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

From: tyrone-wu
Date: Sun Oct 06 2024 - 15:51:52 EST


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-yb0Snztmtg@xxxxxxxxxxxxxx/
Fixes: 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event")
Signed-off-by: tyrone-wu <wudevelops@xxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
V4 -> V5:
Link: https://lore.kernel.org/bpf/CALOAHbC5xm7Cbfhau3z5X2PqUhiHECNWAPtJCWiOVqTKmdZp-Q@xxxxxxxxxxxxxx/
- 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;
}
@@ -3609,7 +3612,7 @@ 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;
@@ -3617,7 +3620,7 @@ static int bpf_perf_link_fill_kprobe(const struct perf_event *event,
info->perf_event.type = BPF_PERF_EVENT_KRETPROBE;
else
info->perf_event.type = BPF_PERF_EVENT_KPROBE;
-
+ info->perf_event.kprobe.name_len = ulen;
info->perf_event.kprobe.offset = offset;
info->perf_event.kprobe.missed = missed;
if (!kallsyms_show_value(current_cred()))
@@ -3639,7 +3642,7 @@ static int bpf_perf_link_fill_uprobe(const struct perf_event *event,

uname = u64_to_user_ptr(info->perf_event.uprobe.file_name);
ulen = info->perf_event.uprobe.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, NULL);
if (err)
return err;
@@ -3648,6 +3651,7 @@ static int bpf_perf_link_fill_uprobe(const struct perf_event *event,
info->perf_event.type = BPF_PERF_EVENT_URETPROBE;
else
info->perf_event.type = BPF_PERF_EVENT_UPROBE;
+ info->perf_event.uprobe.name_len = ulen;
info->perf_event.uprobe.offset = offset;
info->perf_event.uprobe.cookie = event->bpf_cookie;
return 0;
@@ -3673,12 +3677,18 @@ static int bpf_perf_link_fill_tracepoint(const struct perf_event *event,
{
char __user *uname;
u32 ulen;
+ int err;

uname = u64_to_user_ptr(info->perf_event.tracepoint.tp_name);
ulen = info->perf_event.tracepoint.name_len;
+ err = bpf_perf_link_fill_common(event, uname, &ulen, NULL, NULL, NULL, NULL);
+ if (err)
+ return err;
+
info->perf_event.type = BPF_PERF_EVENT_TRACEPOINT;
+ info->perf_event.tracepoint.name_len = ulen;
info->perf_event.tracepoint.cookie = event->bpf_cookie;
- return bpf_perf_link_fill_common(event, uname, ulen, NULL, NULL, NULL, NULL);
+ return 0;
}

static int bpf_perf_link_fill_perf_event(const struct perf_event *event,
--
2.43.0