Re: [PATCH bpf v5 1/2] bpf: fix unpopulated name_len field in perf_event link info

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... Fixes: 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event") Signed-off-by: tyrone-wu wudevelops@gmail.com Acked-by: Jiri Olsa jolsa@kernel.org

---

V4 -> V5: Link: https://lore.kernel.org/bpf/CALOAHbC5xm7Cbfhau3z5X2PqUhiHECNWAPtJCWiOVqTKmdZ...

• 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 {