nandfs: avoid integer overflow in nandfs_get_dat_bdescs_ioctl

[emaste]

Summary

nandfs removed from head in rS349352 but it's still in stable/12 and stable/11

Reported by: Ilja Van Sprundel <[e-mail]>

[imp]

These are fine but (a) you need to have mount privs to execute this ioctl; (b) nandfs is a panic trap due to bad locking and the system can't stay up once there's any vnode pressure at all; and (c) the set of nandfs users is the empty set due to (b). This is not exploitable in any meaningful way.

[emaste]

In D21232#461469, @imp wrote:

These are fine but (a) you need to have mount privs to execute this ioctl; (b) nandfs is a panic trap due to bad locking and the system can't stay up once there's any vnode pressure at all; and (c) the set of nandfs users is the empty set due to (b). This is not exploitable in any meaningful way.

and you have to go out of your way to build and run it. But the fix is easier than explaining that we don't care about nandfs.

[imp]

In D21232#461474, @emaste wrote:

In D21232#461469, @imp wrote:

These are fine but (a) you need to have mount privs to execute this ioctl; (b) nandfs is a panic trap due to bad locking and the system can't stay up once there's any vnode pressure at all; and (c) the set of nandfs users is the empty set due to (b). This is not exploitable in any meaningful way.

and you have to go out of your way to build and run it. But the fix is easier than explaining that we don't care about nandfs.

Yup. My feedback was to strongly bias against a SA for this :)