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The kernel renders /proc/self/exe from the executable's file, whose mount belongs to the namespace the task started in. unshare(CLONE_NEWNS) moves the task's root and cwd to the corresponding mounts in the new copy, but not that file, so afterwards the path is walked up to the old namespace's root instead of the task's root. Normally they are the same directory, but when the task is chrooted (e.g. a container that entered its root with chroot rather than pivot_root) the old namespace's root is the host's, and the link reads as /path/to/container/root/bin/x rather than /bin/x. That path doesn't exist in the container, so the bind mount failed with ENOENT, with or without rr. Read the link before unsharing, when it is relative to the task's root, which is also valid in the new namespace. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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The kernel renders /proc/self/exe from the executable's file, whose mount belongs to the namespace the task started in. unshare(CLONE_NEWNS) moves the task's root and cwd to the corresponding mounts in the new copy, but not that file, so afterwards the path is walked up to the old namespace's root instead of the task's root. Normally they are the same directory, but when the task is chrooted (e.g. a container that entered its root with chroot rather than pivot_root) the old namespace's root is the host's, and the link reads as /path/to/container/root/bin/x rather than /bin/x. That path doesn't exist in the container, so the bind mount failed with ENOENT, with or without rr.
Read the link before unsharing, when it is relative to the task's root, which is also valid in the new namespace.