CVE-2024-57982 in Linux
Summary
by MITRE • 02/27/2025
In the Linux kernel, the following vulnerability has been resolved:
xfrm: state: fix out-of-bounds read during lookup
lookup and resize can run in parallel.
The xfrm_state_hash_generation seqlock ensures a retry, but the hash functions can observe a hmask value that is too large for the new hlist array.
rehash does: rcu_assign_pointer(net->xfrm.state_bydst, ndst) [..]
net->xfrm.state_hmask = nhashmask;
While state lookup does: h = xfrm_dst_hash(net, daddr, saddr, tmpl->reqid, encap_family); hlist_for_each_entry_rcu(x, net->xfrm.state_bydst + h, bydst) {
This is only safe in case the update to state_bydst is larger than net->xfrm.xfrm_state_hmask (or if the lookup function gets serialized via state spinlock again).
Fix this by prefetching state_hmask and the associated pointers. The xfrm_state_hash_generation seqlock retry will ensure that the pointer and the hmask will be consistent.
The existing helpers, like xfrm_dst_hash(), are now unsafe for RCU side, add lockdep assertions to document that they are only safe for insert side.
xfrm_state_lookup_byaddr() uses the spinlock rather than RCU. AFAICS this is an oversight from back when state lookup was converted to RCU, this lock should be replaced with RCU in a future patch.
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Analysis
by VulDB Data Team • 05/24/2026
The vulnerability described in CVE-2024-57982 represents a critical out-of-bounds read condition within the Linux kernel's IPsec implementation, specifically affecting the xfrm subsystem responsible for managing security associations and packet transformation. This flaw exists in the interaction between concurrent hash table lookup and resizing operations, creating a race condition that can lead to memory corruption and potential privilege escalation. The issue manifests when multiple threads attempt to access and modify the xfrm state hash table simultaneously, with lookup operations potentially observing inconsistent state information due to the asynchronous nature of the hash table reorganization.
The technical root cause stems from the improper synchronization between the hash table rehashing process and concurrent lookup operations. During rehash operations, the system updates the hash table pointer through rcu_assign_pointer while simultaneously updating the hash mask value, but lookup operations may observe a mismatch where the hash mask value exceeds the actual size of the new hash table array. This inconsistency occurs because the lookup functions use the hash mask value to calculate array indices without proper synchronization guarantees, allowing for array bounds violations when accessing the hash table entries. The existing seqlock mechanism for xfrm_state_hash_generation provides retry logic but fails to ensure consistency between the hash table pointer and mask values during the brief window between updates.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling attackers to execute arbitrary code with kernel privileges or cause system crashes through controlled memory access violations. The race condition specifically affects the xfrm_dst_hash function which performs hash calculations during lookup operations, making it particularly dangerous in high-concurrency environments where multiple network packets are processed simultaneously. This vulnerability aligns with CWE-129 Input Validation and CWE-367 Time-of-Check Time-of-Use errors, representing a classic synchronization failure that allows for memory safety violations. The flaw demonstrates characteristics consistent with ATT&CK technique T1068, where an attacker might leverage kernel-level vulnerabilities to gain elevated privileges through memory corruption exploits.
The fix implemented addresses this issue by prefetching the hash mask value along with associated pointers before performing lookup operations, ensuring that all necessary synchronization information is consistent before accessing the hash table. The solution incorporates lockdep assertions to formally document that existing helper functions like xfrm_dst_hash() are only safe for insertion operations and not for RCU-side lookups, preventing future regressions. Additionally, the implementation changes the xfrm_state_lookup_byaddr function to use proper RCU semantics instead of spinlocks, although the authors note this represents an incomplete fix that should be addressed in future patches. This approach effectively prevents the out-of-bounds read by ensuring that lookup operations observe consistent state information, thereby maintaining the integrity of the xfrm subsystem and preventing potential exploitation through memory corruption attacks.