CVE-2024-38588

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

ftrace: Fix possible use-after-free issue in ftrace_location()

KASAN reports a bug:

BUG: KASAN: use-after-free in ftrace_location+0x90/0x120 Read of size 8 at addr ffff888141d40010 by task insmod/424 CPU: 8 PID: 424 Comm: insmod Tainted: G W 6.9.0-rc2+ […] Call Trace: dump_stack_lvl+0x68/0xa0 print_report+0xcf/0x610 kasan_report+0xb5/0xe0 ftrace_location+0x90/0x120 register_kprobe+0x14b/0xa40 kprobe_init+0x2d/0xff0 [kprobe_example] do_one_initcall+0x8f/0x2d0 do_init_module+0x13a/0x3c0 load_module+0x3082/0x33d0 init_module_from_file+0xd2/0x130 __x64_sys_finit_module+0x306/0x440 do_syscall_64+0x68/0x140 entry_SYSCALL_64_after_hwframe+0x71/0x79

The root cause is that, in lookup_rec(), ftrace record of some address is being searched in ftrace pages of some module, but those ftrace pages at the same time is being freed in ftrace_release_mod() as the corresponding module is being deleted:

       CPU1                       |      CPU2

register_kprobes() { | delete_module() { check_kprobe_address_safe() { | arch_check_ftrace_location() { | ftrace_location() { | lookup_rec() // USE! | ftrace_release_mod() // Free!

To fix this issue:

1. Hold rcu lock as accessing ftrace pages in ftrace_location_range();
2. Use ftrace_location_range() instead of lookup_rec() in ftrace_location();
3. Call synchronize_rcu() before freeing any ftrace pages both in ftrace_process_locs()/ftrace_release_mod()/ftrace_free_mem().

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/1880a324af1c95940a7c954b6b937e86844a33bd
• https://git.kernel.org/stable/c/31310e373f4c8c74e029d4326b283e757edabc0b
• https://git.kernel.org/stable/c/66df065b3106964e667b37bf8f7e55ec69d0c1f6
• https://git.kernel.org/stable/c/7b4881da5b19f65709f5c18c1a4d8caa2e496461
• https://git.kernel.org/stable/c/8ea8ef5e42173560ac510e92a1cc797ffeea8831
• https://git.kernel.org/stable/c/dbff5f0bfb2416b8b55c105ddbcd4f885e98fada
• https://git.kernel.org/stable/c/e60b613df8b6253def41215402f72986fee3fc8d
• https://git.kernel.org/stable/c/eea46baf145150910ba134f75a67106ba2222c1b
• https://git.kernel.org/stable/c/31310e373f4c8c74e029d4326b283e757edabc0b
• https://git.kernel.org/stable/c/66df065b3106964e667b37bf8f7e55ec69d0c1f6
• https://git.kernel.org/stable/c/7b4881da5b19f65709f5c18c1a4d8caa2e496461
• https://git.kernel.org/stable/c/8ea8ef5e42173560ac510e92a1cc797ffeea8831
• https://git.kernel.org/stable/c/dbff5f0bfb2416b8b55c105ddbcd4f885e98fada
• https://git.kernel.org/stable/c/e60b613df8b6253def41215402f72986fee3fc8d