linux-kernel - Unsafe find

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Message-ID: <ueprb5sfjisjucekft3ls7it3pacq44ryfyqtumb3be3itmzy4@mnp4e2lcbzus>
Date: Thu, 28 Nov 2024 15:58:06 +0100
From: Christian Brauner <brauner@...nel.org>
To: Scott Branden <scott.branden@...adcom.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Hans de Goede <hdegoede@...hat.com>, 
	Larry Finger <Larry.Finger@...inger.net>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	"Bcc:"@web.codeaurora.org
Subject: Unsafe find_vpid() calls

Hey,

You have various calls to find_vpid() in your drivers that aren't
protected by either tasklist_lock or rcu_read_lock(). Afair, this is
unsafe as the struct pid might be freed beneath you. You should please
fix those places to be protected by rcu_read_lock(). Something like the
below or similar should work.

Thanks!
Christian

diff --git a/drivers/misc/bcm-vk/bcm_vk_dev.c b/drivers/misc/bcm-vk/bcm_vk_dev.c
index d4a96137728d..84cab909db71 100644
--- a/drivers/misc/bcm-vk/bcm_vk_dev.c
+++ b/drivers/misc/bcm-vk/bcm_vk_dev.c
@@ -522,7 +522,9 @@ void bcm_vk_blk_drv_access(struct bcm_vk *vk)
                                dev_dbg(&vk->pdev->dev,
                                        "Send kill signal to pid %d\n",
                                        ctx->pid);
+                               rcu_read_lock();
                                kill_pid(find_vpid(ctx->pid), SIGKILL, 1);
+                               rcu_read_unlock();
                        }
                }
        }
diff --git a/drivers/misc/bcm-vk/bcm_vk_tty.c b/drivers/misc/bcm-vk/bcm_vk_tty.c
index 59bab76ff0a9..6bd93347938e 100644
--- a/drivers/misc/bcm-vk/bcm_vk_tty.c
+++ b/drivers/misc/bcm-vk/bcm_vk_tty.c
@@ -326,8 +326,11 @@ void bcm_vk_tty_terminate_tty_user(struct bcm_vk *vk)

        for (i = 0; i < BCM_VK_NUM_TTY; ++i) {
                vktty = &vk->tty[i];
-               if (vktty->pid)
+               if (vktty->pid) {
+                       rcu_read_lock();
                        kill_pid(find_vpid(vktty->pid), SIGKILL, 1);
+                       rcu_read_unlock();
+               }
        }
 }

diff --git a/drivers/staging/rtl8712/rtl8712_cmd.c b/drivers/staging/rtl8712/rtl8712_cmd.c
index bb7db96ed821..de13f4eab60f 100644
--- a/drivers/staging/rtl8712/rtl8712_cmd.c
+++ b/drivers/staging/rtl8712/rtl8712_cmd.c
@@ -61,7 +61,9 @@ static void check_hw_pbc(struct _adapter *padapter)
                 */
                if (padapter->pid == 0)
                        return;
+               rcu_read_lock();
                kill_pid(find_vpid(padapter->pid), SIGUSR1, 1);
+               rcu_read_unlock();
        }
 }