Re: [PATCH v5 3/9] crash_dump: Disallow writing to dm-crypt configfs during kexec_file_load syscall

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

New issues:
- [High] Severe locking imbalance in `crash_load_dm_crypt_keys()` leads to a leaked mutex on the error path and unlocking an unacquired mutex on the success path.

Pre-existing issues:
- [High] Premature and unconditional reset of `is_dm_key_reused` to false breaks ARM64/LoongArch kexec load retries and defeats intended cleanup logic.
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commit a9405cf8948ba39213612c61a1f3b10b23f437e4
Author: Coiby Xu <coiby.xu@gmail.com>

crash_dump: Disallow writing to dm-crypt configfs during kexec_file_load syscall

This commit prevents concurrent writes to the configfs group during the
kexec_file_load syscall by utilizing config_keys_subsys.su_mutex. It aims to
avoid buffer overflows, stale keys, or memory leaks caused by changes to
dm-crypt keys during iteration.

> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> index 3a416933979f8..580534d43b66e 100644
> --- a/kernel/crash_dump_dm_crypt.c
> +++ b/kernel/crash_dump_dm_crypt.c

[ ... ]

> @@ -478,6 +490,9 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>  		"Loaded dm crypt keys to kexec_buffer bufsz=0x%lx memsz=0x%lx\n",
>  		kbuf.bufsz, kbuf.memsz);
>  
> +unlock:
> +	mutex_unlock(&config_keys_subsys.su_mutex);
> +

[Severity: High]
Looking at crash_load_dm_crypt_keys(), if kexec_add_buffer() fails earlier
in the function, it jumps to the out label, bypassing this unlock label.
Does this leak the config_keys_subsys.su_mutex if the lock was acquired?

Also, on the success path, mutex_unlock() is executed unconditionally. If
is_dm_key_reused was true at the top of the function, the mutex was never
acquired. Can this cause a kernel panic or corruption by unlocking an
unacquired mutex?

>  out:
> -	return r;
> +	is_dm_key_reused = false;
> +	return r;
>  }

[Severity: High]
This is a pre-existing issue, but since the error and success paths
unconditionally reset is_dm_key_reused to false here, does this break
architectures like ARM64 that might retry segment loading?

If load_other_segments() retries the load sequence, the second pass
through crash_load_dm_crypt_keys() will see is_dm_key_reused as false,
find zero keys, and silently load nothing into the kdump kernel.

Additionally, crash_dm_crypt_cleanup() checks !is_dm_key_reused to determine
whether it should free keys_header. Since the flag is unconditionally cleared
here first, does this defeat the intended cleanup protection logic?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260909003657.1570544-1-coiby.xu@gmail.com?part=3