CVE-2024-26785

In the Linux kernel, the following vulnerability has been resolved:
iommufd: Fix protection fault in iommufd_test_syz_conv_iova Syzkaller
reported the following bug: general protection fault, probably for
non-canonical address 0xdffffc0000000038: 0000 [#1] SMP KASAN KASAN:
null-ptr-deref in range [0x00000000000001c0-0x00000000000001c7] Call Trace:
lock_acquire lock_acquire+0x1ce/0x4f0 down_read+0x93/0x4a0
iommufd_test_syz_conv_iova+0x56/0x1f0
iommufd_test_access_rw.isra.0+0x2ec/0x390 iommufd_test+0x1058/0x1e30
iommufd_fops_ioctl+0x381/0x510 vfs_ioctl __do_sys_ioctl __se_sys_ioctl
__x64_sys_ioctl+0x170/0x1e0 do_syscall_x64 do_syscall_64+0x71/0x140 This is
because the new iommufd_access_change_ioas() sets access->ioas to NULL
during its process, so the lock might be gone in a concurrent racing
context. Fix this by doing the same access->ioas sanity as
iommufd_access_rw() and iommufd_access_pin_pages() functions do.