CVE-2026-80817 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/iommufd: Fix NULL pointer deref in iommufd_ioas_change_process when racing with iopt_map_file_pages
iommufd_ioas_change_process() iterates every IOAS area while only holding every IOAS iova_rwsem, so it assumes every area has a non-NULL pages pointer. That assumption can be false when it runs concurrently with iopt_map_file_pages().
iopt_map_pages() executes in two phases. It first creates the area and inserts it into the interval tree under iova_rwsem, with area->pages still NULL. It then drops iova_rwsem and later fills area->pages under domains_rwsem. This leaves a window between area creation and area->pages fill where a concurrent iommufd_ioas_change_process() can observe the area and dereference a NULL area->pages pointer, leading to a NULL pointer dereference:
BUG: kernel NULL pointer dereference, address: 00000000000000c0 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 4b655067 P4D 4b655067 PUD 0 Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 11841 Comm: syz.1.628 Not tainted 7.1.0 #3 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 RIP: 0010:iommufd_ioas_change_process+0x419/0xd50 drivers/iommu/iommufd/ioas.c:538 Code: 48 89 c3 48 85 c0 0f 84 cc 00 00 00 e8 10 f5 cb fd 48 8d 7b 68 e8 a7 b5 eb fd 48 8b 6b 68 48 8d bd c0 00 00 00 e8 17 b2 eb fd <8b> ad c0 00 00 00 bf 01 00 00 00 89 ee e8 85 ef cb fd 83 fd 01 74 RSP: 0018:ffffc90015c17d28 EFLAGS: 00010246 RAX: ffff8880186d5328 RBX: ffff88801d25e240 RCX: 0000000080000000 RDX: 00000000000002d7 RSI: ffffffff83ba9e10 RDI: 00000000000000c0 RBP: 0000000000000000 R08: ffffffff8e781eb8 R09: 0000000000000000 R10: 00000000000000c0 R11: ffffffff83ba9e29 R12: ffff88802e216008 R13: ffff88802e216000 R14: 0000000000000001 R15: 0000000000000000 FS: 00007f4aea3f66c0(0000) GS:ffff8880b1fa1000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000000c0 CR3: 000000004b75c000 CR4: 0000000000350ef0 Call Trace: <TASK> iommufd_fops_ioctl+0x287/0x400 drivers/iommu/iommufd/main.c:533 vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x120/0x170 fs/ioctl.c:583 x64_sys_call+0x1092/0x1fb0 arch/x86/include/generated/asm/syscalls_64.h:17 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x10a/0x680 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f4aec1a82bd 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:00007f4aea3f6018 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f4aec436090 RCX: 00007f4aec1a82bd RDX: 0000200000000180 RSI: 0000000000003b92 RDI: 0000000000000003 RBP: 00007f4aec250295 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f4aec436128 R14: 00007f4aec436090 R15: 00007ffd04ef23e0 </TASK> Modules linked in: CR2: 00000000000000c0 ---[ end trace 0000000000000000 ]---
RIP: 0010:iommufd_ioas_change_process+0x419/0xd50 drivers/iommu/iommufd/ioas.c:538 Code: 48 89 c3 48 85 c0 0f 84 cc 00 00 00 e8 10 f5 cb fd 48 8d 7b 68 e8 a7 b5 eb fd 48 8b 6b 68 48 8d bd c0 00 00 00 e8 17 b2 eb fd <8b> ad c0 00 00 00 bf 01 00 00 00 89 ee e8 85 ef cb fd 83 fd 01 74 RSP: 0018:ffffc90015c17d28 EFLAGS: 00010246 RAX: ffff8880186d5328 RBX: ffff88801d25e240 RCX: 0000000080000000 RDX: 00000000000002d7 RSI: ffffffff83ba9e10 RDI: 00000000000000c0 RBP: 0000000000000000 R08: ffffffff8e781eb8 R09: 0000000000000000 R10: 00000000000000c0 R11: ffffffff83ba9e29 R12: ffff88802e216008 R13: ffff88802e216000 R14: 0000000000000001 R15: 0000000000000000 FS: 00007f4aea3f66c0(000 ---truncated---
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel's IOMMU user-space API subsystem, specifically within the iommufd driver, contains a critical race condition vulnerability that leads to a NULL pointer dereference. This flaw resides in the function iommufd_ioas_change_process, which is responsible for iterating through Input/Output Address Space areas to perform state changes or validations. The root cause of this issue stems from an incorrect assumption regarding thread safety and data initialization states during concurrent operations. Specifically, the function iterates over every IOAS area while holding only the iova_rwsem read lock. It assumes that any area encountered during this iteration will have a fully initialized pages pointer. However, this assumption fails when the operation races with another kernel routine called iopt_map_file_pages, which is tasked with mapping file-backed memory into an IOMMU domain.
The technical flaw arises from the two-phase execution model of iopt_map_pages and its derivative functions like iopt_map_file_pages. In the first phase, a new IOAS area structure is created and inserted into the interval tree under the protection of the iova_rwsem lock. At this precise moment, the pages pointer within the newly created area remains NULL because the actual memory mapping has not yet occurred. The function then releases the iova_rwsem to acquire domains_rwsem for the second phase, where it populates the area->pages field with valid page references. This creates a narrow but exploitable time window between the insertion of the uninitialized area into the tree and the completion of its initialization. During this interval, if another thread executes iommufd_ioas_change_process while holding only the read lock on iova_rwsem, it can traverse the interval tree, encounter the partially initialized area, and attempt to dereference the NULL pages pointer.
This race condition results in a kernel panic due to a supervisor mode read access violation at address zero or near-zero offsets, as evidenced by the provided crash trace showing RIP pointing into iommufd_ioas_change_process with RDI containing 0x00000000000000c0. The operational impact of this vulnerability is significant for systems relying on IOMMU passthrough capabilities or virtualization environments where user-space applications frequently interact with the kernel's memory management subsystem via ioctls. An attacker who can trigger concurrent calls to these specific IOCTLs could cause a denial of service by crashing the host system, potentially disrupting all running workloads and requiring a full reboot. In more complex scenarios involving privilege escalation vectors or further exploitation chains following a crash, this instability could lead to broader security compromises depending on the surrounding kernel state and mitigations like KASLR or SMEP/SMAP.
From a classification perspective, this vulnerability aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). The specific failure mode of accessing an uninitialized resource due to timing issues also relates closely to CWE-824: Access of Uninitialized Pointer. In the context of the MITRE ATT&CK framework, this vulnerability facilitates Denial of Service against critical infrastructure components and could be categorized under T1595: Active Scanning or potentially as a precursor for more advanced attacks if combined with other flaws in the IOMMU subsystem to bypass isolation boundaries between guest virtual machines and host memory.
To mitigate this risk, developers must ensure that all shared data structures are fully initialized before they become visible to concurrent readers. The fix involves adjusting the locking strategy within iopt_map_file_pages or modifying iommufd_ioas_change_process to handle uninitialized areas gracefully. A robust solution would involve either deferring the insertion of the area into the interval tree until after pages have been populated, thereby eliminating the window where a NULL pointer is visible under the read lock, or adding explicit checks within the iteration loop in iommufd_ioas_change_process to skip areas that do not yet have valid page mappings. System administrators should apply kernel updates containing this patch immediately to prevent potential system instability and maintain the integrity of virtualization environments dependent on secure IOMMU operations.