* [PATCH] tracing: fprobe: fix the length of unused fgraph_data
@ 2026-03-23 10:19 Martin Kaiser
2026-03-23 12:06 ` Masami Hiramatsu
2026-03-23 14:48 ` Steven Rostedt
0 siblings, 2 replies; 6+ messages in thread
From: Martin Kaiser @ 2026-03-23 10:19 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu
Cc: Mathieu Desnoyers, linux-trace-kernel, linux-kernel,
Martin Kaiser, stable
If fprobe_entry does not fill the allocated fgraph_data completely, the
unused part is zeroed with memset.
Fix the length for this memset call. Both reserved_words and used are in
units of return stack words, but memset needs the number of bytes.
Cc: stable@vger.kernel.org
Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
---
kernel/trace/fprobe.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index dcadf1d23b8a..6a1192515afd 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
}
}
if (used < reserved_words)
- memset(fgraph_data + used, 0, reserved_words - used);
+ memset(fgraph_data + used, 0, (reserved_words - used) * sizeof(long));
/* If any exit_handler is set, data must be used. */
return used != 0;
--
2.43.7
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
2026-03-23 10:19 [PATCH] tracing: fprobe: fix the length of unused fgraph_data Martin Kaiser
@ 2026-03-23 12:06 ` Masami Hiramatsu
2026-03-23 14:48 ` Steven Rostedt
1 sibling, 0 replies; 6+ messages in thread
From: Masami Hiramatsu @ 2026-03-23 12:06 UTC (permalink / raw)
To: Martin Kaiser
Cc: Steven Rostedt, Mathieu Desnoyers, linux-trace-kernel,
linux-kernel, stable
On Mon, 23 Mar 2026 11:19:36 +0100
Martin Kaiser <martin@kaiser.cx> wrote:
> If fprobe_entry does not fill the allocated fgraph_data completely, the
> unused part is zeroed with memset.
>
> Fix the length for this memset call. Both reserved_words and used are in
> units of return stack words, but memset needs the number of bytes.
>
> Cc: stable@vger.kernel.org
> Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
> Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Good catch!
Thanks,
> ---
> kernel/trace/fprobe.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index dcadf1d23b8a..6a1192515afd 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
> }
> }
> if (used < reserved_words)
> - memset(fgraph_data + used, 0, reserved_words - used);
> + memset(fgraph_data + used, 0, (reserved_words - used) * sizeof(long));
>
> /* If any exit_handler is set, data must be used. */
> return used != 0;
> --
> 2.43.7
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
2026-03-23 10:19 [PATCH] tracing: fprobe: fix the length of unused fgraph_data Martin Kaiser
2026-03-23 12:06 ` Masami Hiramatsu
@ 2026-03-23 14:48 ` Steven Rostedt
2026-03-24 0:34 ` Masami Hiramatsu
1 sibling, 1 reply; 6+ messages in thread
From: Steven Rostedt @ 2026-03-23 14:48 UTC (permalink / raw)
To: Martin Kaiser
Cc: Masami Hiramatsu, Mathieu Desnoyers, linux-trace-kernel,
linux-kernel, stable
On Mon, 23 Mar 2026 11:19:36 +0100
Martin Kaiser <martin@kaiser.cx> wrote:
> If fprobe_entry does not fill the allocated fgraph_data completely, the
> unused part is zeroed with memset.
>
> Fix the length for this memset call. Both reserved_words and used are in
> units of return stack words, but memset needs the number of bytes.
>
> Cc: stable@vger.kernel.org
> Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
> Signed-off-by: Martin Kaiser <martin@kaiser.cx>
> ---
> kernel/trace/fprobe.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index dcadf1d23b8a..6a1192515afd 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
> }
> }
> if (used < reserved_words)
> - memset(fgraph_data + used, 0, reserved_words - used);
> + memset(fgraph_data + used, 0, (reserved_words - used) * sizeof(long));
So fgraph_data is only used internally between the fprobe_fgraph_entry()
and fprobe_return() as it only exists on the fgraph shadow stack. I'm not
even sure if the unused portion needs to be zeroed out.
Thus, this may be correct, but it doesn't look like a true bug that needs a
stable tag.
-- Steve
>
> /* If any exit_handler is set, data must be used. */
> return used != 0;
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
2026-03-23 14:48 ` Steven Rostedt
@ 2026-03-24 0:34 ` Masami Hiramatsu
2026-03-24 8:05 ` Martin Kaiser
0 siblings, 1 reply; 6+ messages in thread
From: Masami Hiramatsu @ 2026-03-24 0:34 UTC (permalink / raw)
To: Steven Rostedt
Cc: Martin Kaiser, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel, linux-kernel, stable
On Mon, 23 Mar 2026 10:48:18 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 23 Mar 2026 11:19:36 +0100
> Martin Kaiser <martin@kaiser.cx> wrote:
>
> > If fprobe_entry does not fill the allocated fgraph_data completely, the
> > unused part is zeroed with memset.
> >
> > Fix the length for this memset call. Both reserved_words and used are in
> > units of return stack words, but memset needs the number of bytes.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
> > Signed-off-by: Martin Kaiser <martin@kaiser.cx>
> > ---
> > kernel/trace/fprobe.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> > index dcadf1d23b8a..6a1192515afd 100644
> > --- a/kernel/trace/fprobe.c
> > +++ b/kernel/trace/fprobe.c
> > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
> > }
> > }
> > if (used < reserved_words)
> > - memset(fgraph_data + used, 0, reserved_words - used);
> > + memset(fgraph_data + used, 0, (reserved_words - used) * sizeof(long));
>
> So fgraph_data is only used internally between the fprobe_fgraph_entry()
> and fprobe_return() as it only exists on the fgraph shadow stack. I'm not
> even sure if the unused portion needs to be zeroed out.
