From: Steven Rostedt rostedt@goodmis.org

The timerlat tracer can use user space threads to check for osnoise and timer latency. If the program using this is killed via a SIGTERM, the threads are shutdown one at a time and another tracing instance can start up resetting the threads before they are fully closed. That causes the hrtimer assigned to the kthread to be shutdown and freed twice when the dying thread finally closes the file descriptors, causing a use-after-free bug.

Only cancel the hrtimer if the associated thread is still around. Also add the interface_lock around the resetting of the tlat_var->kthread.

Note, this is just a quick fix that can be backported to stable. A real fix is to have a better synchronization between the shutdown of old threads and the starting of new ones.

Link: https://lore.kernel.org/all/20240820130001.124768-1-tglozar@redhat.com/

Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: "Luis Claudio R. Goncalves" lgoncalv@redhat.com Link: https://lore.kernel.org/20240905085330.45985730@gandalf.local.home Fixes: e88ed227f639e ("tracing/timerlat: Add user-space interface") Reported-by: Tomas Glozar tglozar@redhat.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/trace_osnoise.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index d770927efcd9..48e5014dd4ab 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -252,6 +252,11 @@ static inline struct timerlat_variables *this_cpu_tmr_var(void) return this_cpu_ptr(&per_cpu_timerlat_var); }

+/* + * Protect the interface. + */ +static struct mutex interface_lock; + /* * tlat_var_reset - Reset the values of the given timerlat_variables */ @@ -259,14 +264,20 @@ static inline void tlat_var_reset(void) { struct timerlat_variables *tlat_var; int cpu; + + /* Synchronize with the timerlat interfaces */ + mutex_lock(&interface_lock); /* * So far, all the values are initialized as 0, so * zeroing the structure is perfect. */ for_each_cpu(cpu, cpu_online_mask) { tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu); + if (tlat_var->kthread) + hrtimer_cancel(&tlat_var->timer); memset(tlat_var, 0, sizeof(*tlat_var)); } + mutex_unlock(&interface_lock); } #else /* CONFIG_TIMERLAT_TRACER */ #define tlat_var_reset() do {} while (0) @@ -331,11 +342,6 @@ struct timerlat_sample { }; #endif

-/* - * Protect the interface. - */ -static struct mutex interface_lock; - /* * Tracer data. */ @@ -2591,7 +2597,8 @@ static int timerlat_fd_release(struct inode *inode, struct file *file) osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu); tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu);

- hrtimer_cancel(&tlat_var->timer); + if (tlat_var->kthread) + hrtimer_cancel(&tlat_var->timer); memset(tlat_var, 0, sizeof(*tlat_var));

osn_var->sampling = 0;