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Incb80ddc671("bpf: Convert bpf_preload.ko to use light skeleton.") BPF preload was switched from user mode process to use in-kernel light skeleton instead. However, in the kernel context, early in the boot sequence, the first available FD can start from 0, instead of normally 3 for user mode process. So FDs 0 and 1 are then used for loaded BPF programs and prevent init process from setting up stdin/stdout/stderr on FD 0, 1, and 2 as expected. Before the fix: ls -lah /proc/1/fd/* lrwx------1 root root 64 Feb 23 17:20 /proc/1/fd/0 -> /dev/null lrwx------ 1 root root 64 Feb 23 17:20 /proc/1/fd/1 -> /dev/null lrwx------ 1 root root 64 Feb 23 17:20 /proc/1/fd/2 -> /dev/console lrwx------ 1 root root 64 Feb 23 17:20 /proc/1/fd/6 -> /dev/console lrwx------ 1 root root 64 Feb 23 17:20 /proc/1/fd/7 -> /dev/console After the fix: ls -lah /proc/1/fd/* lrwx------ 1 root root 64 Feb 24 21:23 /proc/1/fd/0 -> /dev/console lrwx------ 1 root root 64 Feb 24 21:23 /proc/1/fd/1 -> /dev/console lrwx------ 1 root root 64 Feb 24 21:23 /proc/1/fd/2 -> /dev/console Fix by closing prog FDs after initialization. struct bpf_prog's themselves are kept alive through direct kernel references taken with bpf_link_get_from_fd(). Fixes:cb80ddc671("bpf: Convert bpf_preload.ko to use light skeleton.") Signed-off-by: Yucong Sun <fallentree@fb.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220225185923.2535519-1-fallentree@fb.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.