diff options
| author | Yucong Sun <fallentree@fb.com> | 2022-02-25 19:59:24 +0100 |
|---|---|---|
| committer | Andrii Nakryiko <andrii@kernel.org> | 2022-02-25 21:48:35 +0100 |
| commit | 80bebebdac935473568c27d4f1349dc8f9809bf7 (patch) | |
| tree | 4bdb1d6754c6afcf2d5fb6acc2bbe32af40ce802 /kernel/bpf/preload | |
| parent | bpftool: Bpf skeletons assert type sizes (diff) | |
| download | linux-80bebebdac935473568c27d4f1349dc8f9809bf7.tar.xz linux-80bebebdac935473568c27d4f1349dc8f9809bf7.zip | |
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 <fallentree@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220225185923.2535519-1-fallentree@fb.com
Diffstat (limited to 'kernel/bpf/preload')
| -rw-r--r-- | kernel/bpf/preload/bpf_preload_kern.c | 7 |
1 files changed, 7 insertions, 0 deletions
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(); |