CVE-2026-80819 (GCVE-0-2026-80819)
Vulnerability from cvelistv5
Published
2026-09-04 15:13
Modified
2026-09-04 15:13
Severity ?
VLAI Severity ?
EPSS score ?
Summary
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.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 Version: bb23c0ab824653be4aa7dfca15b07b3059717004 |
||
{
"containers": {
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"programFiles": [
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{
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{
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{
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},
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},
{
"lessThanOrEqual": "*",
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"version": "7.3-rc1",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
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],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nBluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept\n\nrfcomm_sock_recvmsg() completes a deferred setup by calling\nrfcomm_dlc_accept() without holding any RFCOMM lock:\n\n\tif (test_and_clear_bit(RFCOMM_DEFER_SETUP, \u0026d-\u003eflags)) {\n\t\trfcomm_dlc_accept(d);\n\t\treturn 0;\n\t}\n\nand rfcomm_dlc_accept() dereferences the session on its first line:\n\n\tstruct sock *sk = d-\u003esession-\u003esock-\u003esk;\n\nEvery other path that touches d-\u003esession runs under rfcomm_mutex:\nrfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(),\nrfcomm_dlc_send_rpn(), and the RFCOMM thread through\nrfcomm_process_sessions(). rfcomm_connect_ind() is even documented as\n\"called under rfcomm_lock()\". This call site is the only one that skips\nit.\n\nThe RFCOMM_DEFER_SETUP bit looks like it serialises the accept against\nteardown, since __rfcomm_dlc_close() returns early when it wins the\ntest_and_clear. But rfcomm_recv_disc() forces the state first:\n\n\td-\u003estate = BT_CLOSED;\n\t__rfcomm_dlc_close(d, err);\n\nand the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and\nBT_CONNECT2. With the state already BT_CLOSED that switch does not\nmatch, the bit is never consulted, and __rfcomm_dlc_close() falls\nthrough to rfcomm_dlc_unlink(), which sets d-\u003esession = NULL.\n\nSo a remote DISC on a deferred dlc clears the session while leaving\nRFCOMM_DEFER_SETUP set. The next recvmsg() then passes the\ntest_and_clear and dereferences a NULL session. No timing window is\nneeded: once the DISC has been processed, the dereference is\nunconditional.\n\nGive rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and\nrfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and\nre-checks the session, around a __rfcomm_dlc_accept() that the two\nin-core callers, which already hold the mutex, keep using.\n\nReproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated\nover /dev/vhci: the peer brings up an ACL link, opens L2CAP on the\nRFCOMM PSM, starts a session, opens a dlc on a channel bound with\nBT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on\nthe accepted socket then hits:\n\n Oops: general protection fault\n KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]\n RIP: 0010:rfcomm_dlc_accept+0x54/0x350\n Call Trace:\n rfcomm_sock_recvmsg+0x1cd/0x230\n sock_recvmsg+0x166/0x1c0\n __sys_recvfrom+0x20d/0x300\n\n0x10 is the offset of sock in struct rfcomm_session. With this patch the\nsame run completes with recv() returning 0 and no report, and lockdep\nstays quiet, confirming rfcomm_mutex is still taken before lock_sock on\nthis path as it is on the thread side."
}
],
"providerMetadata": {
"dateUpdated": "2026-09-04T15:13:40.309Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/d8d686dd5662a7c4745e4515f1237a9f3b7df181"
},
{
"url": "https://git.kernel.org/stable/c/eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2"
},
{
"url": "https://git.kernel.org/stable/c/56f0aa75c7640e46397ef73bea251fcbef9150c0"
},
{
"url": "https://git.kernel.org/stable/c/362726c9c6e56eea4262109183e49868c39ccd3a"
},
{
"url": "https://git.kernel.org/stable/c/825b95561d7b7c393df9e7bc295451aaeadc3d18"
},
{
"url": "https://git.kernel.org/stable/c/d4b1a13b1eff2e80925c7368ffdeaaa50cba93df"
},
{
"url": "https://git.kernel.org/stable/c/355bfd57ca4ca881c6eb03ca813b440a094b1f44"
},
{
"url": "https://git.kernel.org/stable/c/b405c2f96ae2e37375105881890f7738833b1d62"
},
{
"url": "https://git.kernel.org/stable/c/43a556b2fd43f2df6dded59c2e26560a27874c24"
}
],
"title": "Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-80819",
"datePublished": "2026-09-04T15:13:40.309Z",
"dateReserved": "2026-08-26T14:34:25.795Z",
"dateUpdated": "2026-09-04T15:13:40.309Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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