Re: [RESEND][PATCH] ima: Set and clear FMODE_CAN_READ in ima_calc_file_hash()

[Linus Torvalds]

On Mon, Nov 16, 2020 at 10:35 AM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote:
>
> We need to differentiate between signed files, which by definition are
> immutable, and those that are mutable.  Appending to a mutable file,
> for example, would result in the file hash not being updated.
> Subsequent reads would fail.

Why would that require any reading of the file at all AT WRITE TIME?

Don't do it. Really.

When opening the file write-only, you just invalidate the hash. It
doesn't matter anyway - you're only writing.

Later on, when reading, only at that point does the hash matter, and
then you can do the verification.

Although honestly, I don't even see the point. You know the hash won't
match, if you wrote to the file.

           Linus