[PATCH v2 -next 0/2] security: Fix call security_backing_file_free second time

[Cai Xinchen <caixinchen1@huawei.com>]

v2: Move the call_void_hook(backing_file_free, ...) call in
security_backing_file_free() into the if-statment true block before we
set the backing file's LSM blob pointer to NULL and free the LSM blob.

I found the following path:

alloc_empty_backing-file
    init_file(&ff->file, xxx)
        -> file_ref_init(&f->f_ref, 1); // only 1
    error = init_backing_file
        -> security_backing_file_alloc
        -> rc = call_int_hook(backing_file_alloc, ...)
           if (unlikely(rc))
                security_backing_file_free(backing_file); // first call
    if (unlikely(error)) {
        fput(&ff->file);
         -> if (unlikely(file_ref_put(&file->f_ref))) // zero
                __fput_deferred(file);
                 -> ____fput -> __fput -> file_free(file);
                 -> backing_file_free(backing_file(f));
                 -> security_backing_file_free(&ff->file); // second call

Currently, only SELinux has the lsm backing_file_alloc hook, and it always
return 0. When security_backing_file_free is called for the first time,
the blobs pointer is set to NULL. Therefore, double free will not occur in
the code.

Cai Xinchen (2):
  security: Delete dumplicate assignment
  security: Fix call security_backing_file_free second time

 security/lsm_init.c | 1 -
 security/security.c | 3 +--
 2 files changed, 1 insertion(+), 3 deletions(-)

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2.34.1