CVE-2026-46029

Summary

In the Linux kernel, the following vulnerability has been resolved:

mm/slab: return NULL early from kmalloc_nolock() in NMI on UP

On UP kernels (!CONFIG_SMP), spin_trylock() is a no-op that unconditionally succeeds even when the lock is already held. As a result, kmalloc_nolock() called from NMI context can re-enter the slab allocator and acquire n->list_lock that the interrupted context is already holding, corrupting slab state.

With CONFIG_DEBUG_SPINLOCK on UP, the following BUG is triggered with the slub_kunit test module:

BUG: spinlock trylock failure on UP on CPU#0, kunit_try_catch/243 […] Call Trace: <NMI> dump_stack_lvl+0x3f/0x60 do_raw_spin_trylock+0x41/0x50 _raw_spin_trylock+0x24/0x50 get_from_partial_node+0x120/0x4d0 ___slab_alloc+0x8a/0x4c0 kmalloc_nolock_noprof+0x164/0x310 […] </NMI>

Fix this by returning NULL early when invoked from NMI on a UP kernel.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/a8d95d274be241ad21f6523bf2d6ba0d7d7e46b7
• https://git.kernel.org/stable/c/d66553204a15bdb257d9ef8aca1e12f5fbb910b2
• https://git.kernel.org/stable/c/5b31044e649e3e54c2caef135c09b371c2fbcd08

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