Findings

CVE-2026-23316

In the Linux kernel, the following vulnerability has been resolved: net: ipv4: fix ARM64 alignment fault in multipath hash seed contains two u32 fields (user_seed and…

Published Mar 25, 2026 · updated Jun 17, 2026 · linux linux kernel

In the Linux kernel, the following vulnerability has been resolved: net: ipv4: fix ARM64 alignment fault in multipath hash seed contains two u32 fields (user_seed and mp_seed), making it an 8-byte structure with a 4-byte alignment requirement. In , the code evaluates the entire struct atomically via : mp_seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).mp_seed; While this silently works on GCC by falling back to unaligned regular loads which the ARM64 kernel tolerates, it causes a fatal kernel panic when compiled with Clang and LTO enabled. Commit e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y") strengthens to use Load-Acquire instructions ( / ) to prevent compiler reordering bugs under Clang LTO. Since the macro evaluates the full 8-byte struct, Clang emits a 64-bit instruction. ARM64 architecture strictly requires to be naturally aligned, thus executing it on a 4-byte aligned address triggers a strict Alignment Fault (FSC = 0x21). Fix the read side by moving the directly to the member, which emits a safe 32-bit . Furthermore, Eric Dumazet pointed out that on the entire struct in is also flawed. Analysis shows that Clang splits this 8-byte write into two separate 32-bit instructions. While this avoids an alignment fault, it destroys atomicity and exposes a tear-write vulnerability. Fix this by explicitly splitting the write into two 32-bit operations. Finally, add the missing when reading in to ensure proper pairing and concurrency safety.