I tried out the MAP_FIXED_NOREPLACE API introduced in Linux 4.17 for a minor use case in my hardened allocator and it turns out that it has been very broken since it was introduced. It can clobber adjacent mappings: https://marc.info/?l=linux-mm&m=153918527100638 … It will hopefully be fixed in 4.19.
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Replying to @DanielMicay
Even if fixed, it seems permanently unusable unless there's a way to ensure your kernel isn't affected.
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Replying to @RichFelker
It causes memory corruption so it's a security bug and could get a CVE assigned to encourage backporting for anyone using 4.17 and 4.18. It will hopefully be fixed before 4.19 is released. Bugs are usually a lot more subtle than this but that isn't necessarily a positive thing.
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Replying to @DanielMicay @RichFelker
it's fixed in Linus' tree now, with a stable backport marker: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7aa867dd89526e9cfd9714d8b9b587c016eaea34 …
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