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80bebebdac
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
88 lines
1.9 KiB
C
88 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/init.h>
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#include <linux/module.h>
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#include "bpf_preload.h"
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#include "iterators/iterators.lskel.h"
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static struct bpf_link *maps_link, *progs_link;
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static struct iterators_bpf *skel;
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static void free_links_and_skel(void)
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{
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if (!IS_ERR_OR_NULL(maps_link))
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bpf_link_put(maps_link);
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if (!IS_ERR_OR_NULL(progs_link))
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bpf_link_put(progs_link);
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iterators_bpf__destroy(skel);
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}
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static int preload(struct bpf_preload_info *obj)
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{
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strlcpy(obj[0].link_name, "maps.debug", sizeof(obj[0].link_name));
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obj[0].link = maps_link;
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strlcpy(obj[1].link_name, "progs.debug", sizeof(obj[1].link_name));
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obj[1].link = progs_link;
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return 0;
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}
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static struct bpf_preload_ops ops = {
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.preload = preload,
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.owner = THIS_MODULE,
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};
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static int load_skel(void)
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{
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int err;
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skel = iterators_bpf__open();
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if (!skel)
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return -ENOMEM;
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err = iterators_bpf__load(skel);
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if (err)
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goto out;
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err = iterators_bpf__attach(skel);
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if (err)
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goto out;
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maps_link = bpf_link_get_from_fd(skel->links.dump_bpf_map_fd);
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if (IS_ERR(maps_link)) {
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err = PTR_ERR(maps_link);
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goto out;
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}
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progs_link = bpf_link_get_from_fd(skel->links.dump_bpf_prog_fd);
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if (IS_ERR(progs_link)) {
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err = PTR_ERR(progs_link);
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goto out;
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}
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/* Avoid taking over stdin/stdout/stderr of init process. Zeroing out
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* makes skel_closenz() a no-op later in iterators_bpf__destroy().
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*/
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close_fd(skel->links.dump_bpf_map_fd);
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skel->links.dump_bpf_map_fd = 0;
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close_fd(skel->links.dump_bpf_prog_fd);
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skel->links.dump_bpf_prog_fd = 0;
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return 0;
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out:
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free_links_and_skel();
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return err;
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}
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static int __init load(void)
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{
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int err;
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err = load_skel();
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if (err)
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return err;
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bpf_preload_ops = &ops;
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return err;
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}
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static void __exit fini(void)
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{
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bpf_preload_ops = NULL;
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free_links_and_skel();
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}
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late_initcall(load);
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module_exit(fini);
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MODULE_LICENSE("GPL");
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