CVE-2026-80819
Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept
Published Sep 4, 2026
CVSS n/a
EPSS < 1%
KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept
rfcomm_sock_recvmsg() completes a deferred setup by calling
rfcomm_dlc_accept() without holding any RFCOMM lock:
if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d->flags)) {
rfcomm_dlc_accept(d);
return 0;
}
and rfcomm_dlc_accept() dereferences the session on its first line:
struct sock *sk = d->session->sock->sk;
Every other path that touches d->session runs under rfcomm_mutex:
rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(),
rfcomm_dlc_send_rpn(), and the RFCOMM thread through
rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as
"called under rfcomm_lock()". This call site is the only one that skips
it.
The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against
teardown, since __rfcomm_dlc_close() returns early when it wins the
test_and_clear. But rfcomm_recv_disc() forces the state first:
d->state = BT_CLOSED;
__rfcomm_dlc_close(d, err);
and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and
BT_CONNECT2. With the state already BT_CLOSED that switch does not
match, the bit is never consulted, and __rfcomm_dlc_close() falls
through to rfcomm_dlc_unlink(), which sets d->session = NULL.
So a remote DISC on a deferred dlc clears the session while leaving
RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the
test_and_clear and dereferences a NULL session. No timing window is
needed: once the DISC has been processed, the dereference is
unconditional.
Give rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and
rfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and
re-checks the session, around a __rfcomm_dlc_accept() that the two
in-core callers, which already hold the mutex, keep using.
Reproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated
over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the
RFCOMM PSM, starts a session, opens a dlc on a channel bound with
BT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on
the accepted socket then hits:
Oops: general protection fault
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
RIP: 0010:rfcomm_dlc_accept+0x54/0x350
Call Trace:
rfcomm_sock_recvmsg+0x1cd/0x230
sock_recvmsg+0x166/0x1c0
__sys_recvfrom+0x20d/0x300
0x10 is the offset of sock in struct rfcomm_session. With this patch the
same run completes with recv() returning 0 and no report, and lockdep
stays quiet, confirming rfcomm_mutex is still taken before lock_sock on
this path as it is on the thread side.
Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept
rfcomm_sock_recvmsg() completes a deferred setup by calling
rfcomm_dlc_accept() without holding any RFCOMM lock:
if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d->flags)) {
rfcomm_dlc_accept(d);
return 0;
}
and rfcomm_dlc_accept() dereferences the session on its first line:
struct sock *sk = d->session->sock->sk;
Every other path that touches d->session runs under rfcomm_mutex:
rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(),
rfcomm_dlc_send_rpn(), and the RFCOMM thread through
rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as
"called under rfcomm_lock()". This call site is the only one that skips
it.
The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against
teardown, since __rfcomm_dlc_close() returns early when it wins the
test_and_clear. But rfcomm_recv_disc() forces the state first:
d->state = BT_CLOSED;
__rfcomm_dlc_close(d, err);
and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and
BT_CONNECT2. With the state already BT_CLOSED that switch does not
match, the bit is never consulted, and __rfcomm_dlc_close() falls
through to rfcomm_dlc_unlink(), which sets d->session = NULL.
So a remote DISC on a deferred dlc clears the session while leaving
RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the
test_and_clear and dereferences a NULL session. No timing window is
needed: once the DISC has been processed, the dereference is
unconditional.
Give rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and
rfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and
re-checks the session, around a __rfcomm_dlc_accept() that the two
in-core callers, which already hold the mutex, keep using.
Reproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated
over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the
RFCOMM PSM, starts a session, opens a dlc on a channel bound with
BT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on
the accepted socket then hits:
Oops: general protection fault
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
RIP: 0010:rfcomm_dlc_accept+0x54/0x350
Call Trace:
rfcomm_sock_recvmsg+0x1cd/0x230
sock_recvmsg+0x166/0x1c0
__sys_recvfrom+0x20d/0x300
0x10 is the offset of sock in struct rfcomm_session. With this patch the
same run completes with recv() returning 0 and no report, and lockdep
stays quiet, confirming rfcomm_mutex is still taken before lock_sock on
this path as it is on the thread side.
Affected Products
-
CVE record
-
NVD configurations
No data
-
Red Hat packages
No data
-
OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
|
No data.
No data.
| Vendor | Product | Versions | ||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux Kernel |
|
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| Linux | Linux Kernel |
|
Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Debian DLA |
DLA-4777-1 | linux security update |
| Debian DLA |
DLA-4788-1 | linux-6.12 security update |
 Ubuntu USN |
USN-8961-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9019-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9020-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9022-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9023-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9024-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9025-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9026-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9029-1 | Linux kernel (Raspberry Pi) vulnerabilities |
| Ubuntu USN |
USN-9039-1 | Linux kernel (Azure CVM) vulnerabilities |
| Ubuntu USN |
USN-9040-1 | Linux kernel (Low Latency NVIDIA) vulnerabilities |
| Ubuntu USN |
USN-9066-1 | Linux kernel (HWE) vulnerabilities |
| Ubuntu USN |
USN-9091-1 | Linux kernel (NVIDIA Tegra) vulnerabilities |
Metrics
No CVSS v4.0
No CVSS v3.1
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.195% probability within 30 days)
Key SSVC decision points have not yet been added.
References
History
Sep 4, 2026 5:45 PM
Weaknesses updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-476 |
Sep 4, 2026 3:30 PM
Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept rfcomm_sock_recvmsg() completes a deferred setup by calling rfcomm_dlc_accept() without holding any RFCOMM lock: if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d->flags)) { rfcomm_dlc_accept(d); return 0; } and rfcomm_dlc_accept() dereferences the session on its first line: struct sock *sk = d->session->sock->sk; Every other path that touches d->session runs under rfcomm_mutex: rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(), rfcomm_dlc_send_rpn(), and the RFCOMM thread through rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as "called under rfcomm_lock()". This call site is the only one that skips it. The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against teardown, since __rfcomm_dlc_close() returns early when it wins the test_and_clear. But rfcomm_recv_disc() forces the state first: d->state = BT_CLOSED; __rfcomm_dlc_close(d, err); and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and BT_CONNECT2. With the state already BT_CLOSED that switch does not match, the bit is never consulted, and __rfcomm_dlc_close() falls through to rfcomm_dlc_unlink(), which sets d->session = NULL. So a remote DISC on a deferred dlc clears the session while leaving RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the test_and_clear and dereferences a NULL session. No timing window is needed: once the DISC has been processed, the dereference is unconditional. Give rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and rfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and re-checks the session, around a __rfcomm_dlc_accept() that the two in-core callers, which already hold the mutex, keep using. Reproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the RFCOMM PSM, starts a session, opens a dlc on a channel bound with BT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on the accepted socket then hits: Oops: general protection fault KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:rfcomm_dlc_accept+0x54/0x350 Call Trace: rfcomm_sock_recvmsg+0x1cd/0x230 sock_recvmsg+0x166/0x1c0 __sys_recvfrom+0x20d/0x300 0x10 is the offset of sock in struct rfcomm_session. With this patch the same run completes with recv() returning 0 and no report, and lockdep stays quiet, confirming rfcomm_mutex is still taken before lock_sock on this path as it is on the thread side. | |
| Title | Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Subscriptions
Weaknesses
