On Tue, Jan 22, 2019 at 05:13:35PM -0800, Andrey Smirnov wrote:
> On 32-bit systems, cheking for IS_ERR_VALUE(pos) is not
> correct. Expanding that code we get (loff_t cast is added for clarity):
>
> (loff_t)pos >= (unsigned long)-MAX_ERRNO
>
> given that loff_t is a 64-bit signed value, any perfectly valid seek
> offset that is greater than 0xffffc000 will result in false
> positive. Change the logic to check if position returned by
> fsdrv->lseek() is what's been requested. If it is, we can assume that
> operation was succesfull. If not, that's likely means failure and
> return value is a negative error code.
>
> This should accomodate both 32-bit systems, where we /dev/mem doesn't
> present any range problems, as well as 64-bit systems where both file
> offset and size of /dev/mem couldn't really be correctly captured by
> loff_t and we have to rely on 2's complement and overflow.
>
> Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
> ---
> fs/fs.c | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/fs/fs.c b/fs/fs.c
> index a304bf186..6a62fb98b 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -405,8 +405,7 @@ loff_t lseek(int fildes, loff_t offset, int whence)
> {
> struct fs_driver_d *fsdrv;
> FILE *f;
> - loff_t pos;
> - int ret;
> + loff_t pos, ret;
>
> if (check_fd(fildes))
> return -1;
> @@ -442,13 +441,11 @@ loff_t lseek(int fildes, loff_t offset, int whence)
> goto out;
> }
>
> - pos = fsdrv->lseek(&f->fsdev->dev, f, pos);
> - if (IS_ERR_VALUE(pos)) {
> - errno = -pos;
> - return -1;
> - }
> + ret = fsdrv->lseek(&f->fsdev->dev, f, pos);
> + if (ret != pos)
> + goto out;
There's no point in returning the current position from fsdrv->lseek
when the desired position is already an input parameter. I think we
should change the prototype of fsdrv->lseek to just return an error code.
Sascha
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