On Wed, 15 May 2024 23:11:12 -0700 Jeff Xu jeffxu@google.com wrote:
On Mon, May 13, 2024 at 12:15 PM Barnabás Pőcze pobrn@protonmail.com wrote:
`MFD_NOEXEC_SEAL` should remove the executable bits and set `F_SEAL_EXEC` to prevent further modifications to the executable bits as per the comment in the uapi header file:
not executable and sealed to prevent changing to executable
However, currently, it also unsets `F_SEAL_SEAL`, essentially acting as a superset of `MFD_ALLOW_SEALING`. Nothing implies that it should be so, and indeed up until the second version of the of the patchset[0] that introduced `MFD_EXEC` and `MFD_NOEXEC_SEAL`, `F_SEAL_SEAL` was not removed, however it was changed in the third revision of the patchset[1] without a clear explanation.
This behaviour is suprising for application developers, there is no documentation that would reveal that `MFD_NOEXEC_SEAL` has the additional effect of `MFD_ALLOW_SEALING`.
Ya, I agree that there should be documentation, such as a man page. I will work on that.
So do not remove `F_SEAL_SEAL` when `MFD_NOEXEC_SEAL` is requested. This is technically an ABI break, but it seems very unlikely that an application would depend on this behaviour (unless by accident).
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Reviewed-by: Jeff Xu jeffxu@google.com
It's a change to a userspace API, yes? Please let's have a detailed description of why this is OK. Why it won't affect any existing users.
Also, please let's give consideration to a -stable backport so that all kernel versions will eventually behave in the same manner.