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23 lines
3.4 KiB
Markdown
23 lines
3.4 KiB
Markdown
### [CVE-2024-56644](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-56644)
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### Description
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In the Linux kernel, the following vulnerability has been resolved:net/ipv6: release expired exception dst cached in socketDst objects get leaked in ip6_negative_advice() when this function isexecuted for an expired IPv6 route located in the exception table. Thereare 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 dstWhen TCP executes ip6_negative_advice() for an exception dst that hasexpired and if no other socket holds a reference to the exception dst, therefcount of the exception dst is 2, which corresponds to the incrementmade by dst_init() and the increment made by the TCP socket for which theconnection is timing out. The refcount made by the socket is neverreleased. The refcount of the dst is decremented in sk_dst_reset() butthat decrement is counteracted by a dst_hold() intentionally placed justbefore the sk_dst_reset() in ip6_negative_advice(). Afterip6_negative_advice() has finished, there is no other object tied to thedst. The socket lost its reference stored in sk_dst_cache and the dst isno longer in the exception table. The exception dst becomes a leakedobject.As a result of this dst leak, an unbalanced refcount is reported for theloopback device of a net namespace being destroyed under kernels that donot contain e5f80fcf869a ("ipv6: give an IPv6 dev to blackhole_netdev"):unregister_netdevice: waiting for lo to become free. Usage count = 2Fix the dst leak by removing the dst_hold() in ip6_negative_advice(). Thepatch that introduced the dst_hold() in ip6_negative_advice() was92f1655aa2b22 ("net: fix __dst_negative_advice() race"). But 92f1655aa2b22merely refactored the code with regards to the dst refcount so the issuewas present even before 92f1655aa2b22. The bug was introduced in54c1a859efd9f ("ipv6: Don't drop cache route entry unless timer actuallyexpired.") where the expired cached route is deleted and the sk_dst_cachemember of the socket is set to NULL by calling dst_negative_advice() butthe 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 thesk_dst_cache of the socket while decrementing the refcount of theexception dst.
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### POC
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#### Reference
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No PoCs from references.
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#### Github
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- https://github.com/bygregonline/devsec-fastapi-report
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- https://github.com/cku-heise/euvd-api-doc
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- https://github.com/w4zu/Debian_security
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