virtio/fs: Check capabilities & act accordingly #244
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When run in muvm as an unprivileged user, write operations right now kind of work by accident, since libkrun assumes it runs as root: - If the access is in root context, it assumes it does not need to change user. The access is then made as the user. - If the access is as the muvm user, it tries to change uid to that user, which succeeds as a no-op. The access is made as the user, and then it tries to change back to root after it, which spams an error message. - If the access is as any other user, it tries to change to that uid, which fails and the access fails. This behavior, except for the spammy error, is essentially what we want. Re-do the credential change logic to explicitly implement the above, without trying to change uid/gid at all if we do not have the capability. Signed-off-by: Asahi Lina <[email protected]>
This makes overlayfs mounts with virtiofs lower dirs work. Signed-off-by: Asahi Lina <[email protected]>
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Two changes that make the passthrough layer check whether it runs with the proper capabilities to do something (i.e. root) and, if not, make it not do it.
Needed for some experiments I'm trying with the FEX RootFS stuff, but also generally helpful (I don't expect anything else to be needed in libkrun, so I'm sending this early).