Re: [PATCH 00/14] Make the user mode driver code a better citizen

Tetsuo Handa [off-list ref] writes:

On 2020/06/30 5:19, Eric W. Biederman wrote:

quoted

Tetsuo Handa [off-list ref] writes:

quoted

On 2020/06/29 4:44, Alexei Starovoitov wrote:

quoted

But all the defensive programming kinda goes against general kernel style.
I wouldn't do it. Especially pr_info() ?!
Though I don't feel strongly about it.

Honestly speaking, caller should check for errors and print appropriate
messages. info->wd.mnt->mnt_root != info->wd.dentry indicates that something
went wrong (maybe memory corruption). But other conditions are not fatal.
That is, I consider even pr_info() here should be unnecessary.

They were all should never happen cases.  Which is why my patches do:
if (WARN_ON_ONCE(...))

No. Fuzz testing (which uses panic_on_warn=1) will trivially hit them.
This bug was unfortunately not found by syzkaller because this path is
not easily reachable via syscall interface.

Absolutely yes.  These are cases that should never happen.
They should never be reachable by userspace.

It is absolutely a bug if these are hit by userspace.

Now if fuzzers want horrible cases to be even more horrible and change a
nice friendly warn into a panic that is their problem.  The issue being
do they capture the information the rest of us need to fix.

Eric