On 3/21/23 1:44 PM, Savino Dicanosa wrote:
> When fixed files are unregistered, file_alloc_end and alloc_hint
> are not cleared. This can later cause a NULL pointer dereference in
> io_file_bitmap_get() if auto index selection is enabled via
> IORING_FILE_INDEX_ALLOC:
>
> [ 6.519129] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [...]
> [ 6.541468] RIP: 0010:_find_next_zero_bit+0x1a/0x70
> [...]
> [ 6.560906] Call Trace:
> [ 6.561322] <TASK>
> [ 6.561672] io_file_bitmap_get+0x38/0x60
> [ 6.562281] io_fixed_fd_install+0x63/0xb0
> [ 6.562851] ? __pfx_io_socket+0x10/0x10
> [ 6.563396] io_socket+0x93/0xf0
> [ 6.563855] ? __pfx_io_socket+0x10/0x10
> [ 6.564411] io_issue_sqe+0x5b/0x3d0
> [ 6.564914] io_submit_sqes+0x1de/0x650
> [ 6.565452] __do_sys_io_uring_enter+0x4fc/0xb20
> [ 6.566083] ? __do_sys_io_uring_register+0x11e/0xd80
> [ 6.566779] do_syscall_64+0x3c/0x90
> [ 6.567247] entry_SYSCALL_64_after_hwframe+0x72/0xdc
> [...]
>
> To fix the issue, set file alloc range and alloc_hint to zero after
> file tables are freed.
>
> Fixes: 4278a0deb1f6 ("io_uring: defer alloc_hint update to io_file_bitmap_set()")
> Signed-off-by: Savino Dicanosa <sd7.dev@xxxxx>
> ---
> io_uring/rsrc.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index e2bac9f89902..7a43aed8e395 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -794,6 +794,7 @@ void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
> }
> #endif
> io_free_file_tables(&ctx->file_table);
> + io_file_table_set_alloc_range(ctx, 0, 0);
> io_rsrc_data_free(ctx->file_data);
> ctx->file_data = NULL;
> ctx->nr_user_files = 0;
That looks good. Do you happen to have a test case as well? Would be nice
to add that to the liburing regression tests.
--
Jens Axboe
