From: Tony Ambardar tony.ambardar@gmail.com
commit e23bb04b0c938588eae41b7f4712b722290ed2b8 upstream.
If BTF data is missing or removed from the ELF section it is still exported via sysfs as a zero-length file:
root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux -r--r--r-- 1 root root 0 Jul 18 02:59 /sys/kernel/btf/vmlinux
Moreover, reads from this file succeed and leak kernel data:
root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10 000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................| 000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.| 000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................| 002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....| 002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|
This situation was first observed with kernel 5.4.x, cross-compiled for a MIPS target system. Fix by adding a sanity-check for export of zero-length data sections.
Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs") Signed-off-by: Tony Ambardar Tony.Ambardar@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: John Fastabend john.fastabend@gmail.com Acked-by: Andrii Nakryiko andriin@fb.com Link: https://lore.kernel.org/bpf/b38db205a66238f70823039a8c531535864eaac5.1600417... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/bpf/sysfs_btf.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/bpf/sysfs_btf.c +++ b/kernel/bpf/sysfs_btf.c @@ -30,15 +30,15 @@ static struct kobject *btf_kobj;
static int __init btf_vmlinux_init(void) { - if (!__start_BTF) + bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF; + + if (!__start_BTF || bin_attr_btf_vmlinux.size == 0) return 0;
btf_kobj = kobject_create_and_add("btf", kernel_kobj); if (!btf_kobj) return -ENOMEM;
- bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF; - return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux); }