diff options
Diffstat (limited to 'Documentation/process')
| -rw-r--r-- | Documentation/process/2.Process.rst | 2 | ||||
| -rw-r--r-- | Documentation/process/adding-syscalls.rst | 2 | ||||
| -rw-r--r-- | Documentation/process/deprecated.rst | 119 | ||||
| -rw-r--r-- | Documentation/process/howto.rst | 13 | ||||
| -rw-r--r-- | Documentation/process/index.rst | 2 | ||||
| -rw-r--r-- | Documentation/process/license-rules.rst | 2 |
6 files changed, 132 insertions, 8 deletions
diff --git a/Documentation/process/2.Process.rst b/Documentation/process/2.Process.rst index 51d0349c7809..ae020d84d7c4 100644 --- a/Documentation/process/2.Process.rst +++ b/Documentation/process/2.Process.rst @@ -82,7 +82,7 @@ As an example, here is how the 4.16 development cycle went (all dates in March 11 4.16-rc5 March 18 4.16-rc6 March 25 4.16-rc7 - April 1 4.17 stable release + April 1 4.16 stable release ============== =============================== How do the developers decide when to close the development cycle and create diff --git a/Documentation/process/adding-syscalls.rst b/Documentation/process/adding-syscalls.rst index 0d4f29bc798b..88a7d5c8bb2f 100644 --- a/Documentation/process/adding-syscalls.rst +++ b/Documentation/process/adding-syscalls.rst @@ -232,7 +232,7 @@ normally be optional, so add a ``CONFIG`` option (typically to by the option. - Make the option depend on EXPERT if it should be hidden from normal users. - Make any new source files implementing the function dependent on the CONFIG - option in the Makefile (e.g. ``obj-$(CONFIG_XYZZY_SYSCALL) += xyzzy.c``). + option in the Makefile (e.g. ``obj-$(CONFIG_XYZZY_SYSCALL) += xyzzy.o``). - Double check that the kernel still builds with the new CONFIG option turned off. diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst new file mode 100644 index 000000000000..0ef5a63c06ba --- /dev/null +++ b/Documentation/process/deprecated.rst @@ -0,0 +1,119 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================================================================== +Deprecated Interfaces, Language Features, Attributes, and Conventions +===================================================================== + +In a perfect world, it would be possible to convert all instances of +some deprecated API into the new API and entirely remove the old API in +a single development cycle. However, due to the size of the kernel, the +maintainership hierarchy, and timing, it's not always feasible to do these +kinds of conversions at once. This means that new instances may sneak into +the kernel while old ones are being removed, only making the amount of +work to remove the API grow. In order to educate developers about what +has been deprecated and why, this list has been created as a place to +point when uses of deprecated things are proposed for inclusion in the +kernel. + +__deprecated +------------ +While this attribute does visually mark an interface as deprecated, +it `does not produce warnings during builds any more +<https://git.kernel.org/linus/771c035372a036f83353eef46dbb829780330234>`_ +because one of the standing goals of the kernel is to build without +warnings and no one was actually doing anything to remove these deprecated +interfaces. While using `__deprecated` is nice to note an old API in +a header file, it isn't the full solution. Such interfaces must either +be fully removed from the kernel, or added to this file to discourage +others from using them in the future. + +open-coded arithmetic in allocator arguments +-------------------------------------------- +Dynamic size calculations (especially multiplication) should not be +performed in memory allocator (or similar) function arguments due to the +risk of them overflowing. This could lead to values wrapping around and a +smaller allocation being made than the caller was expecting. Using those +allocations could lead to linear overflows of heap memory and other +misbehaviors. (One exception to this is literal values where the compiler +can warn if they might overflow. Though using literals for arguments as +suggested below is also harmless.) + +For example, do not use ``count * size`` as an argument, as in:: + + foo = kmalloc(count * size, GFP_KERNEL); + +Instead, the 2-factor form of the allocator should be used:: + + foo = kmalloc_array(count, size, GFP_KERNEL); + +If no 2-factor form is available, the saturate-on-overflow helpers should +be used:: + + bar = vmalloc(array_size(count, size)); + +Another common case to avoid is calculating the size of a structure with +a trailing array of others structures, as in:: + + header = kzalloc(sizeof(*header) + count * sizeof(*header->item), + GFP_KERNEL); + +Instead, use the helper:: + + header = kzalloc(struct_size(header, item, count), GFP_KERNEL); + +See :c:func:`array_size`, :c:func:`array3_size`, and :c:func:`struct_size`, +for more details as well as the related :c:func:`check_add_overflow` and +:c:func:`check_mul_overflow` family of