CVE-2022-50726 — net/mlx5: Fix possible use-after-free in async command interface

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: Fix possible use-after-free in async command interface

mlx5_cmd_cleanup_async_ctx should return only after all its callback handlers were completed. Before this patch, the below race between mlx5_cmd_cleanup_async_ctx and mlx5_cmd_exec_cb_handler was possible and lead to a use-after-free:

1. mlx5_cmd_cleanup_async_ctx is called while num_inflight is 2 (i.e. elevated by 1, a single inflight callback). 2. mlx5_cmd_cleanup_async_ctx decreases num_inflight to 1. 3. mlx5_cmd_exec_cb_handler is called, decreases num_inflight to 0 and is about to call wake_up(). 4. mlx5_cmd_cleanup_async_ctx calls wait_event, which returns immediately as the condition (num_inflight == 0) holds. 5. mlx5_cmd_cleanup_async_ctx returns. 6. The caller of mlx5_cmd_cleanup_async_ctx frees the mlx5_async_ctx object. 7. mlx5_cmd_exec_cb_handler goes on and calls wake_up() on the freed object.

Fix it by syncing using a completion object. Mark it completed when num_inflight reaches 0.

Trace:

BUG: KASAN: use-after-free in do_raw_spin_lock+0x23d/0x270 Read of size 4 at addr ffff888139cd12f4 by task swapper/5/0

CPU: 5 PID: 0 Comm: swapper/5 Not tainted 6.0.0-rc3_for_upstream_debug_2022_08_30_13_10 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 Call Trace: <IRQ> dump_stack_lvl+0x57/0x7d print_report.cold+0x2d5/0x684 ? do_raw_spin_lock+0x23d/0x…

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CVE-2022-50726 — net/mlx5: Fix possible use-after-free in async command interface