In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix use-after-free in print_graph_function_flags during tracer switching

Kairui reported a UAF issue in print_graph_function_flags() during
ftrace stress testing [1]. This issue can be reproduced if puting a
'mdelay(10)' after 'mutex_unlock(&trace_types_lock)' in s_start(),
and executing the following script:

  $ echo function_graph > current_tracer
  $ cat trace > /dev/null &
  $ sleep 5  # Ensure the 'cat' reaches the 'mdelay(10)' point
  $ echo timerlat > current_tracer

The root cause lies in the two calls to print_graph_function_flags
within print_trace_line during each s_show():

  * One through 'iter->trace->print_line()';
  * Another through 'event->funcs->trace()', which is hidden in
    print_trace_fmt() before print_trace_line returns.

Tracer switching only updates the former, while the latter continues
to use the print_line function of the old tracer, which in the script
above is print_graph_function_flags.

Moreover, when switching from the 'function_graph' tracer to the
'timerlat' tracer, s_start only calls graph_trace_close of the
'function_graph' tracer to free 'iter->private', but does not set
it to NULL. This provides an opportunity for 'event->funcs->trace()'
to use an invalid 'iter->private'.

To fix this issue, set 'iter->private' to NULL immediately after
freeing it in graph_trace_close(), ensuring that an invalid pointer
is not passed to other tracers. Additionally, clean up the unnecessary
'iter->private = NULL' during each 'cat trace' when using wakeup and
irqsoff tracers.

 [1] https://lore.kernel.org/all/[email protected]/

https://git.kernel.org/stable/c/099ef3385800828b74933a96c117574637c3fb3a

https://git.kernel.org/stable/c/42561fe62c3628ea3bc9623f64f047605e98857f

https://git.kernel.org/stable/c/70be951bc01e4a0e10d443f3510bb17426f257fb

https://git.kernel.org/stable/c/7f81f27b1093e4895e87b74143c59c055c3b1906

https://git.kernel.org/stable/c/81a85b12132c8ffe98f5ddbdc185481790aeaa1b

https://git.kernel.org/stable/c/a2cce54c1748216535dda02e185d07a084be837e

https://git.kernel.org/stable/c/c85efe6e13743cac6ba4ccf144cb91f44c86231a

https://git.kernel.org/stable/c/de7b309139f862a44379ecd96e93c9133c69f813

https://git.kernel.org/stable/c/f14752d66056d0c7bffe5092130409417d3baa70