functions. + +simple_strtol(), simple_strtoll(), simple_strtoul(), simple_strtoull() +---------------------------------------------------------------------- +The :c:func:`simple_strtol`, :c:func:`simple_strtoll`, +:c:func:`simple_strtoul`, and :c:func:`simple_strtoull` functions +explicitly ignore overflows, which may lead to unexpected results +in callers. The respective :c:func:`kstrtol`, :c:func:`kstrtoll`, +:c:func:`kstrtoul`, and :c:func:`kstrtoull` functions tend to be the +correct replacements, though note that those require the string to be +NUL or newline terminated. + +strcpy() +-------- +:c:func:`strcpy` performs no bounds checking on the destination +buffer. This could result in linear overflows beyond the +end of the buffer, leading to all kinds of misbehaviors. While +`CONFIG_FORTIFY_SOURCE=y` and various compiler flags help reduce the +risk of using this function, there is no good reason to add new uses of +this function. The safe replacement is :c:func:`strscpy`. + +strncpy() on NUL-terminated strings +----------------------------------- +Use of :c:func:`strncpy` does not guarantee that the destination buffer +will be NUL terminated. This can lead to various linear read overflows +and other misbehavior due to the missing termination. It also NUL-pads the +destination buffer if the source contents are shorter than the destination +buffer size, which may be a needless performance penalty for callers using +only NUL-terminated strings. The safe replacement is :c:func:`strscpy`. +(Users of :c:func:`strscpy` still needing NUL-padding will need an +explicit :c:func:`memset` added.) + +If a caller is using non-NUL-terminated strings, :c:func:`strncpy()` can +still be used, but destinations should be marked with the `__nonstring +<https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html>`_ +attribute to avoid future compiler warnings. + +strlcpy() +--------- +:c:func:`strlcpy` reads the entire source buffer first, possibly exceeding +the given limit of bytes to copy. This is inefficient and can lead to +linear read overflows if a source string is not NUL-terminated. The +safe replacement is :c:func:`strscpy`. + +Variable Length Arrays (VLAs) +----------------------------- +Using stack VLAs produces much worse machine code than statically +sized stack arrays. While these non-trivial `performance issues +<https://git.kernel.org/linus/02361bc77888>`_ are reason enough to +eliminate VLAs, they are also a security risk. Dynamic growth of a stack +array may exceed the remaining memory in the stack segment. This could +lead to a crash, possible overwriting sensitive contents at the end of the +stack (when built without `CONFIG_THREAD_INFO_IN_TASK=y`), or overwriting +memory adjacent to the stack (when built without `CONFIG_VMAP_STACK=y`) diff --git a/Documentation/process/howto.rst b/Documentation/process/howto.rst index 130bf0f48875..dcb25f94188e 100644 --- a/Documentation/process/howto.rst +++ b/Documentation/process/howto.rst @@ -57,12 +57,13 @@ of doing things. Legal Issues ------------ -The Linux kernel source code is released under the GPL. Please see the -file, COPYING, in the main directory of the source tree, for details on -the license. If you have further questions about the license, please -contact a lawyer, and do not ask on the Linux kernel mailing list. The -people on the mailing lists are not lawyers, and you should not rely on -their statements on legal matters. +The Linux kernel source code is released under the GPL. Please see the file +COPYING in the main directory of the source tree. The Linux kernel licensing +rules and how to use `SPDX <https://spdx.org/>`_ identifiers in source code are +descibed in :ref:`Documentation/process/license-rules.rst <kernel_licensing>`. +If you have further questions about the license, please contact a lawyer, and do +not ask on the Linux kernel mailing list. The people on the mailing lists are +not lawyers, and you should not rely on their statements on legal matters. For common questions and answers about the GPL, please see: diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst index 42691e2880eb..757808526d9a 100644 --- a/Documentation/process/index.rst +++ b/Documentation/process/index.rst @@ -19,6 +19,7 @@ Below are the essential guides that every developer should read. .. toctree:: :maxdepth: 1 + license-rules howto code-of-conduct code-of-conduct-interpretation @@ -42,6 +43,7 @@ Other guides to the community that are of interest to most developers are: stable-kernel-rules submit-checklist kernel-docs + deprecated These are some overall technical guides that have been put here for now for lack of a better place. diff --git a/Documentation/process/license-rules.rst b/Documentation/process/license-rules.rst index 8ea26325fe3f..2bb8c0fc2238 100644 --- a/Documentation/process/license-rules.rst +++ b/Documentation/process/license-rules.rst @@ -1,5 +1,7 @@ .. SPDX-License-Identifier: GPL-2.0 +.. _kernel_licensing: + Linux kernel licensing rules ============================ |