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/20231112150030.84609-1-ryncsn@gmail.com/

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• 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