Re: [PATCH 4.4 22/32] net: hso: fix null-ptr-deref during tty device unregistration

[Johan Hovold]

On Mon, Apr 26, 2021 at 09:29:20AM +0200, Greg Kroah-Hartman wrote:
> From: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>
> 
> commit 8a12f8836145ffe37e9c8733dce18c22fb668b66 upstream
> 
> Multiple ttys try to claim the same the minor number causing a double
> unregistration of the same device. The first unregistration succeeds
> but the next one results in a null-ptr-deref.
> 
> The get_free_serial_index() function returns an available minor number
> but doesn't assign it immediately. The assignment is done by the caller
> later. But before this assignment, calls to get_free_serial_index()
> would return the same minor number.
> 
> Fix this by modifying get_free_serial_index to assign the minor number
> immediately after one is found to be and rename it to obtain_minor()
> to better reflect what it does. Similary, rename set_serial_by_index()
> to release_minor() and modify it to free up the minor number of the
> given hso_serial. Every obtain_minor() should have corresponding
> release_minor() call.
> 
> Fixes: 72dc1c096c705 ("HSO: add option hso driver")
> Reported-by: syzbot+c49fe6089f295a05e6f8@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+c49fe6089f295a05e6f8@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> [sudip: adjust context]
> Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/net/usb/hso.c |   33 ++++++++++++---------------------
>  1 file changed, 12 insertions(+), 21 deletions(-)

We just got a regression report against this one. Perhaps better to hold
off until that has been resolved.

	https://lore.kernel.org/r/20210425233509.9ce29da49037e1a421000bdd@xxxxxxxx

Johan