iommufd: Check for uptr overflow

syzkaller found that setting up a map with a user VA that wraps past zero
can trigger WARN_ONs, particularly from pin_user_pages weirdly returning 0
due to invalid arguments.

Prevent creating a pages with a uptr and size that would math overflow.

  WARNING: CPU: 0 PID: 518 at drivers/iommu/iommufd/pages.c:793 pfn_reader_user_pin+0x2e6/0x390
  Modules linked in:
  CPU: 0 PID: 518 Comm: repro Not tainted 6.3.0-rc2-eeac8ede+ #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
  RIP: 0010:pfn_reader_user_pin+0x2e6/0x390
  Code: b1 11 e9 25 fe ff ff e8 28 e4 0f ff 31 ff 48 89 de e8 2e e6 0f ff 48 85 db 74 0a e8 14 e4 0f ff e9 4d ff ff ff e8 0a e4 0f ff <0f> 0b bb f2 ff ff ff e9 3c ff ff ff e8 f9 e3 0f ff ba 01 00 00 00
  RSP: 0018:ffffc90000f9fa30 EFLAGS: 00010246
  RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff821e2b72
  RDX: 0000000000000000 RSI: ffff888014184680 RDI: 0000000000000002
  RBP: ffffc90000f9fa78 R08: 00000000000000ff R09: 0000000079de6f4e
  R10: ffffc90000f9f790 R11: ffff888014185418 R12: ffffc90000f9fc60
  R13: 0000000000000002 R14: ffff888007879800 R15: 0000000000000000
  FS:  00007f4227555740(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000020000043 CR3: 000000000e748005 CR4: 0000000000770ef0
  PKRU: 55555554
  Call Trace:
   <TASK>
   pfn_reader_next+0x14a/0x7b0
   ? interval_tree_double_span_iter_update+0x11a/0x140
   pfn_reader_first+0x140/0x1b0
   iopt_pages_rw_slow+0x71/0x280
   ? __this_cpu_preempt_check+0x20/0x30
   iopt_pages_rw_access+0x2b2/0x5b0
   iommufd_access_rw+0x19f/0x2f0
   iommufd_test+0xd11/0x16f0
   ? write_comp_data+0x2f/0x90
   iommufd_fops_ioctl+0x206/0x330
   __x64_sys_ioctl+0x10e/0x160
   ? __pfx_iommufd_fops_ioctl+0x10/0x10
   do_syscall_64+0x3b/0x90
   entry_SYSCALL_64_after_hwframe+0x72/0xdc

Cc: <stable@vger.kernel.org>
Fixes: 8d160cd4 ("iommufd: Algorithms for PFN storage")
Link: https://lore.kernel.org/r/1-v1-ceab6a4d7d7a+94-iommufd_syz_jgg@nvidia.comReviewed-by: Kevin Tian <kevin.tian@intel.com>
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/pages.c

@@ -1142,6 +1142,7 @@ struct iopt_pages *iopt_alloc_pages(void __user *uptr, unsigned long length,
 				    bool writable)
 {
 	struct iopt_pages *pages;
+	unsigned long end;
 
 	/*
 	 * The iommu API uses size_t as the length, and protect the DIV_ROUND_UP
@@ -1150,6 +1151,9 @@ struct iopt_pages *iopt_alloc_pages(void __user *uptr, unsigned long length,
 	if (length > SIZE_MAX - PAGE_SIZE || length == 0)
 		return ERR_PTR(-EINVAL);
 
+	if (check_add_overflow((unsigned long)uptr, length, &end))
+		return ERR_PTR(-EOVERFLOW);
+
 	pages = kzalloc(sizeof(*pages), GFP_KERNEL_ACCOUNT);
 	if (!pages)
 		return ERR_PTR(-ENOMEM);