Re: [PATCH] capability: WARN when invalid capability is requested rather than BUG/panic

[Bodo Eggert]

Eric Paris <eparis@xxxxxxxxxx> wrote:

> Do we have any concern of a module being compiled against a new kernel
> say with cap number 35 defined and then loaded into a kernel with only
> 34 capabilities?  Do we care about that forward compatibility?  If we
> care BUG is scary.  EPERM would be the right thing since clearly on this
> kernel the process can't possibly have cap #35.
> 
> We really have 4 options (in the order I like them).
> 
> 1) do nothing (garbage in garbage out, sometimes panic sometimes not)
> 2) mask CAP_TO_INDEX (garbage in garbage out, no panic)
> 3) BUG_ON(!cap_valid(flag)) (garbage in BUG out, no panic)
> 4) WARN_ON/EPERM (garbage in EPERM out, no panic)

5) Use a macro or inline function to test for $cap <= $max_cap, eliminating
   the test in the final code.

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