On 09/09/2020 00:43, Alexey Kardashevskiy wrote:
> init_srcu_struct_nodes() is called with is_static==true only internally
> and when this happens, the srcu->sda is not initialized in
> init_srcu_struct_fields() and we crash on dereferencing @sdp.
>
> This fixes the crash by moving "if (is_static)" out of the loop which
> only does useful work for is_static=false case anyway.
>
> Found by syzkaller.
>
> Signed-off-by: Alexey Kardashevskiy <[email protected]>
> ---
> kernel/rcu/srcutree.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index c100acf332ed..49b54a50bde8 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -135,6 +135,9 @@ static void init_srcu_struct_nodes(struct srcu_struct
> *ssp, bool is_static)
> levelspread[level - 1];
> }
>
> + if (is_static)
> + return;
Actually, this is needed here too:
if (!ssp->sda)
return;
as
ssp->sda = alloc_percpu(struct srcu_data)
can fail if the process is killed too soon - it is quite easy to get
this situation with syzkaller (syscalls fuzzer)
Makes sense?
> +
> /*
> * Initialize the per-CPU srcu_data array, which feeds into the
> * leaves of the srcu_node tree.
> @@ -161,8 +164,6 @@ static void init_srcu_struct_nodes(struct srcu_struct
> *ssp, bool is_static)
> timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
> sdp->ssp = ssp;
> sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
> - if (is_static)
> - continue;
>
> /* Dynamically allocated, better be no srcu_read_locks()! */
> for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
>
--
Alexey
