In the Linux kernel, the following vulnerability has been resolved:
padata: Fix refcnt handling in padata_free_shell()
In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead
to system UAF (Use-After-Free) issues. Due to the lengthy analysis of
the pcrypt_aead01 function call, I'll describe the problem scenario
using a simplified model:
Suppose there's a user of padata named user_function that adheres to
the padata requirement of calling padata_free_shell after serial()
has been invoked, as demonstrated in the following code:
struct request {
struct padata_priv padata;
struct completion *done;
};
void parallel(struct padata_priv *padata) {
do_something();
}
void serial(struct padata_priv *padata) {
struct request *request = container_of(padata,
struct request,
padata);
complete(request->done);
}
void user_function() {
DECLARE_COMPLETION(done)
padata->parallel = parallel;
padata->serial = serial;
padata_do_parallel();
wait_for_completion(&done);
padata_free_shell();
}In the corresponding padata.c file, there's the following code:
static void padata_serial_worker(struct work_struct *serial_work) {
...
cnt = 0;
while (!list_empty(&local_list)) {
...
padata->serial(padata);
cnt++;
}
local_bh_enable();
if (refcount_sub_and_test(cnt, &pd->refcnt))
padata_free_pd(pd);
}Because of the high system load and the accumulation of unexecuted
softirq at this moment, local_bh_enable() in padata takes longer
to execute than usual. Subsequently, when accessing pd->refcnt,
pd has already been released by padata_free_shell(), resulting
in a UAF issue with pd->refcnt.
The fix is straightforward: add refcount_dec_and_test before calling
padata_free_pd in padata_free_shell.
References
In the Linux kernel, the following vulnerability has been resolved:
padata: Fix refcnt handling in padata_free_shell()
In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead
to system UAF (Use-After-Free) issues. Due to the lengthy analysis of
the pcrypt_aead01 function call, I'll describe the problem scenario
using a simplified model:
Suppose there's a user of padata named
user_functionthat adheres tothe padata requirement of calling
padata_free_shellafterserial()has been invoked, as demonstrated in the following code:
In the corresponding padata.c file, there's the following code:
Because of the high system load and the accumulation of unexecuted
softirq at this moment,
local_bh_enable()in padata takes longerto execute than usual. Subsequently, when accessing
pd->refcnt,pdhas already been released bypadata_free_shell(), resultingin a UAF issue with
pd->refcnt.The fix is straightforward: add
refcount_dec_and_testbefore callingpadata_free_pdinpadata_free_shell.References