From: Lee Jones lee@kernel.org

[ Upstream commit 2d1e952a2b8e5e92d8d55ac88a7cf7ca5ea591ad ]

If a user can make copy_from_user() fail, there is a potential for UAF/DF due to a lack of locking around the allocation, use and freeing of the data buffers.

This issue is not theoretical. I managed to author a POC for it:

BUG: KASAN: double-free in kfree+0x5c/0xac Free of addr ffff29280be5de00 by task poc/356 CPU: 1 PID: 356 Comm: poc Not tainted 6.1.0-00001-g961aa6552c04-dirty #20 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace.part.0+0xe0/0xf0 show_stack+0x18/0x40 dump_stack_lvl+0x64/0x80 print_report+0x188/0x48c kasan_report_invalid_free+0xa0/0xc0 ____kasan_slab_free+0x174/0x1b0 __kasan_slab_free+0x18/0x24 __kmem_cache_free+0x130/0x2e0 kfree+0x5c/0xac mbox_test_message_write+0x208/0x29c full_proxy_write+0x90/0xf0 vfs_write+0x154/0x440 ksys_write+0xcc/0x180 __arm64_sys_write+0x44/0x60 invoke_syscall+0x60/0x190 el0_svc_common.constprop.0+0x7c/0x160 do_el0_svc+0x40/0xf0 el0_svc+0x2c/0x6c el0t_64_sync_handler+0xf4/0x120 el0t_64_sync+0x18c/0x190

Allocated by task 356: kasan_save_stack+0x3c/0x70 kasan_set_track+0x2c/0x40 kasan_save_alloc_info+0x24/0x34 __kasan_kmalloc+0xb8/0xc0 kmalloc_trace+0x58/0x70 mbox_test_message_write+0x6c/0x29c full_proxy_write+0x90/0xf0 vfs_write+0x154/0x440 ksys_write+0xcc/0x180 __arm64_sys_write+0x44/0x60 invoke_syscall+0x60/0x190 el0_svc_common.constprop.0+0x7c/0x160 do_el0_svc+0x40/0xf0 el0_svc+0x2c/0x6c el0t_64_sync_handler+0xf4/0x120 el0t_64_sync+0x18c/0x190

Freed by task 357: kasan_save_stack+0x3c/0x70 kasan_set_track+0x2c/0x40 kasan_save_free_info+0x38/0x5c ____kasan_slab_free+0x13c/0x1b0 __kasan_slab_free+0x18/0x24 __kmem_cache_free+0x130/0x2e0 kfree+0x5c/0xac mbox_test_message_write+0x208/0x29c full_proxy_write+0x90/0xf0 vfs_write+0x154/0x440 ksys_write+0xcc/0x180 __arm64_sys_write+0x44/0x60 invoke_syscall+0x60/0x190 el0_svc_common.constprop.0+0x7c/0x160 do_el0_svc+0x40/0xf0 el0_svc+0x2c/0x6c el0t_64_sync_handler+0xf4/0x120 el0t_64_sync+0x18c/0x190

Signed-off-by: Lee Jones lee@kernel.org Signed-off-by: Jassi Brar jaswinder.singh@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/mailbox/mailbox-test.c | 7 +++++++ 1 file changed, 7 insertions(+)

diff --git a/drivers/mailbox/mailbox-test.c b/drivers/mailbox/mailbox-test.c index 4555d678fadda..6dd5b9614452b 100644 --- a/drivers/mailbox/mailbox-test.c +++ b/drivers/mailbox/mailbox-test.c @@ -12,6 +12,7 @@ #include <linux/kernel.h> #include <linux/mailbox_client.h> #include <linux/module.h> +#include <linux/mutex.h> #include <linux/of.h> #include <linux/platform_device.h> #include <linux/poll.h> @@ -38,6 +39,7 @@ struct mbox_test_device { char *signal; char *message; spinlock_t lock; + struct mutex mutex; wait_queue_head_t waitq; struct fasync_struct *async_queue; struct dentry *root_debugfs_dir; @@ -110,6 +112,8 @@ static ssize_t mbox_test_message_write(struct file *filp, return -EINVAL; }

+ mutex_lock(&tdev->mutex); + tdev->message = kzalloc(MBOX_MAX_MSG_LEN, GFP_KERNEL); if (!tdev->message) return -ENOMEM; @@ -144,6 +148,8 @@ static ssize_t mbox_test_message_write(struct file *filp, kfree(tdev->message); tdev->signal = NULL;

+ mutex_unlock(&tdev->mutex); + return ret < 0 ? ret : count; }

@@ -392,6 +398,7 @@ static int mbox_test_probe(struct platform_device *pdev) platform_set_drvdata(pdev, tdev);

spin_lock_init(&tdev->lock); + mutex_init(&tdev->mutex);

if (tdev->rx_channel) { tdev->rx_buffer = devm_kzalloc(&pdev->dev,