CVE-2025-22035

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]/

This vulnerability is rated as Moderate severity for Red Hat Enterprise Linux because triggering the flaw requires local administrative privileges to interact with kernel tracing controls. On typical installations, access to the tracefs interface is restricted to root or users possessing administrative capabilities like CAP_SYS_ADMIN. Because unprivileged accounts cannot initiate tracer switching or access restricted trace buffers, the impact is primarily confined to denial of service or instability induced by already privileged users.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.