Re: [PATCH bpf] bpf: fix unpopulated name_len field in perf_event link info

2024-10-02 Thread Jiri Olsa 
On Mon, Sep 30, 2024 at 11:59:20PM +, 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 
> ---
>  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

[PATCH bpf] bpf: fix unpopulated name_len field in perf_event link info

2024-09-30 Thread tyrone-wu 
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 
---
 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;
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;
@@ -3617,7 +3619,7 @@ 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 +3641,7 @@ 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 +3650,7 @@ 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 +3676,18 @@ 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,
diff --git a/tools/testing/selftests/bpf/prog_tests/fill_link_info.c 
b/tools/testing/selftests/bpf/prog_tests/fill_link_info.c
index f3932941bbaa..59077f260404 100644
--- a/tools/testing/