>
> Thus, this may be correct, but it doesn't look like a true bug that needs a
> stable tag.
Hmm, indeed. Maybe we'd better just remove this memset from for-next.
Thanks,
>
> -- Steve
>
>
> >
> > /* If any exit_handler is set, data must be used. */
> > return used != 0;
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
2026-03-24 0:34 ` Masami Hiramatsu
@ 2026-03-24 8:05 ` Martin Kaiser
2026-03-24 15:39 ` Masami Hiramatsu
0 siblings, 1 reply; 6+ messages in thread
From: Martin Kaiser @ 2026-03-24 8:05 UTC (permalink / raw)
To: Masami Hiramatsu
Cc: Steven Rostedt, Mathieu Desnoyers, linux-trace-kernel,
linux-kernel, stable
Thus wrote Masami Hiramatsu (mhiramat@kernel.org):
> On Mon, 23 Mar 2026 10:48:18 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Mon, 23 Mar 2026 11:19:36 +0100
> > Martin Kaiser <martin@kaiser.cx> wrote:
> > > If fprobe_entry does not fill the allocated fgraph_data completely, the
> > > unused part is zeroed with memset.
> > > Fix the length for this memset call. Both reserved_words and used are in
> > > units of return stack words, but memset needs the number of bytes.
> > > Cc: stable@vger.kernel.org
> > > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
> > > Signed-off-by: Martin Kaiser <martin@kaiser.cx>
> > > ---
> > > kernel/trace/fprobe.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> > > index dcadf1d23b8a..6a1192515afd 100644
> > > --- a/kernel/trace/fprobe.c
> > > +++ b/kernel/trace/fprobe.c
> > > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
> > > }
> > > }
> > > if (used < reserved_words)
> > > - memset(fgraph_data + used, 0, reserved_words - used);
> > > + memset(fgraph_data + used, 0, (reserved_words - used) * sizeof(long));
> > So fgraph_data is only used internally between the fprobe_fgraph_entry()
> > and fprobe_return() as it only exists on the fgraph shadow stack. I'm not
> > even sure if the unused portion needs to be zeroed out.
> > Thus, this may be correct, but it doesn't look like a true bug that needs a
> > stable tag.
> Hmm, indeed. Maybe we'd better just remove this memset from for-next.
Ok, I see your point. I'll send a v2 that removes the memset.
Best regards,
Martin
> Thanks,
> > -- Steve
> > > /* If any exit_handler is set, data must be used. */
> > > return used != 0;
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
2026-03-24 8:05 ` Martin Kaiser
@ 2026-03-24 15:39 ` Masami Hiramatsu
0 siblings, 0 replies; 6+ messages in thread
From: Masami Hiramatsu @ 2026-03-24 15:39 UTC (permalink / raw)
To: Martin Kaiser
Cc: Steven Rostedt, Mathieu Desnoyers, linux-trace-kernel,
linux-kernel, stable
On Tue, 24 Mar 2026 09:05:12 +0100
Martin Kaiser <martin@kaiser.cx> wrote:
> Thus wrote Masami Hiramatsu (mhiramat@kernel.org):
>
> > On Mon, 23 Mar 2026 10:48:18 -0400
> > Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > > On Mon, 23 Mar 2026 11:19:36 +0100
> > > Martin Kaiser <martin@kaiser.cx> wrote:
>
> > > > If fprobe_entry does not fill the allocated fgraph_data completely, the
> > > > unused part is zeroed with memset.
>
> > > > Fix the length for this memset call. Both reserved_words and used are in
> > > > units of return stack words, but memset needs the number of bytes.
>
> > > > Cc: stable@vger.kernel.org
> > > > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
> > > > Signed-off-by: Martin Kaiser <martin@kaiser.cx>
> > > > ---
> > > > kernel/trace/fprobe.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
>
> > > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> > > > index dcadf1d23b8a..6a1192515afd 100644
> > > > --- a/kernel/trace/fprobe.c
> > > > +++ b/kernel/trace/fprobe.c
> > > > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
> > > > }
> > > > }
> > > > if (used < reserved_words)
> > > > - memset(fgraph_data + used, 0, reserved_words - used);
> > > > + memset(fgraph_data + used, 0, (reserved_words - used) * sizeof(long));
>
> > > So fgraph_data is only used internally between the fprobe_fgraph_entry()
> > > and fprobe_return() as it only exists on the fgraph shadow stack. I'm not
> > > even sure if the unused portion needs to be zeroed out.
>
> > > Thus, this may be correct, but it doesn't look like a true bug that needs a
> > > stable tag.
>
> > Hmm, indeed. Maybe we'd better just remove this memset from for-next.
>
> Ok, I see your point. I'll send a v2 that removes the memset.
Yeah, thanks!
>
> Best regards,
> Martin
>
> > Thanks,
>
>
> > > -- Steve
>
>
>
> > > > /* If any exit_handler is set, data must be used. */
> > > > return used != 0;
>
>
>
> > --
> > Masami Hiramatsu (Google) <mhiramat@kernel.org>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 6+ messages in thread
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2026-03-23 10:19 [PATCH] tracing: fprobe: fix the length of unused fgraph_data Martin Kaiser
2026-03-23 12:06 ` Masami Hiramatsu
2026-03-23 14:48 ` Steven Rostedt
2026-03-24 0:34 ` Masami Hiramatsu
2026-03-24 8:05 ` Martin Kaiser
2026-03-24 15:39 ` Masami Hiramatsu
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