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authorDaniel Mentz <danielmentz@google.com>2017-07-19 19:03:19 -0400
committerMauro Carvalho Chehab <mchehab@s-opensource.com>2018-01-30 07:40:41 -0500
commita1dfb4c48cc1e64eeb7800a27c66a6f7e88d075a (patch)
tree82a9215c0a4862a44dd023f7381584efdf8ee504 /Documentation/devicetree/bindings/display/panel/toppoly,td028ttec1.txt
parentd83a8243aaefe62ace433e4384a4f077bed86acb (diff)
media: v4l2-compat-ioctl32.c: refactor compat ioctl32 logic
The 32-bit compat v4l2 ioctl handling is implemented based on its 64-bit equivalent. It converts 32-bit data structures into its 64-bit equivalents and needs to provide the data to the 64-bit ioctl in user space memory which is commonly allocated using compat_alloc_user_space(). However, due to how that function is implemented, it can only be called a single time for every syscall invocation. Supposedly to avoid this limitation, the existing code uses a mix of memory from the kernel stack and memory allocated through compat_alloc_user_space(). Under normal circumstances, this would not work, because the 64-bit ioctl expects all pointers to point to user space memory. As a workaround, set_fs(KERNEL_DS) is called to temporarily disable this extra safety check and allow kernel pointers. However, this might introduce a security vulnerability: The result of the 32-bit to 64-bit conversion is writeable by user space because the output buffer has been allocated via compat_alloc_user_space(). A malicious user space process could then manipulate pointers inside this output buffer, and due to the previous set_fs(KERNEL_DS) call, functions like get_user() or put_user() no longer prevent kernel memory access. The new approach is to pre-calculate the total amount of user space memory that is needed, allocate it using compat_alloc_user_space() and then divide up the allocated memory to accommodate all data structures that need to be converted. An alternative approach would have been to retain the union type karg that they allocated on the kernel stack in do_video_ioctl(), copy all data from user space into karg and then back to user space. However, we decided against this approach because it does not align with other compat syscall implementations. Instead, we tried to replicate the get_user/put_user pairs as found in other places in the kernel: if (get_user(clipcount, &up->clipcount) || put_user(clipcount, &kp->clipcount)) return -EFAULT; Notes from hans.verkuil@cisco.com: This patch was taken from: https://github.com/LineageOS/android_kernel_samsung_apq8084/commit/97b733953c06e4f0398ade18850f0817778255f7 Clearly nobody could be bothered to upstream this patch or at minimum tell us :-( We only heard about this a week ago. This patch was rebased and cleaned up. Compared to the original I also swapped the order of the convert_in_user arguments so that they matched copy_in_user. It was hard to review otherwise. I also replaced the ALLOC_USER_SPACE/ALLOC_AND_GET by a normal function. Fixes: 6b5a9492ca ("v4l: introduce string control support.") Signed-off-by: Daniel Mentz <danielmentz@google.com> Co-developed-by: Hans Verkuil <hans.verkuil@cisco.com> Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Cc: <stable@vger.kernel.org> # for v4.15 and up Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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