[PATCH] Bluetooth: RFCOMM: Fix session UAF in set_termios

[PATCH] Bluetooth: RFCOMM: Fix session UAF in set_termios

[Chengfeng Ye]

rfcomm_tty_set_termios() tests dlc->session without rfcomm_mutex and
later passes the pointer to rfcomm_send_rpn(). The latter dereferences
both session->initiator and session->sock. Meanwhile, krfcommd can
unlink the DLC and free the session while holding rfcomm_mutex.

The race can proceed as follows:

  TTY ioctl task                 krfcommd
  --------------                 --------
  load dlc->session
  enter rfcomm_send_rpn()
                                 lock rfcomm_mutex
                                 clear dlc->session
                                 free session
                                 unlock rfcomm_mutex
  read session->initiator

KASAN reported:

  BUG: KASAN: slab-use-after-free in rfcomm_send_rpn+0x297/0x2a0
  Read of size 4 at addr ffff88810012a850 by task poc/92

  Call Trace:
   rfcomm_send_rpn+0x297/0x2a0
   rfcomm_tty_set_termios+0x50d/0x850
   tty_set_termios+0x596/0x950
   set_termios+0x46a/0x6e0
   tty_mode_ioctl+0x152/0xbd0
   tty_ioctl+0x915/0x1240
   __x64_sys_ioctl+0x134/0x1c0

  Allocated by task 92:
   rfcomm_session_add+0x9e/0x2e0
   rfcomm_dlc_open+0x8b1/0xe00
   rfcomm_dev_activate+0x85/0x1a0
   rfcomm_tty_open+0x90/0x280

  Freed by task 68:
   kfree+0x131/0x3c0
   rfcomm_session_del+0x119/0x180
   rfcomm_run+0x737/0x4710

Add rfcomm_dlc_send_rpn(), which holds rfcomm_mutex while it verifies
that the DLC is still attached and sends the RPN frame. Have the TTY
path use the helper and drop its unlocked session check. This keeps the
session valid through both the frame construction and socket send.

Fixes: 3a5e903c09ae ("[Bluetooth]: Implement RFCOMM remote port negotiation")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 include/net/bluetooth/rfcomm.h |  3 +++
 net/bluetooth/rfcomm/core.c    | 17 +++++++++++++++++
 net/bluetooth/rfcomm/tty.c     |  7 +++----
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/net/bluetooth/rfcomm.h b/include/net/bluetooth/rfcomm.h
index feb6b3ae5e69..102c278e3584 100644
--- a/include/net/bluetooth/rfcomm.h
+++ b/include/net/bluetooth/rfcomm.h
@@ -226,6 +226,9 @@ int rfcomm_send_rpn(struct rfcomm_session *s, int cr, u8 dlci,
 			u8 bit_rate, u8 data_bits, u8 stop_bits,
 			u8 parity, u8 flow_ctrl_settings,
 			u8 xon_char, u8 xoff_char, u16 param_mask);
+int rfcomm_dlc_send_rpn(struct rfcomm_dlc *d, u8 bit_rate, u8 data_bits,
+			u8 stop_bits, u8 parity, u8 flow_ctrl_settings,
+			u8 xon_char, u8 xoff_char, u16 param_mask);
 
 /* ---- RFCOMM DLCs (channels) ---- */
 struct rfcomm_dlc *rfcomm_dlc_alloc(gfp_t prio);
diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index ebeae17b71d1..75f7512dec54 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1028,6 +1028,23 @@ int rfcomm_send_rpn(struct rfcomm_session *s, int cr, u8 dlci,
 	return rfcomm_send_frame(s, buf, ptr - buf);
 }
 
