[PATCH 5.15] tty: n_gsm: Fix use-after-free in gsm_cleanup_mux

[PATCH 5.15] tty: n_gsm: Fix use-after-free in gsm_cleanup_mux

[mingli.yu]

From: Mingli Yu <mingli.yu@windriver.com>

commit 9462f4ca56e7d2430fdb6dcc8498244acbfc4489 upstream.

BUG: KASAN: slab-use-after-free in gsm_cleanup_mux+0x77b/0x7b0
drivers/tty/n_gsm.c:3160 [n_gsm]
Read of size 8 at addr ffff88815fe99c00 by task poc/3379
CPU: 0 UID: 0 PID: 3379 Comm: poc Not tainted 6.11.0+ #56
Hardware name: VMware, Inc. VMware Virtual Platform/440BX
Desktop Reference Platform, BIOS 6.00 11/12/2020
Call Trace:
 <TASK>
 gsm_cleanup_mux+0x77b/0x7b0 drivers/tty/n_gsm.c:3160 [n_gsm]
 __pfx_gsm_cleanup_mux+0x10/0x10 drivers/tty/n_gsm.c:3124 [n_gsm]
 __pfx_sched_clock_cpu+0x10/0x10 kernel/sched/clock.c:389
 update_load_avg+0x1c1/0x27b0 kernel/sched/fair.c:4500
 __pfx_min_vruntime_cb_rotate+0x10/0x10 kernel/sched/fair.c:846
 __rb_insert_augmented+0x492/0xbf0 lib/rbtree.c:161
 gsmld_ioctl+0x395/0x1450 drivers/tty/n_gsm.c:3408 [n_gsm]
 _raw_spin_lock_irqsave+0x92/0xf0 arch/x86/include/asm/atomic.h:107
 __pfx_gsmld_ioctl+0x10/0x10 drivers/tty/n_gsm.c:3822 [n_gsm]
 ktime_get+0x5e/0x140 kernel/time/timekeeping.c:195
 ldsem_down_read+0x94/0x4e0 arch/x86/include/asm/atomic64_64.h:79
 __pfx_ldsem_down_read+0x10/0x10 drivers/tty/tty_ldsem.c:338
 __pfx_do_vfs_ioctl+0x10/0x10 fs/ioctl.c:805
 tty_ioctl+0x643/0x1100 drivers/tty/tty_io.c:2818

Allocated by task 65:
 gsm_data_alloc.constprop.0+0x27/0x190 drivers/tty/n_gsm.c:926 [n_gsm]
 gsm_send+0x2c/0x580 drivers/tty/n_gsm.c:819 [n_gsm]
 gsm1_receive+0x547/0xad0 drivers/tty/n_gsm.c:3038 [n_gsm]
 gsmld_receive_buf+0x176/0x280 drivers/tty/n_gsm.c:3609 [n_gsm]
 tty_ldisc_receive_buf+0x101/0x1e0 drivers/tty/tty_buffer.c:391
 tty_port_default_receive_buf+0x61/0xa0 drivers/tty/tty_port.c:39
 flush_to_ldisc+0x1b0/0x750 drivers/tty/tty_buffer.c:445
 process_scheduled_works+0x2b0/0x10d0 kernel/workqueue.c:3229
 worker_thread+0x3dc/0x950 kernel/workqueue.c:3391
 kthread+0x2a3/0x370 kernel/kthread.c:389
 ret_from_fork+0x2d/0x70 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:257

Freed by task 3367:
 kfree+0x126/0x420 mm/slub.c:4580
 gsm_cleanup_mux+0x36c/0x7b0 drivers/tty/n_gsm.c:3160 [n_gsm]
 gsmld_ioctl+0x395/0x1450 drivers/tty/n_gsm.c:3408 [n_gsm]
 tty_ioctl+0x643/0x1100 drivers/tty/tty_io.c:2818

[Analysis]
gsm_msg on the tx_ctrl_list or tx_data_list of gsm_mux
can be freed by multi threads through ioctl,which leads
to the occurrence of uaf. Protect it by gsm tx lock.

Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
Cc: stable <stable@kernel.org>
Suggested-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20240926130213.531959-1-xialonglong@kylinos.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Mingli: Backport to fix CVE-2024-50073, no guard macro defined resolution]
Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
---
 drivers/tty/n_gsm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index aae9f73585bd..1becbdf7c470 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2443,6 +2443,7 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
 	int i;
 	struct gsm_dlci *dlci;
 	struct gsm_msg *txq, *ntxq;
+	unsigned long flags;
 
 	gsm->dead = true;
 	mutex_lock(&gsm->mutex);
@@ -2471,9 +2472,12 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
 	mutex_unlock(&gsm->mutex);
 	/* Now wipe the queues */
 	tty_ldisc_flush(gsm->tty);
+
+	spin_lock_irqsave(&gsm->tx_lock, flags);
 	list_for_each_entry_safe(txq, ntxq, &gsm->tx_list, list)
 		kfree(txq);
 	INIT_LIST_HEAD(&gsm->tx_list);
+	spin_unlock_irqrestore(&gsm->tx_lock, flags);
 }
 
 /**
-- 
2.34.1

Re: [PATCH 5.15] tty: n_gsm: Fix use-after-free in gsm_cleanup_mux

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 9462f4ca56e7d2430fdb6dcc8498244acbfc4489

WARNING: Author mismatch between patch and upstream commit:
Backport author: <mingli.yu@eng.windriver.com>
Commit author: Longlong Xia <xialonglong@kylinos.cn>


Status in newer kernel trees:
6.12.y | Present (exact SHA1)
6.11.y | Present (different SHA1: 0eec592c6a74)
6.6.y | Present (different SHA1: c29f192e0d44)
6.1.y | Present (different SHA1: bf171b5e86e4)
5.15.y | Not found

Note: The patch differs from the upstream commit:
---
--- -	2024-11-28 06:08:35.250028823 -0500
+++ /tmp/tmp.0bKgeyF8zy	2024-11-28 06:08:35.245548384 -0500
@@ -1,3 +1,5 @@
+commit 9462f4ca56e7d2430fdb6dcc8498244acbfc4489 upstream.
+
 BUG: KASAN: slab-use-after-free in gsm_cleanup_mux+0x77b/0x7b0
 drivers/tty/n_gsm.c:3160 [n_gsm]
 Read of size 8 at addr ffff88815fe99c00 by task poc/3379
@@ -51,20 +53,37 @@
 Suggested-by: Jiri Slaby <jirislaby@kernel.org>
 Link: https://lore.kernel.org/r/20240926130213.531959-1-xialonglong@kylinos.cn
 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+[Mingli: Backport to fix CVE-2024-50073, no guard macro defined resolution]
+Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
 ---
- drivers/tty/n_gsm.c | 2 ++
- 1 file changed, 2 insertions(+)
+ drivers/tty/n_gsm.c | 4 ++++
+ 1 file changed, 4 insertions(+)
 
 diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
-index 5d37a09849163..252849910588f 100644
+index aae9f73585bd..1becbdf7c470 100644
 --- a/drivers/tty/n_gsm.c
 +++ b/drivers/tty/n_gsm.c
-@@ -3157,6 +3157,8 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
+@@ -2443,6 +2443,7 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
+ 	int i;
+ 	struct gsm_dlci *dlci;
+ 	struct gsm_msg *txq, *ntxq;
++	unsigned long flags;
+ 
+ 	gsm->dead = true;
+ 	mutex_lock(&gsm->mutex);
+@@ -2471,9 +2472,12 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
  	mutex_unlock(&gsm->mutex);
  	/* Now wipe the queues */
  	tty_ldisc_flush(gsm->tty);
 +
-+	guard(spinlock_irqsave)(&gsm->tx_lock);
- 	list_for_each_entry_safe(txq, ntxq, &gsm->tx_ctrl_list, list)
++	spin_lock_irqsave(&gsm->tx_lock, flags);
+ 	list_for_each_entry_safe(txq, ntxq, &gsm->tx_list, list)
  		kfree(txq);
- 	INIT_LIST_HEAD(&gsm->tx_ctrl_list);
+ 	INIT_LIST_HEAD(&gsm->tx_list);
++	spin_unlock_irqrestore(&gsm->tx_lock, flags);
+ }
+ 
+ /**
+-- 
+2.34.1
+
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.15.y       |  Success    |  Success   |