Re: [PATCH] tty/vt: fix a memory leak in con_insert_unipair

[Greg Kroah-Hartman]

On Mon, Aug 10, 2020 at 07:16:48AM +0200, Jiri Slaby wrote:
> On 10. 08. 20, 0:14, James Bond wrote:
> > Syzkaller find a memory leak in con_insert_unipair:
> >     BUG: memory leak
> >     unreferenced object 0xffff88804893d100 (size 256):
> >     comm "syz-executor.3", pid 16154, jiffies 4295043307 (age 2392.340s)
> >     hex dump (first 32 bytes):
> >     80 af 88 4e 80 88 ff ff 00 a8 88 4e 80 88 ff ff  ...N.......N....
> >     80 ad 88 4e 80 88 ff ff 00 aa 88 4e 80 88 ff ff  ...N.......N....
> >     backtrace:
> >     [<00000000f76ff1de>] kmalloc include/linux/slab.h:555 [inline]
> >     [<00000000f76ff1de>] kmalloc_array include/linux/slab.h:596 [inline]
> >     [<00000000f76ff1de>] con_insert_unipair+0x9e/0x1a0 drivers/tty/vt/consolemap.c:482
> >     [<000000002f1ad7da>] con_set_unimap+0x244/0x2a0 drivers/tty/vt/consolemap.c:595
> >     [<0000000046ccb106>] do_unimap_ioctl drivers/tty/vt/vt_ioctl.c:297 [inline]
> >     [<0000000046ccb106>] vt_ioctl+0x863/0x12f0 drivers/tty/vt/vt_ioctl.c:1018
> >     [<00000000db1577ff>] tty_ioctl+0x4cd/0xa30 drivers/tty/tty_io.c:2656
> >     [<00000000e5cdf5ed>] vfs_ioctl fs/ioctl.c:48 [inline]
> >     [<00000000e5cdf5ed>] ksys_ioctl+0xa6/0xd0 fs/ioctl.c:753
> >     [<00000000fb4aa12c>] __do_sys_ioctl fs/ioctl.c:762 [inline]
> >     [<00000000fb4aa12c>] __se_sys_ioctl fs/ioctl.c:760 [inline]
> >     [<00000000fb4aa12c>] __x64_sys_ioctl+0x1a/0x20 fs/ioctl.c:760
> >     [<00000000f561f260>] do_syscall_64+0x4c/0xe0 arch/x86/entry/common.c:384
> >     [<0000000056206928>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >     BUG: leak checking failed
> > 
> > To fix this issue, we need to release the pointer p1 when the call of
> > the function kmalloc_array fail.
> 
> This reminds me of:
> commit 15b3cd8ef46ad1b100e0d3c7e38774f330726820
> Author: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> Date:   Tue Jun 4 19:00:39 2019 +0100
> 
>     Revert "consolemap: Fix a memory leaking bug in
> drivers/tty/vt/consolemap.c"
> 
>     This reverts commit 84ecc2f6eb1cb12e6d44818f94fa49b50f06e6ac.
> 
> 
> 
> So NACK.

I have a whole talk just about the "fun" involved with that change:
	https://kernel-recipes.org/en/2019/talks/cves-are-dead-long-live-the-cve/

> Do we have some annotations for this instead?

We need something there, a comment saying "this is fine, don't touch
it!" or something like that?  We need that in a few other places in the
vt code as well.

> > Signed-off-by: James Bond <jameslouisebond@xxxxxxxxx>

Nice name...

James, can you mark this syzbot report as "invalid" or something like
that please so that this does not come up again and again.

thanks,

greg k-h