[PATCH bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry

[PATCH bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry

[Menglong Dong]

The error that returned by ftrace_set_filter_ip() in register_fentry() is
not handled properly. Just fix it.

Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
 kernel/bpf/trampoline.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 5949095e51c3..3610c6db15ee 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -220,7 +220,9 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 	}
 
 	if (tr->func.ftrace_managed) {
-		ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 1);
+		ret = ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 1);
+		if (ret)
+			return ret;
 		ret = register_ftrace_direct(tr->fops, (long)new_addr);
 	} else {
 		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
-- 
2.51.2

Re: [PATCH bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry

[Song Liu]

On Mon, Nov 10, 2025 at 4:07 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> The error that returned by ftrace_set_filter_ip() in register_fentry() is
> not handled properly. Just fix it.
>
> Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> ---
>  kernel/bpf/trampoline.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

LGTM. Thanks for the fix!

Acked-by: Song Liu <song@kernel.org>

Can we add a test for this code path?

Song

Re: [PATCH bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry

[Menglong Dong]

On 2025/11/10 23:49, Song Liu wrote:
> On Mon, Nov 10, 2025 at 4:07 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
> >
> > The error that returned by ftrace_set_filter_ip() in register_fentry() is
> > not handled properly. Just fix it.
> >
> > Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
> > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > ---
> >  kernel/bpf/trampoline.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> LGTM. Thanks for the fix!
> 
> Acked-by: Song Liu <song@kernel.org>
> 
> Can we add a test for this code path?

I think it can be done by attach a fentry to a notrace function and
check the error number.

Let me have a try.

> 
> Song
> 
> 

Re: [PATCH bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry

[Menglong Dong]

On 2025/11/11 08:59, Menglong Dong wrote:
> On 2025/11/10 23:49, Song Liu wrote:
> > On Mon, Nov 10, 2025 at 4:07 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > >
> > > The error that returned by ftrace_set_filter_ip() in register_fentry() is
> > > not handled properly. Just fix it.
> > >
> > > Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
> > > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > > ---
> > >  kernel/bpf/trampoline.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > LGTM. Thanks for the fix!
> > 
> > Acked-by: Song Liu <song@kernel.org>
> > 
> > Can we add a test for this code path?
> 
> I think it can be done by attach a fentry to a notrace function and
> check the error number.

Hmm...it's a little difficult to trigger this problem, as attaching a
notrace function won't go to this code patch ;|

> 
> Let me have a try.
> 
> > 
> > Song
> > 
> > 
> 
> 
> 
> 
> 
> 

Re: [PATCH bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Mon, 10 Nov 2025 20:07:05 +0800 you wrote:
> The error that returned by ftrace_set_filter_ip() in register_fentry() is
> not handled properly. Just fix it.
> 
> Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> ---
>  kernel/bpf/trampoline.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Here is the summary with links:
  - [bpf] bpf: handle the return of ftrace_set_filter_ip in register_fentry
    https://git.kernel.org/bpf/bpf-next/c/fea3f5e83c5c

You are awesome, thank you!
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