From: Tyler Hicks tyhicks@canonical.com
This patch is a simplified fix to address a use-after-free in 4.14.x and 4.19.x stable kernels. The flaw is already fixed upstream, starting in 5.2, by commit 7dc40713618c ("drm/i915: Introduce a mutex for file_priv->context_idr") as part of a more complex patch series that isn't appropriate for backporting to stable kernels.
Expand mutex coverage, while destroying the GEM context, to include the GEM context lookup step. This fixes a use-after-free detected by KASAN:
================================================================== BUG: KASAN: use-after-free in i915_ppgtt_close+0x2ca/0x2f0 Write of size 1 at addr ffff8881368a8368 by task i915-poc/3124
CPU: 0 PID: 3124 Comm: i915-poc Not tainted 4.14.164 #1 Hardware name: HP HP Elite x2 1012 G1 /80FC, BIOS N85 Ver. 01.20 04/05/2017 Call Trace: dump_stack+0xcd/0x12e ? _atomic_dec_and_lock+0x1b2/0x1b2 ? i915_ppgtt_close+0x2ca/0x2f0 ? printk+0x8f/0xab ? show_regs_print_info+0x53/0x53 ? i915_ppgtt_close+0x2ca/0x2f0 print_address_description+0x65/0x270 ? i915_ppgtt_close+0x2ca/0x2f0 kasan_report+0x251/0x340 i915_ppgtt_close+0x2ca/0x2f0 ? __radix_tree_insert+0x3f0/0x3f0 ? i915_ppgtt_init_hw+0x7c0/0x7c0 context_close+0x42e/0x680 ? i915_gem_context_release+0x230/0x230 ? kasan_kmalloc+0xa0/0xd0 ? radix_tree_delete_item+0x1d4/0x250 ? radix_tree_lookup+0x10/0x10 ? inet_recvmsg+0x4b0/0x4b0 ? kasan_slab_free+0x88/0xc0 i915_gem_context_destroy_ioctl+0x236/0x300 ? i915_gem_context_create_ioctl+0x360/0x360 ? drm_dev_printk+0x1d0/0x1d0 ? memcpy+0x34/0x50 ? i915_gem_context_create_ioctl+0x360/0x360 drm_ioctl_kernel+0x1b0/0x2b0 ? drm_ioctl_permit+0x2a0/0x2a0 ? avc_ss_reset+0xd0/0xd0 drm_ioctl+0x6fe/0xa20 ? i915_gem_context_create_ioctl+0x360/0x360 ? drm_getstats+0x20/0x20 ? put_unused_fd+0x260/0x260 do_vfs_ioctl+0x189/0x12d0 ? ioctl_preallocate+0x280/0x280 ? selinux_file_ioctl+0x3a7/0x680 ? selinux_bprm_set_creds+0xe30/0xe30 ? security_file_ioctl+0x69/0xa0 ? selinux_bprm_set_creds+0xe30/0xe30 SyS_ioctl+0x6f/0x80 ? __sys_sendmmsg+0x4a0/0x4a0 ? do_vfs_ioctl+0x12d0/0x12d0 do_syscall_64+0x214/0x5f0 ? __switch_to_asm+0x31/0x60 ? __switch_to_asm+0x25/0x60 ? __switch_to_asm+0x31/0x60 ? syscall_return_slowpath+0x2c0/0x2c0 ? copy_overflow+0x20/0x20 ? __switch_to_asm+0x25/0x60 ? syscall_return_via_sysret+0x2a/0x7a ? prepare_exit_to_usermode+0x200/0x200 ? __switch_to_asm+0x31/0x60 ? __switch_to_asm+0x31/0x60 ? __switch_to_asm+0x25/0x60 ? __switch_to_asm+0x25/0x60 ? __switch_to_asm+0x31/0x60 ? __switch_to_asm+0x25/0x60 ? __switch_to_asm+0x31/0x60 ? __switch_to_asm+0x31/0x60 ? __switch_to_asm+0x25/0x60 entry_SYSCALL_64_after_hwframe+0x3d/0xa2 RIP: 0033:0x7f7fda5115d7 RSP: 002b:00007f7eec317ec8 EFLAGS: 00000286 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f7fda5115d7 RDX: 000055b306db9188 RSI: 000000004008646e RDI: 0000000000000003 RBP: 00007f7eec317ef0 R08: 00007f7eec318700 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000286 R12: 00007f7eec317fc0 R13: 0000000000000000 R14: 0000000000000000 R15: 00007ffd8007ade0
Allocated by task 2898: save_stack+0x32/0xb0 kasan_kmalloc+0xa0/0xd0 kmem_cache_alloc_trace+0x5e/0x180 i915_ppgtt_create+0xab/0x2510 i915_gem_create_context+0x981/0xf90 i915_gem_context_create_ioctl+0x1d7/0x360 drm_ioctl_kernel+0x1b0/0x2b0 drm_ioctl+0x6fe/0xa20 do_vfs_ioctl+0x189/0x12d0 SyS_ioctl+0x6f/0x80 do_syscall_64+0x214/0x5f0 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
Freed by task 104: save_stack+0x32/0xb0 kasan_slab_free+0x72/0xc0 kfree+0x88/0x190 i915_ppgtt_release+0x24e/0x460 i915_gem_context_free+0x90/0x480 contexts_free_worker+0x54/0x80 process_one_work+0x876/0x14e0 worker_thread+0x1b8/0xfd0 kthread+0x2f8/0x3c0 ret_from_fork+0x35/0x40
The buggy address belongs to the object at ffff8881368a8000 which belongs to the cache kmalloc-8192 of size 8192 The buggy address is located 872 bytes inside of 8192-byte region [ffff8881368a8000, ffff8881368aa000) The buggy address belongs to the page: page:ffffea0004da2a00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 flags: 0x200000000008100(slab|head) raw: 0200000000008100 0000000000000000 0000000000000000 0000000100030003 raw: dead000000000100 dead000000000200 ffff88822a002280 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff8881368a8200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881368a8280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881368a8300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^ ffff8881368a8380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881368a8400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================
Fixes: 1acfc104cdf8 ("drm/i915: Enable rcu-only context lookups") Reported-by: 罗权 luoquan@qianxin.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Jon Bloomfield jon.bloomfield@intel.com Cc: stable@vger.kernel.org # 4.14.x Cc: stable@vger.kernel.org # 4.19.x Signed-off-by: Tyler Hicks tyhicks@canonical.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/i915_gem_context.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
--- a/drivers/gpu/drm/i915/i915_gem_context.c +++ b/drivers/gpu/drm/i915/i915_gem_context.c @@ -770,18 +770,19 @@ int i915_gem_context_destroy_ioctl(struc if (args->ctx_id == DEFAULT_CONTEXT_HANDLE) return -ENOENT;
+ ret = i915_mutex_lock_interruptible(dev); + if (ret) + return ret; + ctx = i915_gem_context_lookup(file_priv, args->ctx_id); - if (!ctx) + if (!ctx) { + mutex_unlock(&dev->struct_mutex); return -ENOENT; - - ret = mutex_lock_interruptible(&dev->struct_mutex); - if (ret) - goto out; + }
__destroy_hw_context(ctx, file_priv); mutex_unlock(&dev->struct_mutex);
-out: i915_gem_context_put(ctx); return 0; }