On Fri, Jul 31, 2020 at 08:57:53AM +0200, Christian König wrote:
Am 31.07.20 um 08:53 schrieb Greg Kroah-Hartman:
On Thu, Jul 30, 2020 at 05:09:07PM -0400, Luben Tuikov wrote:
On 2020-07-29 9:49 a.m., Alex Deucher wrote:
On Wed, Jul 29, 2020 at 4:11 AM Christian König ckoenig.leichtzumerken@gmail.com wrote:
Am 28.07.20 um 21:29 schrieb Peilin Ye:
Compiler leaves a 4-byte hole near the end of `dev_info`, causing amdgpu_info_ioctl() to copy uninitialized kernel stack memory to userspace when `size` is greater than 356.
In 2015 we tried to fix this issue by doing `= {};` on `dev_info`, which unfortunately does not initialize that 4-byte hole. Fix it by using memset() instead.
Cc: stable@vger.kernel.org Fixes: c193fa91b918 ("drm/amdgpu: information leak in amdgpu_info_ioctl()") Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)") Suggested-by: Dan Carpenter dan.carpenter@oracle.com Signed-off-by: Peilin Ye yepeilin.cs@gmail.com
Reviewed-by: Christian König christian.koenig@amd.com
I can't count how many of those we have fixed over the years.
At some point we should probably document that using "= {}" or "= { 0 }" in the kernel is a really bad idea and should be avoided.
Moreover, it seems like different compilers seem to behave relatively differently with these and we often get reports of warnings with these on clang. When in doubt, memset.
There are quite a few of those under drivers/gpu/drm, for "amd/", "scheduler/" drm*.c files,
$find . ( -regex "./drm.*.c" -or -regex "./amd/.*.c" -or -regex "./scheduler/.*.c" ) -exec egrep -n -- " *= *{ *(|NULL|0) *}" {} + | wc -l 374 $_
Out of which only 16 are of the non-ISO C variety, "= {}",
$find . ( -regex "./drm.*.c" -or -regex "./amd/.*.c" -or -regex "./scheduler/.*.c" ) -exec egrep -n -- " *= *{ *}" {} + | wc -l 16 $_
Perhaps the latter are the more pressing ones, since it is a C++ initializer and not a ISO C one.
It only matters when we care copying the data to userspace, if it all stays in the kernel, all is fine.
Well only as long as you don't try to compute a CRC32, MD5 or any fingerprint for a hash from the bytes from the structure.
Then it fails horrible and you wonder why the code doesn't works as expected.
True, but the number of times I have ever needed to do that to a structure for a driver is, um, never...
If a structure ever needs to have that happen to it, I would sure hope the developer was aware of padding fields, otherwise, well, someone needs to take away their C language certification :)
thanks,
greg k-h