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[release/2.1] Fix alternate stack for Alpine docker on SELinux (#17936) #17975
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For some reason, the Alpine docker container running on a SELinux host maps heap as RWX. When we allocate alternate stack from the heap, we also change the protection of the first page to PROT_NONE so that it can serve as a guard page to catch stack overflow. And when we free the alternate stack, we restore the protection back to PROT_READ | PROT_WRITE. The restoration fails in Alpine docker container running on a SELinux host with EPROT failure and the SELinux log reports that an attempt to change heap to executable was made. So it looks like the kernel has added the PERM_EXEC to the permissions we have passed to the mprotect call. There is a code in the mprotect implementation that can do that, although I don't fully understand the conditions under which it happens. This is driven by the VM_MAYEXEC flag in the internal VMA block structure. To fix that, I've modified the alternate stack allocation to use mmap / munmap instead of C heap allocation.
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@danmosemsft @Petermarcu said we will not put it to the 2.1 release and it will go to the first servicing release for 2.1. The reason is that it is too late and there is not enough time left to make the change bake itself for sufficient amount of time. |
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Port of #17936
Fixes #17931
@janvorli @RussKeldorph