Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-80819
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-04 16:18:09 UTC
Updated2026-09-04 16:18:09 UTC
DescriptionIn 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.

Risk And Classification

EPSS: 0.001950000 probability, percentile 0.092960000 (date 2026-09-06)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 d8d686dd5662a7c4745e4515f1237a9f3b7df181 git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2 git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 56f0aa75c7640e46397ef73bea251fcbef9150c0 git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 362726c9c6e56eea4262109183e49868c39ccd3a git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 825b95561d7b7c393df9e7bc295451aaeadc3d18 git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 d4b1a13b1eff2e80925c7368ffdeaaa50cba93df git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 355bfd57ca4ca881c6eb03ca813b440a094b1f44 git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 b405c2f96ae2e37375105881890f7738833b1d62 git Not specified
CNA Linux Linux affected bb23c0ab824653be4aa7dfca15b07b3059717004 43a556b2fd43f2df6dded59c2e26560a27874c24 git Not specified
CNA Linux Linux affected 2.6.30 Not specified
CNA Linux Linux unaffected 2.6.30 semver Not specified
CNA Linux Linux unaffected 5.10.267 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.218 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.185 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.154 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.106 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.47 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.11 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2.1 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/56f0aa75c7640e46397ef73bea251fcbef9150c0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/825b95561d7b7c393df9e7bc295451aaeadc3d18 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/43a556b2fd43f2df6dded59c2e26560a27874c24 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/362726c9c6e56eea4262109183e49868c39ccd3a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/355bfd57ca4ca881c6eb03ca813b440a094b1f44 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d4b1a13b1eff2e80925c7368ffdeaaa50cba93df 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d8d686dd5662a7c4745e4515f1237a9f3b7df181 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b405c2f96ae2e37375105881890f7738833b1d62 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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