Re: [PATCH] tracing: Fix trace_check_vprintf() when tp_printk is used

[Alison Schofield]

On Thu, Oct 03, 2024 at 10:49:25AM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
> 
> When the tp_printk kernel command line is used, the trace events go
> directly to printk(). It is still checked via the trace_check_vprintf()
> function to make sure the pointers of the trace event are legit.
> 
> The addition of reading buffers from previous boots required adding a
> delta between the addresses of the previous boot and the current boot so
> that the pointers in the old buffer can still be used. But this required
> adding a trace_array pointer to acquire the delta offsets.
> 
> The tp_printk code does not provide a trace_array (tr) pointer, so when
> the offsets were examined, a NULL pointer dereference happened and the
> kernel crashed.
> 
> If the trace_array does not exist, just default the delta offsets to zero,
> as that also means the trace event is not being read from a previous boot.
> 
> Link: https://lore.kernel.org/all/Zv3z5UsG_jsO9_Tb@xxxxxxxxxxxxxxxxxx/
> 

Thanks Steve!

Tested-by: Alison Schofield <alison.schofield@xxxxxxxxx>


> Reported-by: Alison Schofield <alison.schofield@xxxxxxxxx>
> Fixes: 07714b4bb3f98 ("tracing: Handle old buffer mappings for event strings and functions")
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
>  kernel/trace/trace.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
>
snip