]

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...

Rest of the bug report below.

greg k-h


> 
> 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?).
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