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From: David Sterba <dsterba@suse.cz>
To: Qu Wenruo <wqu@suse.com>
Cc: linux-btrfs@vger.kernel.org, butt3rflyh4ck <butterflyhuangxx@gmail.com>
Subject: Re: [PATCH] btrfs: fix NULL pointer dereference when deleting device by invalid id
Date: Tue, 10 Aug 2021 16:23:23 +0200	[thread overview]
Message-ID: <20210810142323.GX5047@twin.jikos.cz> (raw)
In-Reply-To: <20210806102415.304717-1-wqu@suse.com>

On Fri, Aug 06, 2021 at 06:24:15PM +0800, Qu Wenruo wrote:
> [BUG]
> It's super easy to trigger NULL pointer dereference, just by removing a
> non-exist device id:
> 
>  # mkfs.btrfs -f -m single -d single /dev/test/scratch1 \
> 				     /dev/test/scratch2
>  # mount /dev/test/scratch1 /mnt/btrfs
>  # btrfs device remove 3 /mnt/btrfs
> 
> Then we have the following kernel NULL pointer dereference:
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000000
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] PREEMPT SMP NOPTI
>  CPU: 9 PID: 649 Comm: btrfs Not tainted 5.14.0-rc3-custom+ #35
>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
>  RIP: 0010:btrfs_rm_device+0x4de/0x6b0 [btrfs]
>   btrfs_ioctl+0x18bb/0x3190 [btrfs]
>   ? lock_is_held_type+0xa5/0x120
>   ? find_held_lock.constprop.0+0x2b/0x80
>   ? do_user_addr_fault+0x201/0x6a0
>   ? lock_release+0xd2/0x2d0
>   ? __x64_sys_ioctl+0x83/0xb0
>   __x64_sys_ioctl+0x83/0xb0
>   do_syscall_64+0x3b/0x90
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> [CAUSE]
> Commit a27a94c2b0c7 ("btrfs: Make btrfs_find_device_by_devspec return
> btrfs_device directly") moves the "missing" device path check into
> btrfs_rm_device().
> 
> But btrfs_rm_device() itself can have case where it only receives
> @devid, with NULL as @device_path.
> 
> In that case, calling strcmp() on NULL will trigger the NULL pointer
> dereference.
> 
> Before that commit, we handle the "missing" case inside
> btrfs_find_device_by_devspec(), which will not check @device_path at all
> if @devid is provided, thus no way to trigger the bug.
> 
> [FIX]
> Before calling strcmp(), also make sure @device_path is not NULL.
> 
> Fixes: a27a94c2b0c7 ("btrfs: Make btrfs_find_device_by_devspec return btrfs_device directly")
> Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Thanks for the report and fix, added to misc-next.

  reply	other threads:[~2021-08-10 14:26 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-06 10:24 [PATCH] btrfs: fix NULL pointer dereference when deleting device by invalid id Qu Wenruo
2021-08-10 14:23 ` David Sterba [this message]
2021-08-10 15:57 ` Anand Jain

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