Re: [PATCH] floppy: fix lock_fdc() signal handling

[Dmitry Vyukov <dvyukov@google.com>]

On Thu, Jan 28, 2016 at 11:43 AM, Jiri Kosina <jikos@kernel.org> wrote:
> On Thu, 28 Jan 2016, Dmitry Vyukov wrote:
>
>> I have not seen any /dev/fd0 related crashes over night. Previously I
>> seen tons of them, so I guess this bug is fixed.
>> Please send this upstream.
>> Thanks
>
> Thanks a lot for testing, Dmitry.
>
> Jens, here is the patch with proper changelog. Could you please apply it
> to your tree? Or would you prefer a pull request with this single patch in
> it?
> Thanks.


Done
Replaced the old patch with this one.
Thanks for a quick fix

> From: Jiri Kosina <jkosina@suse.cz>
> Subject: [PATCH] floppy: fix lock_fdc() signal handling
>
> floppy_revalidate() doesn't perform any error handling on lock_fdc()
> result. lock_fdc() might actually be interrupted by a signal (it waits for
> fdc becoming non-busy interruptibly). In such case, floppy_revalidate()
> proceeds as if it had claimed the lock, but it fact it doesn't.
>
> In case of multiple threads trying to open("/dev/fdX"), this leads to
> serious corruptions all over the place, because all of a sudden there is
> no critical section protection (that'd otherwise be guaranteed by locked
> fd) whatsoever.
>
> While at this, fix the fact that the 'interruptible' parameter to
> lock_fdc() doesn't make any sense whatsoever, because we always wait
> interruptibly anyway.
>
> Most of the lock_fdc() callsites do properly handle error (and propagate
> EINTR), but floppy_revalidate() and floppy_check_events() don't. Fix this.
>
> Spotted by 'syzkaller' tool.
>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Tested-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> ---
>  drivers/block/floppy.c | 33 ++++++++++++++++++---------------
>  1 file changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index 9e25120..b206115 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -866,7 +866,7 @@ static void set_fdc(int drive)
>  }
>
>  /* locks the driver */
> -static int lock_fdc(int drive, bool interruptible)
> +static int lock_fdc(int drive)
>  {
>         if (WARN(atomic_read(&usage_count) == 0,
>                  "Trying to lock fdc while usage count=0\n"))
> @@ -2173,7 +2173,7 @@ static int do_format(int drive, struct format_descr *tmp_format_req)
>  {
>         int ret;
>
> -       if (lock_fdc(drive, true))
> +       if (lock_fdc(drive))
>                 return -EINTR;
>
>         set_floppy(drive);
> @@ -2960,7 +2960,7 @@ static int user_reset_fdc(int drive, int arg, bool interruptible)
>  {
>         int ret;
>
> -       if (lock_fdc(drive, interruptible))
> +       if (lock_fdc(drive))
>                 return -EINTR;
>
>         if (arg == FD_RESET_ALWAYS)
> @@ -3243,7 +3243,7 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
>                 if (!capable(CAP_SYS_ADMIN))
>                         return -EPERM;
>                 mutex_lock(&open_lock);
> -               if (lock_fdc(drive, true)) {
> +               if (lock_fdc(drive)) {
>                         mutex_unlock(&open_lock);
>                         return -EINTR;
>                 }
> @@ -3263,7 +3263,7 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
>         } else {
>                 int oldStretch;
>
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 if (cmd != FDDEFPRM) {
>                         /* notice a disk change immediately, else
> @@ -3349,7 +3349,7 @@ static int get_floppy_geometry(int drive, int type, struct floppy_struct **g)
>         if (type)
>                 *g = &floppy_type[type];
>         else {
> -               if (lock_fdc(drive, false))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 if (poll_drive(false, 0) == -EINTR)
>                         return -EINTR;
> @@ -3433,7 +3433,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>                 if (UDRS->fd_ref != 1)
>                         /* somebody else has this drive open */
>                         return -EBUSY;
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>
>                 /* do the actual eject. Fails on
> @@ -3445,7 +3445,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>                 process_fd_request();
>                 return ret;
>         case FDCLRPRM:
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 current_type[drive] = NULL;
>                 floppy_sizes[drive] = MAX_DISK_SIZE << 1;
> @@ -3467,7 +3467,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>                 UDP->flags &= ~FTD_MSG;
>                 return 0;
>         case FDFMTBEG:
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 if (poll_drive(true, FD_RAW_NEED_DISK) == -EINTR)
>                         return -EINTR;
> @@ -3484,7 +3484,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>                 return do_format(drive, &inparam.f);
>         case FDFMTEND:
>         case FDFLUSH:
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 return invalidate_drive(bdev);
>         case FDSETEMSGTRESH:
> @@ -3507,7 +3507,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>                 outparam = UDP;
>                 break;
>         case FDPOLLDRVSTAT:
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 if (poll_drive(true, FD_RAW_NEED_DISK) == -EINTR)
>                         return -EINTR;
> @@ -3530,7 +3530,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>         case FDRAWCMD:
>                 if (type)
>                         return -EINVAL;
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 set_floppy(drive);
>                 i = raw_cmd_ioctl(cmd, (void __user *)param);
> @@ -3539,7 +3539,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
>                 process_fd_request();
>                 return i;
>         case FDTWADDLE:
> -               if (lock_fdc(drive, true))
> +               if (lock_fdc(drive))
>                         return -EINTR;
>                 twaddle();
>                 process_fd_request();
> @@ -3748,7 +3748,8 @@ static unsigned int floppy_check_events(struct gendisk *disk,
>                 return DISK_EVENT_MEDIA_CHANGE;
>
>         if (time_after(jiffies, UDRS->last_checked + UDP->checkfreq)) {
> -               lock_fdc(drive, false);
> +               if (lock_fdc(drive))
> +                       return -EINTR;
>                 poll_drive(false, 0);
>                 process_fd_request();
>         }
> @@ -3847,7 +3848,9 @@ static int floppy_revalidate(struct gendisk *disk)
>                          "VFS: revalidate called on non-open device.\n"))
>                         return -EFAULT;
>
> -               lock_fdc(drive, false);
> +               res = lock_fdc(drive);
> +               if (res)
> +                       return res;
>                 cf = (test_bit(FD_DISK_CHANGED_BIT, &UDRS->flags) ||
>                       test_bit(FD_VERIFY_BIT, &UDRS->flags));
>                 if (!(cf || test_bit(drive, &fake_change) || drive_no_geom(drive))) {