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Commit6cac7866c2("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: > 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@linux.intel.com> Fixes:6cac7866c2("intel_th: msu: Add a sysfs attribute to trigger window switch") Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reported-by: Ammy Yi <ammy.yi@intel.com> Tested-by: Ammy Yi <ammy.yi@intel.com> Cc: stable@vger.kernel.org # v5.2+ Link: https://lore.kernel.org/r/20191217115527.74383-5-alexander.shishkin@linux.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.