Affected: Linux

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…