ghsa-4cgh-427p-hh6m
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
net/ipv6: release expired exception dst cached in socket
Dst objects get leaked in ip6_negative_advice() when this function is executed for an expired IPv6 route located in the exception table. There are several conditions that must be fulfilled for the leak to occur: * an ICMPv6 packet indicating a change of the MTU for the path is received, resulting in an exception dst being created * a TCP connection that uses the exception dst for routing packets must start timing out so that TCP begins retransmissions * after the exception dst expires, the FIB6 garbage collector must not run before TCP executes ip6_negative_advice() for the expired exception dst
When TCP executes ip6_negative_advice() for an exception dst that has expired and if no other socket holds a reference to the exception dst, the refcount of the exception dst is 2, which corresponds to the increment made by dst_init() and the increment made by the TCP socket for which the connection is timing out. The refcount made by the socket is never released. The refcount of the dst is decremented in sk_dst_reset() but that decrement is counteracted by a dst_hold() intentionally placed just before the sk_dst_reset() in ip6_negative_advice(). After ip6_negative_advice() has finished, there is no other object tied to the dst. The socket lost its reference stored in sk_dst_cache and the dst is no longer in the exception table. The exception dst becomes a leaked object.
As a result of this dst leak, an unbalanced refcount is reported for the loopback device of a net namespace being destroyed under kernels that do not contain e5f80fcf869a ("ipv6: give an IPv6 dev to blackhole_netdev"): unregister_netdevice: waiting for lo to become free. Usage count = 2
Fix the dst leak by removing the dst_hold() in ip6_negative_advice(). The patch that introduced the dst_hold() in ip6_negative_advice() was 92f1655aa2b22 ("net: fix __dst_negative_advice() race"). But 92f1655aa2b22 merely refactored the code with regards to the dst refcount so the issue was present even before 92f1655aa2b22. The bug was introduced in 54c1a859efd9f ("ipv6: Don't drop cache route entry unless timer actually expired.") where the expired cached route is deleted and the sk_dst_cache member of the socket is set to NULL by calling dst_negative_advice() but the refcount belonging to the socket is left unbalanced.
The IPv4 version - ipv4_negative_advice() - is not affected by this bug. When the TCP connection times out ipv4_negative_advice() merely resets the sk_dst_cache of the socket while decrementing the refcount of the exception dst.
{
"affected": [],
"aliases": [
"CVE-2024-56644"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-12-27T15:15:24Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/ipv6: release expired exception dst cached in socket\n\nDst objects get leaked in ip6_negative_advice() when this function is\nexecuted for an expired IPv6 route located in the exception table. There\nare several conditions that must be fulfilled for the leak to occur:\n* an ICMPv6 packet indicating a change of the MTU for the path is received,\n resulting in an exception dst being created\n* a TCP connection that uses the exception dst for routing packets must\n start timing out so that TCP begins retransmissions\n* after the exception dst expires, the FIB6 garbage collector must not run\n before TCP executes ip6_negative_advice() for the expired exception dst\n\nWhen TCP executes ip6_negative_advice() for an exception dst that has\nexpired and if no other socket holds a reference to the exception dst, the\nrefcount of the exception dst is 2, which corresponds to the increment\nmade by dst_init() and the increment made by the TCP socket for which the\nconnection is timing out. The refcount made by the socket is never\nreleased. The refcount of the dst is decremented in sk_dst_reset() but\nthat decrement is counteracted by a dst_hold() intentionally placed just\nbefore the sk_dst_reset() in ip6_negative_advice(). After\nip6_negative_advice() has finished, there is no other object tied to the\ndst. The socket lost its reference stored in sk_dst_cache and the dst is\nno longer in the exception table. The exception dst becomes a leaked\nobject.\n\nAs a result of this dst leak, an unbalanced refcount is reported for the\nloopback device of a net namespace being destroyed under kernels that do\nnot contain e5f80fcf869a (\"ipv6: give an IPv6 dev to blackhole_netdev\"):\nunregister_netdevice: waiting for lo to become free. Usage count = 2\n\nFix the dst leak by removing the dst_hold() in ip6_negative_advice(). The\npatch that introduced the dst_hold() in ip6_negative_advice() was\n92f1655aa2b22 (\"net: fix __dst_negative_advice() race\"). But 92f1655aa2b22\nmerely refactored the code with regards to the dst refcount so the issue\nwas present even before 92f1655aa2b22. The bug was introduced in\n54c1a859efd9f (\"ipv6: Don\u0027t drop cache route entry unless timer actually\nexpired.\") where the expired cached route is deleted and the sk_dst_cache\nmember of the socket is set to NULL by calling dst_negative_advice() but\nthe refcount belonging to the socket is left unbalanced.\n\nThe IPv4 version - ipv4_negative_advice() - is not affected by this bug.\nWhen the TCP connection times out ipv4_negative_advice() merely resets the\nsk_dst_cache of the socket while decrementing the refcount of the\nexception dst.",
"id": "GHSA-4cgh-427p-hh6m",
"modified": "2024-12-27T15:31:55Z",
"published": "2024-12-27T15:31:55Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-56644"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0b8903e6c881f72c6849d4952de742c656eb5ab9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3301ab7d5aeb0fe270f73a3d4810c9d1b6a9f045"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/535add1e9f274502209cb997801208bbe1ae6c6f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8b591bd522b71c42a82898290e35d32b482047e4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a95808252e8acc0123bacd2dff8b9af10bc145b7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b90d061345bb8cd51fece561a800bae1c95448a6"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f43d12fd0fa8ee5b9caf8a3927e10d06431764d2"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
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