From: Zheyu Ma <zheyuma97@gmail.com> [ Upstream commit 829933ef05a951c8ff140e814656d73e74915faf ] For each device, the nosy driver allocates a pcilynx structure. A use-after-free might happen in the following scenario: 1. Open nosy device for the first time and call ioctl with command NOSY_IOC_START, then a new client A will be malloced and added to doubly linked list. 2. Open nosy device for the second time and call ioctl with command NOSY_IOC_START, then a new client B will be malloced and added to doubly linked list. 3. Call ioctl with command NOSY_IOC_START for client A, then client A will be readded to the doubly linked list. Now the doubly linked list is messed up. 4. Close the first nosy device and nosy_release will be called. In nosy_release, client A will be unlinked and freed. 5. Close the second nosy device, and client A will be referenced, resulting in UAF. The root cause of this bug is that the element in the doubly linked list is reentered into the list. Fix this bug by adding a check before inserting a client. If a client is already in the linked list, don't insert it. The following KASAN report reveals it: BUG: KASAN: use-after-free in nosy_release+0x1ea/0x210 Write of size 8 at addr ffff888102ad7360 by task poc CPU: 3 PID: 337 Comm: poc Not tainted 5.12.0-rc5+ #6 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 Call Trace: nosy_release+0x1ea/0x210 __fput+0x1e2/0x840 task_work_run+0xe8/0x180 exit_to_user_mode_prepare+0x114/0x120 syscall_exit_to_user_mode+0x1d/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xae Allocated by task 337: nosy_open+0x154/0x4d0 misc_open+0x2ec/0x410 chrdev_open+0x20d/0x5a0 do_dentry_open+0x40f/0xe80 path_openat+0x1cf9/0x37b0 do_filp_open+0x16d/0x390 do_sys_openat2+0x11d/0x360 __x64_sys_open+0xfd/0x1a0 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xae Freed by task 337: kfree+0x8f/0x210 nosy_release+0x158/0x210 __fput+0x1e2/0x840 task_work_run+0xe8/0x180 exit_to_user_mode_prepare+0x114/0x120 syscall_exit_to_user_mode+0x1d/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xae The buggy address belongs to the object at ffff888102ad7300 which belongs to the cache kmalloc-128 of size 128 The buggy address is located 96 bytes inside of 128-byte region [ffff888102ad7300, ffff888102ad7380) [ Modified to use 'list_empty()' inside proper lock - Linus ] Link: https://lore.kernel.org/lkml/1617433116-5930-1-git-send-email-zheyuma97@gmai... Reported-and-tested-by: 马哲宇 (Zheyu Ma) <zheyuma97@gmail.com> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com> Cc: Greg Kroah-Hartman <greg@kroah.com> Cc: Stefan Richter <stefanr@s5r6.in-berlin.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> --- drivers/firewire/nosy.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/firewire/nosy.c b/drivers/firewire/nosy.c index a128dd1126ae4..ac85e03e88e16 100644 --- a/drivers/firewire/nosy.c +++ b/drivers/firewire/nosy.c @@ -359,6 +359,7 @@ nosy_ioctl(struct file *file, unsigned int cmd, unsigned long arg) struct client *client = file->private_data; spinlock_t *client_list_lock = &client->lynx->client_list_lock; struct nosy_stats stats; + int ret; switch (cmd) { case NOSY_IOC_GET_STATS: @@ -373,11 +374,15 @@ nosy_ioctl(struct file *file, unsigned int cmd, unsigned long arg) return 0; case NOSY_IOC_START: + ret = -EBUSY; spin_lock_irq(client_list_lock); - list_add_tail(&client->link, &client->lynx->client_list); + if (list_empty(&client->link)) { + list_add_tail(&client->link, &client->lynx->client_list); + ret = 0; + } spin_unlock_irq(client_list_lock); - return 0; + return ret; case NOSY_IOC_STOP: spin_lock_irq(client_list_lock); -- 2.25.1