Re: KASAN: slab-out-of-bounds Read in qrtr_endpoint_post

[Manivannan Sadhasivam]

Hi Bjorn,

On Sat, Jun 27, 2020 at 01:57:13PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    1590a2e1 Merge tag 'acpi-5.8-rc3' of git://git.kernel.org/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14b2b503100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bf3aec367b9ab569
> dashboard link: https://syzkaller.appspot.com/bug?extid=b8fe393f999a291a9ea6
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=109e6b55100000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13671a3d100000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b8fe393f999a291a9ea6@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in qrtr_endpoint_post+0xeeb/0x1010 net/qrtr/qrtr.c:462
> Read of size 2 at addr ffff88809de50c48 by task syz-executor531/6806
> 
> CPU: 0 PID: 6806 Comm: syz-executor531 Not tainted 5.8.0-rc2-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x18f/0x20d lib/dump_stack.c:118
>  print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
>  __kasan_report mm/kasan/report.c:513 [inline]
>  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
>  qrtr_endpoint_post+0xeeb/0x1010 net/qrtr/qrtr.c:462
>  qrtr_tun_write_iter+0xf5/0x180 net/qrtr/tun.c:92

Hmm. Is this due to the fact that we are not checking the length of the
kbuf allocated in qrtr_tun_write_iter()? The length derived from
'iov_iter_count(from)' gets used directly and that might be causing the
out of bound access error here.

Thanks,
Mani

>  call_write_iter include/linux/fs.h:1907 [inline]
>  do_iter_readv_writev+0x567/0x780 fs/read_write.c:694
>  do_iter_write+0x188/0x5f0 fs/read_write.c:999
>  compat_writev+0x1ea/0x390 fs/read_write.c:1352
>  do_compat_pwritev64+0x180/0x1b0 fs/read_write.c:1401
>  do_syscall_32_irqs_on+0x3f/0x60 arch/x86/entry/common.c:403
>  __do_fast_syscall_32 arch/x86/entry/common.c:448 [inline]
>  do_fast_syscall_32+0x7f/0x120 arch/x86/entry/common.c:474
>  entry_SYSENTER_compat+0x6d/0x7c arch/x86/entry/entry_64_compat.S:138
> RIP: 0023:0xf7f8f569
> Code: Bad RIP value.
> RSP: 002b:00000000ffda5ffc EFLAGS: 00000292 ORIG_RAX: 000000000000014e
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020000440
> RDX: 0000000000000001 RSI: 0000000000000000 RDI: 00000000080bb528
> RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 6806:
>  save_stack+0x1b/0x40 mm/kasan/common.c:48
>  set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
>  __do_kmalloc mm/slab.c:3656 [inline]
>  __kmalloc+0x17a/0x340 mm/slab.c:3665
>  kmalloc include/linux/slab.h:560 [inline]
>  kzalloc include/linux/slab.h:669 [inline]
>  qrtr_tun_write_iter+0x8a/0x180 net/qrtr/tun.c:83
>  call_write_iter include/linux/fs.h:1907 [inline]
>  do_iter_readv_writev+0x567/0x780 fs/read_write.c:694
>  do_iter_write+0x188/0x5f0 fs/read_write.c:999
>  compat_writev+0x1ea/0x390 fs/read_write.c:1352
>  do_compat_pwritev64+0x180/0x1b0 fs/read_write.c:1401
>  do_syscall_32_irqs_on+0x3f/0x60 arch/x86/entry/common.c:403
>  __do_fast_syscall_32 arch/x86/entry/common.c:448 [inline]
>  do_fast_syscall_32+0x7f/0x120 arch/x86/entry/common.c:474
>  entry_SYSENTER_compat+0x6d/0x7c arch/x86/entry/entry_64_compat.S:138
> 
> Freed by task 1:
>  save_stack+0x1b/0x40 mm/kasan/common.c:48
>  set_track mm/kasan/common.c:56 [inline]
>  kasan_set_free_info mm/kasan/common.c:316 [inline]
>  __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
>  __cache_free mm/slab.c:3426 [inline]
>  kfree+0x103/0x2c0 mm/slab.c:3757
>  tomoyo_path_perm+0x234/0x3f0 security/tomoyo/file.c:842
>  security_inode_getattr+0xcf/0x140 security/security.c:1278
>  vfs_getattr fs/stat.c:121 [inline]
>  vfs_statx+0x170/0x390 fs/stat.c:206
>  vfs_lstat include/linux/fs.h:3301 [inline]
>  __do_sys_newlstat+0x91/0x110 fs/stat.c:374
>  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff88809de50c40
>  which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 8 bytes inside of
>  32-byte region [ffff88809de50c40, ffff88809de50c60)
> The buggy address belongs to the page:
> page:ffffea0002779400 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88809de50fc1
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea000277e008 ffffea0002761c88 ffff8880aa0001c0
> raw: ffff88809de50fc1 ffff88809de50000 000000010000003f 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff88809de50b00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>  ffff88809de50b80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> >ffff88809de50c00: fb fb fb fb fc fc fc fc 04 fc fc fc fc fc fc fc
>                                               ^
>  ffff88809de50c80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>  ffff88809de50d00: fb fb fb fb fc fc fc fc 00 01 fc fc fc fc fc fc
> ==================================================================
>