+int rfcomm_dlc_send_rpn(struct rfcomm_dlc *d, u8 bit_rate, u8 data_bits,
+			u8 stop_bits, u8 parity, u8 flow_ctrl_settings,
+			u8 xon_char, u8 xoff_char, u16 param_mask)
+{
+	int err = -ENOTCONN;
+
+	rfcomm_lock();
+	if (d->session)
+		err = rfcomm_send_rpn(d->session, 1, d->dlci, bit_rate,
+				      data_bits, stop_bits, parity,
+				      flow_ctrl_settings, xon_char, xoff_char,
+				      param_mask);
+	rfcomm_unlock();
+
+	return err;
+}
+
 static int rfcomm_send_rls(struct rfcomm_session *s, int cr, u8 dlci, u8 status)
 {
 	struct rfcomm_hdr *hdr;
diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 4b9a699ec59b..b2c1060394e6 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -858,7 +858,7 @@ static void rfcomm_tty_set_termios(struct tty_struct *tty,
 
 	BT_DBG("tty %p termios %p", tty, old);
 
-	if (!dev || !dev->dlc || !dev->dlc->session)
+	if (!dev || !dev->dlc)
 		return;
 
 	/* Handle turning off CRTSCTS */
@@ -979,9 +979,8 @@ static void rfcomm_tty_set_termios(struct tty_struct *tty,
 	}
 
 	if (changes)
-		rfcomm_send_rpn(dev->dlc->session, 1, dev->dlc->dlci, baud,
-				data_bits, stop_bits, parity,
-				RFCOMM_RPN_FLOW_NONE, x_on, x_off, changes);
+		rfcomm_dlc_send_rpn(dev->dlc, baud, data_bits, stop_bits, parity,
+				    RFCOMM_RPN_FLOW_NONE, x_on, x_off, changes);
 }
 
 static void rfcomm_tty_throttle(struct tty_struct *tty)
-- 
2.43.0

RE: Bluetooth: RFCOMM: Fix session UAF in set_termios

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2389 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1130329

---Test result---

Test Summary:
CheckPatch                    PASS      0.89 seconds
VerifyFixes                   PASS      0.09 seconds
VerifySignedoff               PASS      0.09 seconds
GitLint                       PASS      0.23 seconds
SubjectPrefix                 PASS      0.09 seconds
BuildKernel                   PASS      20.00 seconds
CheckAllWarning               PASS      22.22 seconds
CheckSparse                   PASS      21.16 seconds
BuildKernel32                 PASS      19.44 seconds
CheckKernelLLVM               SKIP      0.00 seconds
TestRunnerSetup               PASS      361.91 seconds
TestRunner_l2cap-tester       PASS      47.05 seconds
TestRunner_iso-tester         PASS      65.58 seconds
TestRunner_bnep-tester        PASS      14.54 seconds
TestRunner_mgmt-tester        FAIL      171.52 seconds
TestRunner_rfcomm-tester      PASS      19.53 seconds
TestRunner_sco-tester         PASS      26.52 seconds
TestRunner_ioctl-tester       PASS      19.83 seconds
TestRunner_mesh-tester        FAIL      20.50 seconds
TestRunner_smp-tester         PASS      17.99 seconds
TestRunner_userchan-tester    PASS      15.91 seconds
TestRunner_6lowpan-tester     PASS      18.02 seconds
IncrementalBuild              PASS      19.23 seconds

Details
##############################
Test: CheckKernelLLVM - SKIP
Desc: Build kernel with LLVM + context analysis
Output:
Clang not found
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.182 seconds
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    1.981 seconds
Mesh - Send cancel - 2                               Timed out    1.993 seconds


https://github.com/bluez/bluetooth-next/pull/456

---
Regards,
Linux Bluetooth

Re: [PATCH] Bluetooth: RFCOMM: Fix session UAF in set_termios

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Mon, 20 Jul 2026 00:03:11 +0800 you wrote:
> rfcomm_tty_set_termios() tests dlc->session without rfcomm_mutex and
> later passes the pointer to rfcomm_send_rpn(). The latter dereferences
> both session->initiator and session->sock. Meanwhile, krfcommd can
> unlink the DLC and free the session while holding rfcomm_mutex.
> 
> The race can proceed as follows:
> 
> [...]

Here is the summary with links:
  - Bluetooth: RFCOMM: Fix session UAF in set_termios
    https://git.kernel.org/bluetooth/bluetooth-next/c/2ac5f666025e

You are awesome, thank you!
-- 
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