[PATCH] net/mlx5e: Fix a race in command alloc flow

[Shifeng Li]

Fix a cmd->ent use after free due to a race on command entry.
Such race occurs when one of the commands releases its last refcount and
frees its index and entry while another process running command flush
flow takes refcount to this command entry. The process which handles
commands flush may see this command as needed to be flushed if the other
process allocated a ent->idx but didn't set ent to cmd->ent_arr in
cmd_work_handler(). Fix it by moving the assignment of cmd->ent_arr into
the spin lock.

[70013.081955] BUG: KASAN: use-after-free in mlx5_cmd_trigger_completions+0x1e2/0x4c0 [mlx5_core]
[70013.081967] Write of size 4 at addr ffff88880b1510b4 by task kworker/26:1/1433361
[70013.081968]
[70013.081989] CPU: 26 PID: 1433361 Comm: kworker/26:1 Kdump: loaded Tainted: G           OE     4.19.90-25.17.v2101.osc.sfc.6.10.0.0030.ky10.x86_64+debug #1
[70013.082001] Hardware name: SANGFOR 65N32-US/ASERVER-G-2605, BIOS SSSS5203 08/19/2020
[70013.082028] Workqueue: events aer_isr
[70013.082053] Call Trace:
[70013.082067]  dump_stack+0x8b/0xbb
[70013.082086]  print_address_description+0x6a/0x270
[70013.082102]  kasan_report+0x179/0x2c0
[70013.082133]  ? mlx5_cmd_trigger_completions+0x1e2/0x4c0 [mlx5_core]
[70013.082173]  mlx5_cmd_trigger_completions+0x1e2/0x4c0 [mlx5_core]
[70013.082213]  ? mlx5_cmd_use_polling+0x20/0x20 [mlx5_core]
[70013.082223]  ? kmem_cache_free+0x1ad/0x1e0
[70013.082267]  mlx5_cmd_flush+0x80/0x180 [mlx5_core]
[70013.082304]  mlx5_enter_error_state+0x106/0x1d0 [mlx5_core]
[70013.082338]  mlx5_try_fast_unload+0x2ea/0x4d0 [mlx5_core]
[70013.082377]  remove_one+0x200/0x2b0 [mlx5_core]
[70013.082390]  ? __pm_runtime_resume+0x58/0x70
[70013.082409]  pci_device_remove+0xf3/0x280
[70013.082426]  ? pcibios_free_irq+0x10/0x10
[70013.082439]  device_release_driver_internal+0x1c3/0x470
[70013.082453]  pci_stop_bus_device+0x109/0x160
[70013.082468]  pci_stop_and_remove_bus_device+0xe/0x20
[70013.082485]  pcie_do_fatal_recovery+0x167/0x550
[70013.082493]  aer_isr+0x7d2/0x960
[70013.082510]  ? aer_get_device_error_info+0x420/0x420
[70013.082526]  ? __schedule+0x821/0x2040
[70013.082536]  ? strscpy+0x85/0x180
[70013.082543]  process_one_work+0x65f/0x12d0
[70013.082556]  worker_thread+0x87/0xb50
[70013.082563]  ? __kthread_parkme+0x82/0xf0
[70013.082569]  ? process_one_work+0x12d0/0x12d0
[70013.082571]  kthread+0x2e9/0x3a0
[70013.082579]  ? kthread_create_worker_on_cpu+0xc0/0xc0
[70013.082592]  ret_from_fork+0x1f/0x40

Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Signed-off-by: Shifeng Li <lishifeng1992@xxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index d3ca745d107d..1f9c09065249 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
@@ -115,15 +115,18 @@ static u8 alloc_token(struct mlx5_cmd *cmd)
 	return token;
 }
 
-static int cmd_alloc_index(struct mlx5_cmd *cmd)
+static int cmd_alloc_index(struct mlx5_cmd *cmd, struct mlx5_cmd_work_ent *ent)
 {
 	unsigned long flags;
 	int ret;
 
 	spin_lock_irqsave(&cmd->alloc_lock, flags);
 	ret = find_first_bit(&cmd->bitmask, cmd->max_reg_cmds);
-	if (ret < cmd->max_reg_cmds)
+	if (ret < cmd->max_reg_cmds) {
 		clear_bit(ret, &cmd->bitmask);
+		ent->idx = ret;
+		cmd->ent_arr[ent->idx] = ent;
+	}
 	spin_unlock_irqrestore(&cmd->alloc_lock, flags);
 
 	return ret < cmd->max_reg_cmds ? ret : -ENOMEM;
@@ -957,7 +960,7 @@ static void cmd_work_handler(struct work_struct *work)
 	sem = ent->page_queue ? &cmd->pages_sem : &cmd->sem;
 	down(sem);
 	if (!ent->page_queue) {
-		alloc_ret = cmd_alloc_index(cmd);
+		alloc_ret = cmd_alloc_index(cmd, ent);
 		if (alloc_ret < 0) {
 			mlx5_core_err_rl(dev, "failed to allocate command entry\n");
 			if (ent->callback) {
@@ -972,15 +975,14 @@ static void cmd_work_handler(struct work_struct *work)
 			up(sem);
 			return;
 		}
-		ent->idx = alloc_ret;
 	} else {
 		ent->idx = cmd->max_reg_cmds;
 		spin_lock_irqsave(&cmd->alloc_lock, flags);
 		clear_bit(ent->idx, &cmd->bitmask);
+		cmd->ent_arr[ent->idx] = ent;
 		spin_unlock_irqrestore(&cmd->alloc_lock, flags);
 	}
 
-	cmd->ent_arr[ent->idx] = ent;
 	lay = get_inst(cmd, ent->idx);
 	ent->lay = lay;
 	memset(lay, 0, sizeof(*lay));
-- 
2.25.1