- Description
- In the Linux kernel, the following vulnerability has been resolved:
net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop
When a standalone IPv6 nexthop object is created with a loopback device
(e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies
it as a reject route. This is because nexthop objects have no destination
prefix (fc_dst=::), causing fib6_is_reject() to match any loopback
nexthop. The reject path skips fib_nh_common_init(), leaving
nhc_pcpu_rth_output unallocated. If an IPv4 route later references this
nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and
panics.
Simplify the check in fib6_nh_init() to only match explicit reject
routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback
promotion heuristic in fib6_is_reject() is handled separately by
ip6_route_info_create_nh(). After this change, the three cases behave
as follows:
1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"):
RTF_REJECT is set, enters reject path, skips fib_nh_common_init().
No behavior change.
2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"):
RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
called. ip6_route_info_create_nh() still promotes it to reject
afterward. nhc_pcpu_rth_output is allocated but unused, which is
harmless.
3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"):
RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
called. nhc_pcpu_rth_output is properly allocated, fixing the crash
when IPv4 routes reference this nexthop.
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- NVD status
- Analyzed
- Products
- linux_kernel
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