CVE-2026-80817: iommu/iommufd: Fix NULL pointer deref in iommufd_ioas_change_process when racing with iopt_map_file_pages

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

iommu/iommufd: Fix NULL pointer deref in iommufdioaschangeprocess when racing with ioptmapfilepages

iommufdioaschangeprocess() iterates every IOAS area while only holding every IOAS iovarwsem, so it assumes every area has a non-NULL pages pointer. That assumption can be false when it runs concurrently with ioptmapfilepages().

ioptmappages() executes in two phases. It first creates the area and inserts it into the interval tree under iovarwsem, with area->pages still NULL. It then drops iovarwsem and later fills area->pages under domainsrwsem. This leaves a window between area creation and area->pages fill where a concurrent iommufdioaschangeprocess() 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: errorcode(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, archcaps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:iommufdioaschangeprocess+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> iommufdfopsioctl+0x287/0x400 drivers/iommu/iommufd/main.c:533 vfsioctl fs/ioctl.c:51 [inline] dosysioctl fs/ioctl.c:597 [inline] sesysioctl fs/ioctl.c:583 [inline] x64sysioctl+0x120/0x170 fs/ioctl.c:583 x64syscall+0x1092/0x1fb0 arch/x86/include/generated/asm/syscalls64.h:17 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0x10a/0x680 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+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 ORIGRAX: 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:iommufdioaschangeprocess+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---