GHSA-JHJ6-5P6X-HW75
Vulnerability from github – Published: 2026-05-01 15:30 – Updated: 2026-05-07 18:30In the Linux kernel, the following vulnerability has been resolved:
atm: lec: fix use-after-free in sock_def_readable()
A race condition exists between lec_atm_close() setting priv->lecd to NULL and concurrent access to priv->lecd in send_to_lecd(), lec_handle_bridge(), and lec_atm_send(). When the socket is freed via RCU while another thread is still using it, a use-after-free occurs in sock_def_readable() when accessing the socket's wait queue.
The root cause is that lec_atm_close() clears priv->lecd without any synchronization, while callers dereference priv->lecd without any protection against concurrent teardown.
Fix this by converting priv->lecd to an RCU-protected pointer: - Mark priv->lecd as __rcu in lec.h - Use rcu_assign_pointer() in lec_atm_close() and lecd_attach() for safe pointer assignment - Use rcu_access_pointer() for NULL checks that do not dereference the pointer in lec_start_xmit(), lec_push(), send_to_lecd() and lecd_attach() - Use rcu_read_lock/rcu_dereference/rcu_read_unlock in send_to_lecd(), lec_handle_bridge() and lec_atm_send() to safely access lecd - Use rcu_assign_pointer() followed by synchronize_rcu() in lec_atm_close() to ensure all readers have completed before proceeding. This is safe since lec_atm_close() is called from vcc_release() which holds lock_sock(), a sleeping lock. - Remove the manual sk_receive_queue drain from lec_atm_close() since vcc_destroy_socket() already drains it after lec_atm_close() returns.
v2: Switch from spinlock + sock_hold/put approach to RCU to properly fix the race. The v1 spinlock approach had two issues pointed out by Eric Dumazet: 1. priv->lecd was still accessed directly after releasing the lock instead of using a local copy. 2. The spinlock did not prevent packets being queued after lec_atm_close() drains sk_receive_queue since timer and workqueue paths bypass netif_stop_queue().
Note: Syzbot patch testing was attempted but the test VM terminated unexpectedly with "Connection to localhost closed by remote host", likely due to a QEMU AHCI emulation issue unrelated to this fix. Compile testing with "make W=1 net/atm/lec.o" passes cleanly.
{
"affected": [],
"aliases": [
"CVE-2026-43050"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-05-01T15:16:51Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\natm: lec: fix use-after-free in sock_def_readable()\n\nA race condition exists between lec_atm_close() setting priv-\u003elecd\nto NULL and concurrent access to priv-\u003elecd in send_to_lecd(),\nlec_handle_bridge(), and lec_atm_send(). When the socket is freed\nvia RCU while another thread is still using it, a use-after-free\noccurs in sock_def_readable() when accessing the socket\u0027s wait queue.\n\nThe root cause is that lec_atm_close() clears priv-\u003elecd without\nany synchronization, while callers dereference priv-\u003elecd without\nany protection against concurrent teardown.\n\nFix this by converting priv-\u003elecd to an RCU-protected pointer:\n- Mark priv-\u003elecd as __rcu in lec.h\n- Use rcu_assign_pointer() in lec_atm_close() and lecd_attach()\n for safe pointer assignment\n- Use rcu_access_pointer() for NULL checks that do not dereference\n the pointer in lec_start_xmit(), lec_push(), send_to_lecd() and\n lecd_attach()\n- Use rcu_read_lock/rcu_dereference/rcu_read_unlock in send_to_lecd(),\n lec_handle_bridge() and lec_atm_send() to safely access lecd\n- Use rcu_assign_pointer() followed by synchronize_rcu() in\n lec_atm_close() to ensure all readers have completed before\n proceeding. This is safe since lec_atm_close() is called from\n vcc_release() which holds lock_sock(), a sleeping lock.\n- Remove the manual sk_receive_queue drain from lec_atm_close()\n since vcc_destroy_socket() already drains it after lec_atm_close()\n returns.\n\nv2: Switch from spinlock + sock_hold/put approach to RCU to properly\n fix the race. The v1 spinlock approach had two issues pointed out\n by Eric Dumazet:\n 1. priv-\u003elecd was still accessed directly after releasing the\n lock instead of using a local copy.\n 2. The spinlock did not prevent packets being queued after\n lec_atm_close() drains sk_receive_queue since timer and\n workqueue paths bypass netif_stop_queue().\n\nNote: Syzbot patch testing was attempted but the test VM terminated\n unexpectedly with \"Connection to localhost closed by remote host\",\n likely due to a QEMU AHCI emulation issue unrelated to this fix.\n Compile testing with \"make W=1 net/atm/lec.o\" passes cleanly.",
"id": "GHSA-jhj6-5p6x-hw75",
"modified": "2026-05-07T18:30:34Z",
"published": "2026-05-01T15:30:37Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43050"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/317843d5355062020649124eb4a0d7acbcc3f53e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3989740fa4978e1d2d51ecc62be1b01093e104ad"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3e8b25f32f2f35549d03d77da030a24a45bdef5b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5fbbb1ff936d7ff9528d929c1549977e8123d8a8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/750a33f417f3d196b86375f8d9f8938bacf130fe"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/922814879542c2e397b0e9641fd36b8202a8e555"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/abc10f85a3965ac14b9ed7ad3e67b35604a63aa3"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b256d055da47258e63f8b40965f276c5f23d229a"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
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