| Message ID | 20231212084444.4619b8ce@gandalf.local.home (mailing list archive) |
|---|---|
| State | Superseded |
| Commit | 3dff08c7e82fee7daa7028d82b3985061d0669f8 |
| Headers | show |
| Series | tracing: Add size check when printing trace_marker output | expand |
On 2023-12-12 08:44, Steven Rostedt wrote: > From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > If for some reason the trace_marker write does not have a nul byte for the > string, it will overflow the print: Does this result in leaking kernel memory to userspace ? If so, it should state "Fixes..." and CC stable. Thanks, Mathieu > > trace_seq_printf(s, ": %s", field->buf); > > The field->buf could be missing the nul byte. To prevent overflow, add the > max size that the buf can be by using the event size and the field > location. > > int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_seq_printf(s, ": %*s", max, field->buf); > > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> > --- > kernel/trace/trace_output.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c > index d8b302d01083..e11fb8996286 100644 > --- a/kernel/trace/trace_output.c > +++ b/kernel/trace/trace_output.c > @@ -1587,11 +1587,12 @@ static enum print_line_t trace_print_print(struct trace_iterator *iter, > { > struct print_entry *field; > struct trace_seq *s = &iter->seq; > + int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_assign_type(field, iter->ent); > > seq_print_ip_sym(s, field->ip, flags); > - trace_seq_printf(s, ": %s", field->buf); > + trace_seq_printf(s, ": %*s", max, field->buf); > > return trace_handle_return(s); > } > @@ -1600,10 +1601,11 @@ static enum print_line_t trace_print_raw(struct trace_iterator *iter, int flags, > struct trace_event *event) > { > struct print_entry *field; > + int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_assign_type(field, iter->ent); > > - trace_seq_printf(&iter->seq, "# %lx %s", field->ip, field->buf); > + trace_seq_printf(&iter->seq, "# %lx %*s", field->ip, max, field->buf); > > return trace_handle_return(&iter->seq); > }
On Tue, 12 Dec 2023 09:23:54 -0500 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > On 2023-12-12 08:44, Steven Rostedt wrote: > > From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > > > If for some reason the trace_marker write does not have a nul byte for the > > string, it will overflow the print: > > Does this result in leaking kernel memory to userspace ? If so, it > should state "Fixes..." and CC stable. No, it was triggered because of a bug elsewhere ;-) https://lore.kernel.org/linux-trace-kernel/20231212072558.61f76493@gandalf.local.home/ Which does have a Cc stable and Fixes tag. The event truncated the trace_marker output and caused the buffer overflow here. The trace_marker always adds a '\0', but that got dropped due to the other bug. This is just hardening the kernel. Note, this can only happen with the new code that allows trace_marker to use the max size of the buffer, which is for the next kernel release. -- Steve
On Tue, 12 Dec 2023 08:44:44 -0500 Steven Rostedt <rostedt@goodmis.org> wrote: > From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > If for some reason the trace_marker write does not have a nul byte for the > string, it will overflow the print: > > trace_seq_printf(s, ": %s", field->buf); > > The field->buf could be missing the nul byte. To prevent overflow, add the > max size that the buf can be by using the event size and the field > location. > > int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_seq_printf(s, ": %*s", max, field->buf); > This looks good to me. Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Thanks! > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> > --- > kernel/trace/trace_output.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c > index d8b302d01083..e11fb8996286 100644 > --- a/kernel/trace/trace_output.c > +++ b/kernel/trace/trace_output.c > @@ -1587,11 +1587,12 @@ static enum print_line_t trace_print_print(struct trace_iterator *iter, > { > struct print_entry *field; > struct trace_seq *s = &iter->seq; > + int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_assign_type(field, iter->ent); > > seq_print_ip_sym(s, field->ip, flags); > - trace_seq_printf(s, ": %s", field->buf); > + trace_seq_printf(s, ": %*s", max, field->buf); > > return trace_handle_return(s); > } > @@ -1600,10 +1601,11 @@ static enum print_line_t trace_print_raw(struct trace_iterator *iter, int flags, > struct trace_event *event) > { > struct print_entry *field; > + int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_assign_type(field, iter->ent); > > - trace_seq_printf(&iter->seq, "# %lx %s", field->ip, field->buf); > + trace_seq_printf(&iter->seq, "# %lx %*s", field->ip, max, field->buf); > > return trace_handle_return(&iter->seq); > } > -- > 2.42.0 >
On Tue, 12 Dec 2023 08:44:44 -0500 Steven Rostedt <rostedt@goodmis.org> wrote: > From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > If for some reason the trace_marker write does not have a nul byte for the > string, it will overflow the print: > > trace_seq_printf(s, ": %s", field->buf); > > The field->buf could be missing the nul byte. To prevent overflow, add the > max size that the buf can be by using the event size and the field > location. > > int max = iter->ent_size - offsetof(struct print_entry, buf); > > trace_seq_printf(s, ": %*s", max, field->buf); Bah, this needs to be: trace_seq_printf(s, ": %.*s", max, field->buf); Note the '.' between % and *. Otherwise it right aligns the output. This did fail the selftest for trace_printk(), but I modified the new one to add " *" to accommodate it :-p Sending out v2. -- Steve
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index d8b302d01083..e11fb8996286 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -1587,11 +1587,12 @@ static enum print_line_t trace_print_print(struct trace_iterator *iter, { struct print_entry *field; struct trace_seq *s = &iter->seq; + int max = iter->ent_size - offsetof(struct print_entry, buf); trace_assign_type(field, iter->ent); seq_print_ip_sym(s, field->ip, flags); - trace_seq_printf(s, ": %s", field->buf); + trace_seq_printf(s, ": %*s", max, field->buf); return trace_handle_return(s); } @@ -1600,10 +1601,11 @@ static enum print_line_t trace_print_raw(struct trace_iterator *iter, int flags, struct trace_event *event) { struct print_entry *field; + int max = iter->ent_size - offsetof(struct print_entry, buf); trace_assign_type(field, iter->ent); - trace_seq_printf(&iter->seq, "# %lx %s", field->ip, field->buf); + trace_seq_printf(&iter->seq, "# %lx %*s", field->ip, max, field->buf); return trace_handle_return(&iter->seq); }