util/misc: support kernels where MFD_NOEXEC_SEAL does not enable sealing
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pobrn
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dvdhrm
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May 23, 2024
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(I can also amend the changes myself when applying the patch. Let me know!) |
…aling Newer Linux kernels do not unset `F_SEAL_SEAL` when `MFD_NOEXEC_SEAL` is supplied to `memfd_create()`[0]. Currently, `misc_memfd()` has a workaround for this peculiarity of the kernel, however, this workaround will break. Avoid the breakage by checking if the kernel added `F_SEAL_SEAL`, and only try to add it if it is not already present. Note that this kernel uAPI change does not affect dbus-broker's normal operations since it never attempts to create a memfd with `MFD_NOEXEC_SEAL` and without `MFD_ALLOW_SEALING`. Only the test suite would be broken on newer kernels without this change. [0]: https://lore.kernel.org/linux-mm/[email protected]/
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I have not seen the force-push, sorry for missing that. I adjusted the PR to keep the 80ch comment line limit and added minor memfd adjustments as add-on commits. The roll-up PR is pending as #371, so I am closing this one. Thanks a lot for pushing this forward! I still hope we can get the kernel side fixed. |
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I am trying to squash the kernel's peculiar behaviour of implicitly enabling sealing on
MFD_NOEXEC_SEAL.dbus-brokeris one of the affected programs, but as noted below, only the test suite would break, normal operations wouldn't. At least as far as I can tell.Newer Linux kernels do not unset
F_SEAL_SEALwhenMFD_NOEXEC_SEALis supplied tomemfd_create(). Currently,misc_memfd()has a workaround for this peculiarity of the kernel, however, this workaround will break.Avoid the breakage by checking if the kernel added
F_SEAL_SEAL, and only try to add it if it is not already present.Note that this kernel uAPI change does not affect dbus-broker's normal operations since it never attempts to create a memfd with
MFD_NOEXEC_SEALand withoutMFD_ALLOW_SEALING. Only the test suite would be broken on newer kernels without this change.v2: https://lore.kernel.org/linux-mm/[email protected]/
v1: https://lore.kernel.org/linux-mm/[email protected]/