CVE-2026-80863 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
RDMA/rxe: Fix OOB in free_rd_atomic_resources()
free_rd_atomic_resources() iterates using qp->attr.max_dest_rd_atomic. Updating max_dest_rd_atomic before freeing the old array can make the free path walk past the old allocation and trigger a slab out-of-bounds write catched by KASAN: ================================================================== BUG: KASAN: slab-out-of-bounds in free_rd_atomic_resource drivers/infiniband/sw/rxe/rxe_qp.c:180 [inline]
BUG: KASAN: slab-out-of-bounds in free_rd_atomic_resources drivers/infiniband/sw/rxe/rxe_qp.c:171 [inline]
BUG: KASAN: slab-out-of-bounds in free_rd_atomic_resources drivers/infiniband/sw/rxe/rxe_qp.c:163 [inline]
BUG: KASAN: slab-out-of-bounds in rxe_qp_from_attr+0x1e88/0x2150 drivers/infiniband/sw/rxe/rxe_qp.c:712 Write of size 4 at addr ffff88802b8dddb8 by task syz.3.451/11063
CPU: 0 UID: 0 PID: 11063 Comm: syz.3.451 Not tainted 7.1.0 #2 PREEMPT(full) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x10e/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline]
print_report+0xf7/0x600 mm/kasan/report.c:482 kasan_report+0xe4/0x120 mm/kasan/report.c:595 free_rd_atomic_resource drivers/infiniband/sw/rxe/rxe_qp.c:180 [inline]
free_rd_atomic_resources drivers/infiniband/sw/rxe/rxe_qp.c:171 [inline]
free_rd_atomic_resources drivers/infiniband/sw/rxe/rxe_qp.c:163 [inline]
rxe_qp_from_attr+0x1e88/0x2150 drivers/infiniband/sw/rxe/rxe_qp.c:712 rxe_modify_qp+0x1e2/0x530 drivers/infiniband/sw/rxe/rxe_verbs.c:623 ib_security_modify_qp+0x223/0xfa0 drivers/infiniband/core/security.c:625 _ib_modify_qp+0x333/0xec0 drivers/infiniband/core/verbs.c:1915 modify_qp+0x13ca/0x1940 drivers/infiniband/core/uverbs_cmd.c:1932 ib_uverbs_modify_qp+0xcb/0x120 drivers/infiniband/core/uverbs_cmd.c:1958 ib_uverbs_write+0xb86/0x1030 drivers/infiniband/core/uverbs_main.c:680 vfs_write+0x2aa/0x1070 fs/read_write.c:686 ksys_write+0x1f8/0x250 fs/read_write.c:740 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fefc75a70cd Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fefc8495018 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007fefc7835fa0 RCX: 00007fefc75a70cd RDX: 0000000000000078 RSI: 0000200000000240 RDI: 0000000000000007 RBP: 00007fefc764f10f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fefc7836038 R14: 00007fefc7835fa0 R15: 00007ffcf0586aa0 </TASK>
Allocated by task 11063: kasan_save_stack+0x33/0x60 mm/kasan/common.c:57 kasan_save_track+0x14/0x30 mm/kasan/common.c:78 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415 kasan_kmalloc include/linux/kasan.h:263 [inline]
__do_kmalloc_node mm/slub.c:5296 [inline]
__kmalloc_noprof+0x32a/0x850 mm/slub.c:5308 kmalloc_noprof include/linux/slab.h:954 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
alloc_rd_atomic_resources drivers/infiniband/sw/rxe/rxe_qp.c:155 [inline]
rxe_qp_from_attr+0x3f8/0x2150 drivers/infiniband/sw/rxe/rxe_qp.c:714 rxe_modify_qp+0x1e2/0x530 drivers/infiniband/sw/rxe/rxe_verbs.c:623 ib_security_modify_qp+0x223/0xfa0 drivers/infiniband/core/security.c:625 _ib_modify_qp+0x333/0xec0 drivers/infiniband/core/verbs.c:1915 modify_qp+0x13ca/0x1940 drivers/infiniband/core/uverbs_cmd.c:1932 ib_uverbs_modify_qp+0xcb/0x120 drivers/infiniband/core/uverbs_cmd.c:1958 ib_uverbs_write+0xb86/0x1030 drivers/infiniband/core/uverbs_ma ---truncated---
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Analysis
by VulDB Data Team • 09/05/2026
The Linux kernel's RDMA over Converged Ethernet (Rxe) implementation contains a critical out-of-bounds memory write vulnerability within the queue pair modification logic. This flaw is located in the free_rd_atomic_resources function, which is responsible for deallocating resources associated with remote direct memory access operations. The root cause of this issue stems from an incorrect ordering of operations during resource management. Specifically, when updating the maximum number of destination atomic operations allowed by a queue pair attribute, the kernel updates the max_dest_rd_atomic field before freeing the previously allocated array of atomic resources. This sequence error causes the deallocation routine to iterate based on the newly updated, potentially larger value rather than the size of the memory block that was originally allocated. Consequently, the free path attempts to access and write beyond the boundaries of the old allocation, triggering a slab out-of-bounds condition detected by Kernel Address Sanitizer during testing scenarios involving syzbot fuzzing tools.
