From: Yucong Sun Date: Fri, 25 Feb 2022 18:59:24 +0000 (-0800) Subject: bpf: Fix issue with bpf preload module taking over stdout/stdin of kernel. X-Git-Tag: v6.6.17~7931^2~185^2~17 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=80bebebdac935473568c27d4f1349dc8f9809bf7;p=platform%2Fkernel%2Flinux-rpi.git bpf: Fix issue with bpf preload module taking over stdout/stdin of kernel. In cb80ddc67152 ("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: cb80ddc67152 ("bpf: Convert bpf_preload.ko to use light skeleton.") Signed-off-by: Yucong Sun Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220225185923.2535519-1-fallentree@fb.com --- diff --git a/kernel/bpf/preload/bpf_preload_kern.c b/kernel/bpf/preload/bpf_preload_kern.c index 30207c048d36..5106b5372f0c 100644 --- a/kernel/bpf/preload/bpf_preload_kern.c +++ b/kernel/bpf/preload/bpf_preload_kern.c @@ -54,6 +54,13 @@ static int load_skel(void) err = PTR_ERR(progs_link); goto out; } + /* Avoid taking over stdin/stdout/stderr of init process. Zeroing out + * makes skel_closenz() a no-op later in iterators_bpf__destroy(). + */ + close_fd(skel->links.dump_bpf_map_fd); + skel->links.dump_bpf_map_fd = 0; + close_fd(skel->links.dump_bpf_prog_fd); + skel->links.dump_bpf_prog_fd = 0; return 0; out: free_links_and_skel();