linux-kernel - Re: [GIT PULL 4/4] intel_th: msu: Fix window switching without windows

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Date:   Tue, 17 Dec 2019 13:06:29 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ammy Yi <ammy.yi@...el.com>, stable@...r.kernel.org
Subject: Re: [GIT PULL 4/4] intel_th: msu: Fix window switching without
 windows

On Tue, Dec 17, 2019 at 01:55:27PM +0200, Alexander Shishkin wrote:
> Commit 6cac7866c2741 ("intel_th: msu: Add a sysfs attribute to trigger
> window switch") adds a NULL pointer dereference in the case when there are
> no windows allocated:

Commit ids should only be specified in 12 digits, not 13 :)


> 
> > BUG: kernel NULL pointer dereference, address: 0000000000000000
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > PGD 0 P4D 0
> > Oops: 0000 1 SMP
> > CPU: 5 PID: 1110 Comm: bash Not tainted 5.5.0-rc1+ #1
> > RIP: 0010:msc_win_switch+0xa/0x80 [intel_th_msu]
> > Call Trace:
> > ? win_switch_store+0x9b/0xc0 [intel_th_msu]
> > dev_attr_store+0x17/0x30
> > sysfs_kf_write+0x3e/0x50
> > kernfs_fop_write+0xda/0x1b0
> > __vfs_write+0x1b/0x40
> > vfs_write+0xb9/0x1a0
> > ksys_write+0x67/0xe0
> > __x64_sys_write+0x1a/0x20
> > do_syscall_64+0x57/0x1d0
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Fix that by disallowing window switching with multiwindow buffers without
> windows.
> 
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Fixes: 6cac7866c2741 ("intel_th: msu: Add a sysfs attribute to trigger window switch")

Same here.

I can go edit it by hand...