In the Linux kernel, the following vulnerability has been resolved:
mm/mempolicy: fix sleeping allocation in alloc_pages_bulk_weighted_interleave()
syzbot reported a sleeping function called from invalid context splat in
bucket_table_alloc().
When rhashtable_insert_slow() rehashes the table under rcu_read_lock(), it
calls bucket_table_alloc(..., GFP_ATOMIC | __GFP_NOWARN). If the bucket
table allocation uses vmalloc, __vmalloc_node_range_noprof() invokes
vm_area_alloc_pages() -> alloc_pages_bulk_mempolicy_noprof() with the
passed GFP_ATOMIC flags.
If the current task has an MPOL_WEIGHTED_INTERLEAVE mempolicy,
alloc_pages_bulk_weighted_interleave() is called and currently hardcodes
GFP_KERNEL when allocating the temporary weights array, triggering a
might_alloc() splat in atomic/RCU contexts.
Pass the gfp flags (masked with GFP_RECLAIM_MASK to strip page-allocator
zone modifiers like __GFP_HIGHMEM) received by
alloc_pages_bulk_weighted_interleave() to kmalloc() instead of hardcoding
GFP_KERNEL. Since the weights buffer is immediately initialized in full,
kmalloc() is sufficient.
CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 7.8
AV:L - Triggering requires set_mempolicy(MPOL_WEIGHTED_INTERLEAVE) on the attacker's task and a local syscall that grows an rhashtable until GFP_ATOMIC kvmalloc falls back to vmalloc (nftables hash sets, tc flower, BPF rhashtable maps); softirq/packet paths use default_policy via in_interrupt() and cannot apply the attacker's mempolicy.
AC:L - The attacker fully controls setup: set_mempolicy on their own task, insert enough rhashtable elements for a >PAGE_SIZE bucket table, and apply memory pressure so GFP_ATOMIC kmalloc fails and kvmalloc uses vmalloc; CONFIG_NUMA is standard on x86_64/arm64 distro and cloud kernels, and no attacker-uncontrollable race is required.
PR:L - set_mempolicy() has no capability check, and the rhashtable rehash path is reachable by an unprivileged user via nftables or tc in a user+net namespace where CAP_NET_ADMIN is namespace-local; init-namespace root is not required.
UI:N - The attacker sets their own mempolicy and drives the rhashtable inserts themselves; no victim action such as mounting a filesystem or opening a file is required.
S:U - The illegal GFP_KERNEL allocation and any resulting RCU use-after-free of the rhashtable bucket table stay inside the host kernel's memory-management authority; this is standard in-kernel impact, not a VM, IOMMU, or sandbox boundary crossing.
C:H - Sleeping under rcu_read_lock() in rhashtable_insert_slow() on non-PREEMPT_RCU kernels can let the grace period complete and free the old bucket table before rhashtable_rehash_attach() uses it, yielding a use-after-free read of kernel heap.
I:H - The same RCU-break UAF lets rhashtable_rehash_attach() cmpxchg old_tbl->future_tbl on a freed table, which is an attacker-sprayable kernel write primitive via heap reuse rather than a clean failure.
A:H - GFP_KERNEL under rcu_read_lock produces a sleeping-from-invalid-context BUG/WARN (panic with panic_on_warn), can RCU-stall or deadlock if reclaim actually sleeps, and the bucket-table UAF can oops the kernel.
| Attack Vector |
Local |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
Low |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:L - Triggering requires set_mempolicy(MPOL_WEIGHTED_INTERLEAVE) on the attacker's task and a local syscall that grows an rhashtable until GFP_ATOMIC kvmalloc falls back to vmalloc (nftables hash sets, tc flower, BPF rhashtable maps); softirq/packet paths use default_policy via in_interrupt() and cannot apply the attacker's mempolicy.
AC:L - The attacker fully controls setup: set_mempolicy on their own task, insert enough rhashtable elements for a >PAGE_SIZE bucket table, and apply memory pressure so GFP_ATOMIC kmalloc fails and kvmalloc uses vmalloc; CONFIG_NUMA is standard on x86_64/arm64 distro and cloud kernels, and no attacker-uncontrollable race is required.
PR:L - set_mempolicy() has no capability check, and the rhashtable rehash path is reachable by an unprivileged user via nftables or tc in a user+net namespace where CAP_NET_ADMIN is namespace-local; init-namespace root is not required.
UI:N - The attacker sets their own mempolicy and drives the rhashtable inserts themselves; no victim action such as mounting a filesystem or opening a file is required.
S:U - The illegal GFP_KERNEL allocation and any resulting RCU use-after-free of the rhashtable bucket table stay inside the host kernel's memory-management authority; this is standard in-kernel impact, not a VM, IOMMU, or sandbox boundary crossing.
C:H - Sleeping under rcu_read_lock() in rhashtable_insert_slow() on non-PREEMPT_RCU kernels can let the grace period complete and free the old bucket table before rhashtable_rehash_attach() uses it, yielding a use-after-free read of kernel heap.
I:H - The same RCU-break UAF lets rhashtable_rehash_attach() cmpxchg old_tbl->future_tbl on a freed table, which is an attacker-sprayable kernel write primitive via heap reuse rather than a clean failure.
A:H - GFP_KERNEL under rcu_read_lock produces a sleeping-from-invalid-context BUG/WARN (panic with panic_on_warn), can RCU-stall or deadlock if reclaim actually sleeps, and the bucket-table UAF can oops the kernel.
CVSS 3.1