Re: [PATCH v4] xfs: fix exception caused by unexpected illegal bestcount in leaf dir

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Oct 07, 2022 at 07:33:53PM +0800, Guo Xuenan wrote:
> 
> On 2022/9/30 4:50, Darrick J. Wong wrote:
> > On Thu, Sep 29, 2022 at 04:51:55PM +0800, Guo Xuenan wrote:
> > > For leaf dir, In most cases, there should be as many bestfree slots
> > > as the dir data blocks that can fit under i_size (except for [1]).
> > > 
> > > Root cause is we don't examin the number bestfree slots, when the slots
> > > number less than dir data blocks, if we need to allocate new dir data
> > > block and update the bestfree array, we will use the dir block number as
> > > index to assign bestfree array, while we did not check the leaf buf
> > > boundary which may cause UAF or other memory access problem. This issue
> > > can also triggered with test cases xfs/473 from fstests.
> > > 
> > > According to Dave Chinner & Darrick's suggestion, adding buffer verifier
> > > to detect this abnormal situation in time.
> > > Simplify the testcase for fstest xfs/554 [1]
> > > 
> > > The error log is shown as follows:
> > > ==================================================================
> > > BUG: KASAN: use-after-free in xfs_dir2_leaf_addname+0x1995/0x1ac0
> > > Write of size 2 at addr ffff88810168b000 by task touch/1552
> > > CPU: 5 PID: 1552 Comm: touch Not tainted 6.0.0-rc3+ #101
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > > 1.13.0-1ubuntu1.1 04/01/2014
> > > Call Trace:
> > >   <TASK>
> > >   dump_stack_lvl+0x4d/0x66
> > >   print_report.cold+0xf6/0x691
> > >   kasan_report+0xa8/0x120
> > >   xfs_dir2_leaf_addname+0x1995/0x1ac0
> > >   xfs_dir_createname+0x58c/0x7f0
> > >   xfs_create+0x7af/0x1010
> > >   xfs_generic_create+0x270/0x5e0
> > >   path_openat+0x270b/0x3450
> > >   do_filp_open+0x1cf/0x2b0
> > >   do_sys_openat2+0x46b/0x7a0
> > >   do_sys_open+0xb7/0x130
> > >   do_syscall_64+0x35/0x80
> > >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > > RIP: 0033:0x7fe4d9e9312b
> > > Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0
> > > 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00
> > > f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 33 0c 25
> > > RSP: 002b:00007ffda4c16c20 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> > > RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe4d9e9312b
> > > RDX: 0000000000000941 RSI: 00007ffda4c17f33 RDI: 00000000ffffff9c
> > > RBP: 00007ffda4c17f33 R08: 0000000000000000 R09: 0000000000000000
> > > R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000941
> > > R13: 00007fe4d9f631a4 R14: 00007ffda4c17f33 R15: 0000000000000000
> > >   </TASK>
> > > 
> > > The buggy address belongs to the physical page:
> > > page:ffffea000405a2c0 refcount:0 mapcount:0 mapping:0000000000000000
> > > index:0x0 pfn:0x10168b
> > > flags: 0x2fffff80000000(node=0|zone=2|lastcpupid=0x1fffff)
> > > raw: 002fffff80000000 ffffea0004057788 ffffea000402dbc8 0000000000000000
> > > raw: 0000000000000000 0000000000170000 00000000ffffffff 0000000000000000
> > > page dumped because: kasan: bad access detected
> > > 
> > > Memory state around the buggy address:
> > >   ffff88810168af00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > >   ffff88810168af80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > > ffff88810168b000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > >                     ^
> > >   ffff88810168b080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > >   ffff88810168b100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > > ==================================================================
> > > Disabling lock debugging due to kernel taint
> > > 00000000: 58 44 44 33 5b 53 35 c2 00 00 00 00 00 00 00 78
> > > XDD3[S5........x
> > > XFS (sdb): Internal error xfs_dir2_data_use_free at line 1200 of file
> > > fs/xfs/libxfs/xfs_dir2_data.c.  Caller
> > > xfs_dir2_data_use_free+0x28a/0xeb0
> > > CPU: 5 PID: 1552 Comm: touch Tainted: G    B              6.0.0-rc3+
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > > 1.13.0-1ubuntu1.1 04/01/2014
> > > Call Trace:
> > >   <TASK>
> > >   dump_stack_lvl+0x4d/0x66
> > >   xfs_corruption_error+0x132/0x150
> > >   xfs_dir2_data_use_free+0x198/0xeb0
> > >   xfs_dir2_leaf_addname+0xa59/0x1ac0
> > >   xfs_dir_createname+0x58c/0x7f0
