On Thu, Mar 03, 2022 at 10:40:27PM +0800, Dongliang Mu wrote:
> From: Dongliang Mu <[email protected]>
>
> Syzbot reported a possible use-after-free in printing information
> in device_list_add.
>
> Very similar with the bug fixed by commit 0697d9a61099 ("btrfs: don't
> access possibly stale fs_info data for printing duplicate device"),
> but this time the use occurs in btrfs_info_in_rcu.
>
> ============================================================
> Call Trace:
> kasan_report.cold+0x83/0xdf mm/kasan/report.c:459
> btrfs_printk+0x395/0x425 fs/btrfs/super.c:244
> device_list_add.cold+0xd7/0x2ed fs/btrfs/volumes.c:957
> btrfs_scan_one_device+0x4c7/0x5c0 fs/btrfs/volumes.c:1387
> btrfs_control_ioctl+0x12a/0x2d0 fs/btrfs/super.c:2409
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:874 [inline]
> __se_sys_ioctl fs/ioctl.c:860 [inline]
> __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> ============================================================
>
> Fix this by modifying device->fs_info to NULL too.
>
> Reported-and-tested-by: [email protected]
> Signed-off-by: Dongliang Mu <[email protected]>
> ---
> fs/btrfs/volumes.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index b07d382d53a8..c1325bdae9a1 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -954,7 +954,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
> task_pid_nr(current));
> return ERR_PTR(-EEXIST);
> }
> - btrfs_info_in_rcu(device->fs_info,
> + btrfs_info_in_rcu(NULL,
A few lines above this is also NULL and was fixed by 0697d9a61099
("btrfs: don't access possibly stale fs_info data for printing duplicate
device"), so yeah we probably need the same here.
On 04/03/2022 02:24, David Sterba wrote:
> On Thu, Mar 03, 2022 at 10:40:27PM +0800, Dongliang Mu wrote:
>> From: Dongliang Mu <[email protected]>
>>
>> Syzbot reported a possible use-after-free in printing information
>> in device_list_add.
>>
>> Very similar with the bug fixed by commit 0697d9a61099 ("btrfs: don't
>> access possibly stale fs_info data for printing duplicate device"),
>> but this time the use occurs in btrfs_info_in_rcu.
>>
>> ============================================================
>> Call Trace:
>> kasan_report.cold+0x83/0xdf mm/kasan/report.c:459
>> btrfs_printk+0x395/0x425 fs/btrfs/super.c:244
>> device_list_add.cold+0xd7/0x2ed fs/btrfs/volumes.c:957
>> btrfs_scan_one_device+0x4c7/0x5c0 fs/btrfs/volumes.c:1387
>> btrfs_control_ioctl+0x12a/0x2d0 fs/btrfs/super.c:2409
>> vfs_ioctl fs/ioctl.c:51 [inline]
>> __do_sys_ioctl fs/ioctl.c:874 [inline]
>> __se_sys_ioctl fs/ioctl.c:860 [inline]
>> __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>> ============================================================
>>
>> Fix this by modifying device->fs_info to NULL too.
>>
>> Reported-and-tested-by: [email protected]
>> Signed-off-by: Dongliang Mu <[email protected]>
>> ---
>> fs/btrfs/volumes.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index b07d382d53a8..c1325bdae9a1 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -954,7 +954,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
>> task_pid_nr(current));
>> return ERR_PTR(-EEXIST);
>> }
>> - btrfs_info_in_rcu(device->fs_info,
>> + btrfs_info_in_rcu(NULL,
>
> A few lines above this is also NULL and was fixed by 0697d9a61099
> ("btrfs: don't access possibly stale fs_info data for printing duplicate
> device"), so yeah we probably need the same here.
So it appears that device->fs_info was garbage instead of NULL OR
fs_info->sb was NULL?
Because we always had a check if fs_info is null in btrfs_printk()
further the commit a0f6d924cada ("btrfs: remove stub device info from
messages when we have no fs_info") made it better.
Thanks, Anand
On Fri, Mar 04, 2022 at 07:53:27AM +0800, Anand Jain wrote:
> On 04/03/2022 02:24, David Sterba wrote:
> > On Thu, Mar 03, 2022 at 10:40:27PM +0800, Dongliang Mu wrote:
> >>
> >> Fix this by modifying device->fs_info to NULL too.
> >>
> >> Reported-and-tested-by: [email protected]
> >> Signed-off-by: Dongliang Mu <[email protected]>
> >> ---
> >> fs/btrfs/volumes.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> >> index b07d382d53a8..c1325bdae9a1 100644
> >> --- a/fs/btrfs/volumes.c
> >> +++ b/fs/btrfs/volumes.c
> >> @@ -954,7 +954,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
> >> task_pid_nr(current));
> >> return ERR_PTR(-EEXIST);
> >> }
> >> - btrfs_info_in_rcu(device->fs_info,
> >> + btrfs_info_in_rcu(NULL,
> >
> > A few lines above this is also NULL and was fixed by 0697d9a61099
> > ("btrfs: don't access possibly stale fs_info data for printing duplicate
> > device"), so yeah we probably need the same here.
>
> So it appears that device->fs_info was garbage instead of NULL OR
> fs_info->sb was NULL?
I think it's a warning that something could happen, in this case
potential garbage value of fs_info.
> Because we always had a check if fs_info is null in btrfs_printk()
> further the commit a0f6d924cada ("btrfs: remove stub device info from
> messages when we have no fs_info") made it better.
Yeah, that's removing a potential crash but still the NULL value could
come from a freed memory. Seems taht we can't rely on fs_info in
device_list_add at all and passing NULL is the only safe way.