On Sun, Oct 06, 2024 at 07:51:30PM +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.
> 
> 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>
> Acked-by: Jiri Olsa <jo...@kernel.org>
> ---
> V4 -> V5:
> Link: 
> https://lore.kernel.org/bpf/caloahbc5xm7cbfhau3z5x2pquhihecnwaptjcwiovqtkmdz...@mail.gmail.com/
> - Check that buf is not NULL before retrieving/using its length
> 
> V3 -> V4:
> Link: https://lore.kernel.org/bpf/Zv_PP6Gs5cq3W2Ey@krava/
> - Split patch into separate kernel and selftest change
> 
> V2 -> V3:
> Link: https://lore.kernel.org/bpf/Zv7sISV0yEyGlEM3@krava/
> - Use clearer variable name for user set/inputted name len (name_len -> 
> input_len)
> - Change (name_len -> input_len) type from size_t to u32 since it's only 
> received and used as u32
> 
> V1 -> V2:
> Link: https://lore.kernel.org/bpf/Zv0wl-S13WJnIkb_@krava/
> - Use user set *ulen in bpf_copy_to_user before overwriting *ulen
> 
>  kernel/bpf/syscall.c | 38 ++++++++++++++++++++++++--------------
>  1 file changed, 24 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a8f1808a1ca5..3df192a6bdcc 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3565,32 +3565,35 @@ 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)
>  {
>       const char *buf;
> -     u32 prog_id;
> +     u32 prog_id, input_len;
>       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;
> -     if (!uname)
> -             return 0;
> +
>       if (buf) {
> +             input_len = *ulen;
>               len = strlen(buf);
> -             err = bpf_copy_to_user(uname, buf, ulen, len);
> -             if (err)
> -                     return err;
> -     } else {
> -             char zero = '\0';
> +             *ulen = len + 1;
>  
> +             if (uname) {
> +                     err = bpf_copy_to_user(uname, buf, input_len, len);
> +                     if (err)
> +                             return err;
> +             }
> +     } else if (uname) {
> +             char zero = '\0';
>               if (put_user(zero, uname))
>                       return -EFAULT;
>       }

hm, why not just simple check buf for and keep the rest? seems less 
complicated..

jirka


---
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a8f1808a1ca5..e393b94b90ec 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3565,27 +3565,31 @@ 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)
 {
        const char *buf;
-       u32 prog_id;
+       u32 prog_id, input_len;
        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;
+       if (buf) {
+               input_len = *ulen;
+               len = strlen(buf);
+               *ulen = len + 1;
+       }
        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, input_len, len);
                if (err)
                        return err;
        } else {

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