> > >   xfs_create+0x7af/0x1010
> > >   xfs_generic_create+0x270/0x5e0
> > >   path_openat+0x270b/0x3450
> > >   do_filp_open+0x1cf/0x2b0
> > >   do_sys_openat2+0x46b/0x7a0
> > >   do_sys_open+0xb7/0x130
> > >   do_syscall_64+0x35/0x80
> > >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > > RIP: 0033:0x7fe4d9e9312b
> > > Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0
> > > 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00
> > > f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 33 0c 25
> > > RSP: 002b:00007ffda4c16c20 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> > > RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe4d9e9312b
> > > RDX: 0000000000000941 RSI: 00007ffda4c17f46 RDI: 00000000ffffff9c
> > > RBP: 00007ffda4c17f46 R08: 0000000000000000 R09: 0000000000000001
> > > R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000941
> > > R13: 00007fe4d9f631a4 R14: 00007ffda4c17f46 R15: 0000000000000000
> > >   </TASK>
> > > XFS (sdb): Corruption detected. Unmount and run xfs_repair
> > > 
> > > [1] https://lore.kernel.org/all/20220928095355.2074025-1-guoxuenan@huawei.com/
> > > Reviewed-by: Hou Tao <houtao1@huawei.com>
> > > Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
> > > ---
> > >   fs/xfs/libxfs/xfs_dir2_leaf.c | 4 ++++
> > >   1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_dir2_leaf.c b/fs/xfs/libxfs/xfs_dir2_leaf.c
> > > index d9b66306a9a7..bf4633b228cd 100644
> > > --- a/fs/xfs/libxfs/xfs_dir2_leaf.c
> > > +++ b/fs/xfs/libxfs/xfs_dir2_leaf.c
> > > @@ -146,6 +146,7 @@ xfs_dir3_leaf_check_int(
> > >   	xfs_dir2_leaf_tail_t		*ltp;
> > >   	int				stale;
> > >   	int				i;
> > > +	xfs_dir2_db_t			db;
> > >   	ltp = xfs_dir2_leaf_tail_p(geo, leaf);
> > > @@ -175,6 +176,9 @@ xfs_dir3_leaf_check_int(
> > >   		}
> > >   		if (hdr->ents[i].address == cpu_to_be32(XFS_DIR2_NULL_DATAPTR))
> > >   			stale++;
> > > +		db = xfs_dir2_dataptr_to_db(geo, be32_to_cpu(hdr->ents[i].address));
> > > +		if (db >= be32_to_cpu(ltp->bestcount))
> > > +			return __this_address;
> > What about LEAFN blocks?  Those don't have a bests[] array or a
> > bestcount because the free space info is in the third directory
> > partition, so there's nothing to check here.  IIUC, only LEAF1 blocks
> > can compare bestcount to the entry addresses, right?
> Hi, Darrick:
> 
> Sorry for the late reply, I was on vacation last week.I have confirmed it,
> you're right,may we
> need add an additional restriction, compare only LEAF1 block.
> 
> According to the problem you pointed out, amend as below. Looking forward
> for your valuable suggestions :)
> 
> diff --git a/fs/xfs/libxfs/xfs_dir2_leaf.c b/fs/xfs/libxfs/xfs_dir2_leaf.c
> index d9b66306a9a7..cd9ff1322445 100644
> --- a/fs/xfs/libxfs/xfs_dir2_leaf.c
> +++ b/fs/xfs/libxfs/xfs_dir2_leaf.c
> @@ -175,6 +175,12 @@ xfs_dir3_leaf_check_int(
>                 }
>                 if (hdr->ents[i].address ==
> cpu_to_be32(XFS_DIR2_NULL_DATAPTR))
>                         stale++;
> +               if ((hdr->magic == XFS_DIR2_LEAF1_MAGIC ||
> +                       hdr->magic == XFS_DIR3_LEAF1_MAGIC) &&
> +                       xfs_dir2_dataptr_to_db(geo,
> + be32_to_cpu(hdr->ents[i].address))
> +                                       >= be32_to_cpu(ltp->bestcount))
> +                       return __this_address;

That looks like a reasonable amendment to the code, though you might
hoist the leaf1 detection to a local variable so that we don't have to
do the same comparison multiple times in the same function.

	bool isleaf1 = (hdr->magic == XFS_DIR2_LEAF1_MAGIC ||
			hdr->magic == XFS_DIR3_LEAF1_MAGIC);

	/* Leaves and bests don't overlap in leaf format. */
	if (isleaf1 &&
	    (char *)&hdr->ents[hdr->count] > (char *)xfs_dir2_leaf_bests_p(ltp))
		return __this_address;

	...

		if (isleaf1 &&
		    xfs_dir2_dataptr_to_db(geo,
					be32_to_cpu(hdr->ents[i].address)) >=
					be32_to_cpu(ltp->bestcount))
				return __this_address;

Or something like that.

--D

>         }
>         if (hdr->stale != stale)
>                 return __this_address;
> 
> 
> 
> Thanks
> Xuenan
> > --D
> > 
> > >   	}
> > >   	if (hdr->stale != stale)
> > >   		return __this_address;
> > > -- 
> > > 2.25.1
> > > 
> > .
> 
> -- 
> Guo Xuenan
> -----------------------------
> Email: guoxuenan@huawei.com
>