From: George Kennedy george.kennedy@oracle.com

commit 226fae124b2dac217ea5436060d623ff3385bc34 upstream.

After a call to console_unlock() in vcs_read() the vc_data struct can be freed by vc_deallocate(). Because of that, the struct vc_data pointer load must be done at the top of while loop in vcs_read() to avoid a UAF when vcs_size() is called.

Syzkaller reported a UAF in vcs_size().

BUG: KASAN: use-after-free in vcs_size (drivers/tty/vt/vc_screen.c:215) Read of size 4 at addr ffff8881137479a8 by task 4a005ed81e27e65/1537

CPU: 0 PID: 1537 Comm: 4a005ed81e27e65 Not tainted 6.2.0-rc5 #1 Hardware name: Red Hat KVM, BIOS 1.15.0-2.module Call Trace: <TASK> __asan_report_load4_noabort (mm/kasan/report_generic.c:350) vcs_size (drivers/tty/vt/vc_screen.c:215) vcs_read (drivers/tty/vt/vc_screen.c:415) vfs_read (fs/read_write.c:468 fs/read_write.c:450) ... </TASK>

Allocated by task 1191: ... kmalloc_trace (mm/slab_common.c:1069) vc_allocate (./include/linux/slab.h:580 ./include/linux/slab.h:720 drivers/tty/vt/vt.c:1128 drivers/tty/vt/vt.c:1108) con_install (drivers/tty/vt/vt.c:3383) tty_init_dev (drivers/tty/tty_io.c:1301 drivers/tty/tty_io.c:1413 drivers/tty/tty_io.c:1390) tty_open (drivers/tty/tty_io.c:2080 drivers/tty/tty_io.c:2126) chrdev_open (fs/char_dev.c:415) do_dentry_open (fs/open.c:883) vfs_open (fs/open.c:1014) ...

Freed by task 1548: ... kfree (mm/slab_common.c:1021) vc_port_destruct (drivers/tty/vt/vt.c:1094) tty_port_destructor (drivers/tty/tty_port.c:296) tty_port_put (drivers/tty/tty_port.c:312) vt_disallocate_all (drivers/tty/vt/vt_ioctl.c:662 (discriminator 2)) vt_ioctl (drivers/tty/vt/vt_ioctl.c:903) tty_ioctl (drivers/tty/tty_io.c:2776) ...

The buggy address belongs to the object at ffff888113747800 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 424 bytes inside of 1024-byte region [ffff888113747800, ffff888113747c00)

The buggy address belongs to the physical page: page:00000000b3fe6c7c refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x113740 head:00000000b3fe6c7c order:3 compound_mapcount:0 subpages_mapcount:0 compound_pincount:0 anon flags: 0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff) raw: 0017ffffc0010200 ffff888100042dc0 0000000000000000 dead000000000001 raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff888113747880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888113747900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

ffff888113747980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^ ffff888113747a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888113747a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== Disabling lock debugging due to kernel taint

Fixes: ac751efa6a0d ("console: rename acquire/release_console_sem() to console_lock/unlock()") Reported-by: syzkaller syzkaller@googlegroups.com Suggested-by: Jiri Slaby jirislaby@kernel.org Signed-off-by: George Kennedy george.kennedy@oracle.com Link: https://lore.kernel.org/r/1674577014-12374-1-git-send-email-george.kennedy@o... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [ 4.14: Adjust context ] Signed-off-by: Suraj Jitindar Singh surajjs@amazon.com --- drivers/tty/vt/vc_screen.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c index 42c9ef64108f..aa67730f5cc6 100644 --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c @@ -219,10 +219,6 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) console_lock();

attr = (currcons & 128); - ret = -ENXIO; - vc = vcs_vc(inode, &viewed); - if (!vc) - goto unlock_out;

ret = -EINVAL; if (pos < 0) @@ -238,6 +234,11 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) ssize_t orig_count; long p = pos;

+ ret = -ENXIO; + vc = vcs_vc(inode, &viewed); + if (!vc) + goto unlock_out; + /* Check whether we are above size each round, * as copy_to_user at the end of this loop * could sleep.