Hi, Seth,
Seth Jenkins <sethjenkins@xxxxxxxxxx> writes:
> Commit e4a0d3e720e7 ("aio: Make it possible to remap aio ring") introduced
> a null-deref if mremap is called on an old aio mapping after fork as
> mm->ioctx_table will be set to NULL.
>
> Fixes: e4a0d3e720e7 ("aio: Make it possible to remap aio ring")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Seth Jenkins <sethjenkins@xxxxxxxxxx>
> ---
> fs/aio.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 5b2ff20ad322..74eae7de7323 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -361,16 +361,18 @@ static int aio_ring_mremap(struct vm_area_struct *vma)
> spin_lock(&mm->ioctx_lock);
> rcu_read_lock();
> table = rcu_dereference(mm->ioctx_table);
> - for (i = 0; i < table->nr; i++) {
> - struct kioctx *ctx;
> -
> - ctx = rcu_dereference(table->table[i]);
> - if (ctx && ctx->aio_ring_file == file) {
> - if (!atomic_read(&ctx->dead)) {
> - ctx->user_id = ctx->mmap_base = vma->vm_start;
> - res = 0;
> + if (table) {
> + for (i = 0; i < table->nr; i++) {
> + struct kioctx *ctx;
> +
> + ctx = rcu_dereference(table->table[i]);
> + if (ctx && ctx->aio_ring_file == file) {
> + if (!atomic_read(&ctx->dead)) {
> + ctx->user_id = ctx->mmap_base = vma->vm_start;
> + res = 0;
> + }
> + break;
> }
> - break;
> }
> }
I wonder if it would be better to not copy the ring mapping on fork.
Something like the below? I think that would be more in line with
expectations (the ring isn't available in the child process).
-Jeff
diff --git a/fs/aio.c b/fs/aio.c
index 562916d85cba..dbf3b0749cb4 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -390,7 +390,7 @@ static const struct vm_operations_struct aio_ring_vm_ops = {
static int aio_ring_mmap(struct file *file, struct vm_area_struct *vma)
{
- vma->vm_flags |= VM_DONTEXPAND;
+ vma->vm_flags |= VM_DONTEXPAND|VM_DONTCOPY;
vma->vm_ops = &aio_ring_vm_ops;
return 0;
}