From a technical perspective, this vulnerability represents a classic use-after-free or buffer over-read scenario where metadata is updated prior to data structure cleanup. The function rxe_qp_from_attr serves as the entry point for modifying queue pair attributes via user-space verbs commands. When an application requests a change in atomic operation limits through ib_uverbs_modify_qp, the kernel validates and applies these changes. However, because the old resource array is freed using the new count instead of the original allocation size, memory corruption occurs on the slab allocator level. This type of error can lead to heap metadata corruption, arbitrary code execution if an attacker can control the overwritten data, or a denial of service through kernel panic due to invalid memory access patterns. The stack trace confirms that the write operation originates from rxe_qp_from_attr and propagates through the InfiniBand core subsystem before reaching user-space interfaces.
The operational impact of this vulnerability is significant for systems relying on software-based RDMA implementations, particularly in virtualized environments where QEMU guests interact with host kernel resources via these verbs APIs. An unprivileged local attacker or a compromised guest VM could exploit this flaw to corrupt adjacent heap structures, potentially escalating privileges to root level by overwriting function pointers or object headers within the slab cache. Even without privilege escalation, such memory corruption can destabilize the entire system, causing crashes that affect other workloads running on the same host. The presence of KASAN reports indicates that while modern kernels have mitigations like stack canaries and ASLR, they do not prevent the initial exploitation vector; they only detect it post-facto during development or testing phases.
This vulnerability aligns with CWE-787: Out-of-bounds Write, as it involves writing data beyond the allocated buffer boundary due to incorrect loop bounds derived from stale or improperly updated state variables. In terms of attack vectors, this falls under MITRE ATT&CK technique T1059: Command and Scripting Interpreter if leveraged through user-space applications sending malformed ioctls, specifically within the context of Local Privilege Escalation (T1068) when heap corruption leads to control flow hijacking. The exploitability relies on precise timing or specific attribute modification sequences that trigger the race between allocation update and deallocation logic.
To mitigate this risk, system administrators should apply kernel updates provided by their distribution vendors that include the fix for free_rd_atomic_resources in drivers/infiniband/sw/rxe/rxe_qp.c. The patch ensures that the old atomic resource array is freed using its original allocated size before updating the max_dest_rd_atomic attribute to prevent iteration beyond valid memory bounds. Additionally, organizations should enable Kernel Address Sanitizer (KASAN) in their development and staging environments to detect similar off-by-one or out-of-bounds errors early in the software lifecycle. For production systems running vulnerable kernels, restricting access to InfiniBand verbs interfaces through mandatory access control policies can reduce the attack surface by limiting which users or containers are permitted to modify queue pair attributes. Regular auditing of kernel logs for KASAN reports is also recommended as an indicator of attempted exploitation activities targeting memory safety vulnerabilities in network subsystems.