On Mon, Sep 30, 2024 at 11:59:20PM +0000, tyrone-wu wrote:
> Previously when retrieving `bpf_link_info.perf_event` for
> kprobe/uprobe/tracepoint, the `name_len` field was not populated by the
> kernel, leaving it to reflect the value initially set by the user. This
> behavior was inconsistent with how other input/output string buffer
> fields function (e.g. `raw_tracepoint.tp_name_len`).
>
> This patch fills `name_len` with the actual size of the string name. The
> relevant selftests have also been updated to assert that `name_len`
> contains the correct size rather than 0.
>
> Link:
> https://lore.kernel.org/bpf/cabvu1kxwqxhqqge0rtrr7eegtm6svw_kayzby16-yb0snzt...@mail.gmail.com/
> Fixes: 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event")
> Signed-off-by: tyrone-wu <wudevel...@gmail.com>
> ---
> kernel/bpf/syscall.c | 25 +++++++++++++------
> .../selftests/bpf/prog_tests/fill_link_info.c | 6 ++---
> 2 files changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a8f1808a1ca5..90b6add4d0c9 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3565,7 +3565,7 @@ static void bpf_perf_link_dealloc(struct bpf_link *link)
> }
>
> static int bpf_perf_link_fill_common(const struct perf_event *event,
> - char __user *uname, u32 ulen,
> + char __user *uname, u32 *ulen,
> u64 *probe_offset, u64 *probe_addr,
> u32 *fd_type, unsigned long *missed)
> {
> @@ -3574,18 +3574,20 @@ static int bpf_perf_link_fill_common(const struct
> perf_event *event,
> size_t len;
> int err;
>
> - if (!ulen ^ !uname)
> + if (!(*ulen) ^ !uname)
> return -EINVAL;
>
> err = bpf_get_perf_event_info(event, &prog_id, fd_type, &buf,
> probe_offset, probe_addr, missed);
> if (err)
> return err;
> +
> + len = strlen(buf);
> + *ulen = len + 1;
I think before you overwrite *ulen with actual name lenth you should
store its value and use it in bpf_copy_to_user, otherwise we could
overwrite user space memory that we are not supposed to
jirka
> if (!uname)
> return 0;
> if (buf) {
> - len = strlen(buf);
> - err = bpf_copy_to_user(uname, buf, ulen, len);
> + err = bpf_copy_to_user(uname, buf, *ulen, len);
> if (err)
> return err;
> } else {
> @@ -3609,7 +3611,7 @@ static int bpf_perf_link_fill_kprobe(const struct
> perf_event *event,
>
> uname = u64_to_user_ptr(info->perf_event.kprobe.func_name);
> ulen = info->perf_event.kprobe.name_len;
> - err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
> + err = bpf_perf_link_fill_common(event, uname, &ulen, &offset, &addr,
> &type, &missed);
> if (err)
> return err;
SNIP
