Hi, On Sun, 7 Oct 2018 09:44:25 -0500 Wenwen Wang <wang6...@umn.edu> wrote:
> In vfio_spapr_iommu_eeh_ioctl(), if the ioctl command is VFIO_EEH_PE_OP, > the user-space buffer 'arg' is copied to the kernel object 'op' and the > 'argsz' and 'flags' fields of 'op' are checked. If the check fails, an > error code EINVAL is returned. Otherwise, 'op.op' is further checked > through a switch statement to invoke related handlers. If 'op.op' is > VFIO_EEH_PE_INJECT_ERR, the whole user-space buffer 'arg' is copied again > to 'op' to obtain the err information. However, in the following execution > of this case, the fields of 'op', except the field 'err', are actually not > used. That is, the second copy has a redundant part. Therefore, for both > performance and security reasons, the redundant part of the second copy > should be removed. Redundant, yes. Performance-wise it's 12 bytes on a non-performance path, so theoretically yes, but in practice maybe it's a simplicity trade-off. Security? I don't see it, please explain. > This patch removes such a part in the second copy. It only copies the 'err' > information from the buffer 'arg'. > > Signed-off-by: Wenwen Wang <wang6...@umn.edu> > --- > drivers/vfio/vfio_spapr_eeh.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/vfio/vfio_spapr_eeh.c b/drivers/vfio/vfio_spapr_eeh.c > index 38edeb4..5bc4b60 100644 > --- a/drivers/vfio/vfio_spapr_eeh.c > +++ b/drivers/vfio/vfio_spapr_eeh.c > @@ -86,10 +86,10 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group, > ret = eeh_pe_configure(pe); > break; > case VFIO_EEH_PE_INJECT_ERR: > - minsz = offsetofend(struct vfio_eeh_pe_op, err.mask); > - if (op.argsz < minsz) > + if (op.argsz < sizeof(op)) > return -EINVAL; The original code is written such that new operations can be added, possibly with new entries in the struct vfio_eeh_pe_op union, which might change sizeof(op) to be more than necessary for a VFIO_EEH_PE_INJECT_ERR op. Existing userspace suddenly wouldn't work without effectively reverting this change. This is a subtle dependency that is not worth the above code change, imo. > - if (copy_from_user(&op, (void __user *)arg, minsz)) > + if (copy_from_user(&op.err, (char __user *)arg + > + minsz, sizeof(op.err))) > return -EFAULT; Please rework with the assumption that the union in struct vfio_eeh_pe_op can be expanded and must not break existing userspace. Thanks, Alex
