This is a note to let you know that I've just added the patch titled
vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
vc_screen-move-load-of-struct-vc_data-pointer-in-vcs.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1d3455b2094ff80bc63e8a92a0398e0e67f74c2c
Author: George Kennedy <george.kennedy@xxxxxxxxxx>
Date: Tue Jan 24 11:16:54 2023 -0500
vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF
[ Upstream commit 226fae124b2dac217ea5436060d623ff3385bc34 ]
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@xxxxxxxxxxxxxxxx>
Suggested-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
Link: https://lore.kernel.org/r/1674577014-12374-1-git-send-email-george.kennedy@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index 2fb509d57e88..03fe692d940b 100644
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -247,10 +247,6 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
uni_mode = use_unicode(inode);
attr = use_attributes(inode);
- ret = -ENXIO;
- vc = vcs_vc(inode, &viewed);
- if (!vc)
- goto unlock_out;
ret = -EINVAL;
if (pos < 0)
@@ -270,6 +266,11 @@ 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.
