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2021-05-02.gitignore: prefix local generated files with a slashMasahiro Yamada1-4/+4
The pattern prefixed with '/' matches files in the same directory, but not ones in sub-directories. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Acked-by: Miguel Ojeda <ojeda@kernel.org> Acked-by: Rob Herring <robh@kernel.org> Acked-by: Andra Paraschiv <andraprs@amazon.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: Gabriel Krisman Bertazi <krisman@collabora.com>
2020-08-10kbuild: introduce hostprogs-always-y and userprogs-always-yMasahiro Yamada1-3/+1
To build host programs, you need to add the program names to 'hostprogs' to use the necessary build rule, but it is not enough to build them because there is no dependency. There are two types of host programs: built as the prerequisite of another (e.g. gen_crc32table in lib/Makefile), or always built when Kbuild visits the Makefile (e.g. genksyms in scripts/genksyms/Makefile). The latter is typical in Makefiles under scripts/, which contains host programs globally used during the kernel build. To build them, you need to add them to both 'hostprogs' and 'always-y'. This commit adds hostprogs-always-y as a shorthand. The same applies to user programs. net/bpfilter/Makefile builds bpfilter_umh on demand, hence always-y is unneeded. In contrast, programs under samples/ are added to both 'userprogs' and 'always-y' so they are always built when Kbuild visits the Makefiles. userprogs-always-y works as a shorthand. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
2020-05-17samples: seccomp: build sample programs for target architectureMasahiro Yamada1-39/+3
These userspace programs include UAPI headers exported to usr/include/. 'make headers' always works for the target architecture (i.e. the same architecture as the kernel), so the sample programs should be built for the target as well. Kbuild now supports 'userprogs' for that. I also guarded the CONFIG option by 'depends on CC_CAN_LINK' because $(CC) may not provide libc. The 'ifndef CROSS_COMPILE' is no longer needed. BTW, the -m31 for s390 is left-over code. Commit 5a79859ae0f3 ("s390: remove 31 bit support") killed it. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Acked-by: Sam Ravnborg <sam@ravnborg.org>
2020-03-25.gitignore: add SPDX License IdentifierMasahiro Yamada1-0/+1
Add SPDX License Identifier to all .gitignore files. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-02-04kbuild: rename hostprogs-y/always to hostprogs/always-yMasahiro Yamada1-2/+2
In old days, the "host-progs" syntax was used for specifying host programs. It was renamed to the current "hostprogs-y" in 2004. It is typically useful in scripts/Makefile because it allows Kbuild to selectively compile host programs based on the kernel configuration. This commit renames like follows: always -> always-y hostprogs-y -> hostprogs So, scripts/Makefile will look like this: always-$(CONFIG_BUILD_BIN2C) += ... always-$(CONFIG_KALLSYMS) += ... ... hostprogs := $(always-y) $(always-m) I think this makes more sense because a host program is always a host program, irrespective of the kernel configuration. We want to specify which ones to compile by CONFIG options, so always-y will be handier. The "always", "hostprogs-y", "hostprogs-m" will be kept for backward compatibility for a while. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
2020-01-02samples/seccomp: Zero out members based on seccomp_notif_sizesSargun Dhillon1-2/+2
The sizes by which seccomp_notif and seccomp_notif_resp are allocated are based on the SECCOMP_GET_NOTIF_SIZES ioctl. This allows for graceful extension of these datastructures. If userspace zeroes out the datastructure based on its version, and it is lagging behind the kernel's version, it will end up sending trailing garbage. On the other hand, if it is ahead of the kernel version, it will write extra zero space, and potentially cause corruption. Signed-off-by: Sargun Dhillon <sargun@sargun.me> Suggested-by: Tycho Andersen <tycho@tycho.ws> Link: https://lore.kernel.org/r/20191230203503.4925-1-sargun@sargun.me Fixes: fec7b6690541 ("samples: add an example of seccomp user trap") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org>
2019-05-18samples: guard sub-directories with CONFIG optionsMasahiro Yamada1-1/+1
Do not descend to sub-directories when unneeded. I used subdir-$(CONFIG_...) for hidraw, seccomp, and vfs because they only contain host programs. While we are here, let's add SPDX License tag, and sort the directories alphabetically. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2019-05-03samples: seccomp: turn CONFIG_SAMPLE_SECCOMP into a bool optionMasahiro Yamada1-1/+1
The prompt of CONFIG_SAMPLE_SECCOMP claims this is "loadable module only", which is invalid. samples/seccomp/ only contains host programs, so having it tristate is pointless. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2019-01-08samples/seccomp: Fix 32-bit buildTycho Andersen1-0/+1
Both the .o and the actual executable need to be built with -m32 in order to link correctly. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Tycho Andersen <tycho@tycho.ws> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Borislav Petkov <bp@alien8.de> Cc: James Morris <jmorris@namei.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: fec7b6690541 ("samples: add an example of seccomp user trap") Link: http://lkml.kernel.org/r/20190107231631.1849-1-tycho@tycho.ws Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-12-11samples: add an example of seccomp user trapTycho Andersen3-1/+382
The idea here is just to give a demonstration of how one could safely use the SECCOMP_RET_USER_NOTIF feature to do mount policies. This particular policy is (as noted in the comment) not very interesting, but it serves to illustrate how one might apply a policy dodging the various TOCTOU issues. Signed-off-by: Tycho Andersen <tycho@tycho.ws> CC: Kees Cook <keescook@chromium.org> CC: Andy Lutomirski <luto@amacapital.net> CC: Oleg Nesterov <oleg@redhat.com> CC: Eric W. Biederman <ebiederm@xmission.com> CC: "Serge E. Hallyn" <serge@hallyn.com> CC: Christian Brauner <christian@brauner.io> CC: Tyler Hicks <tyhicks@canonical.com> CC: Akihiro Suda <suda.akihiro@lab.ntt.co.jp> Signed-off-by: Kees Cook <keescook@chromium.org>
2018-07-18kbuild: Rename HOST_LOADLIBES to KBUILD_HOSTLDLIBSLaura Abbott1-3/+3
In preparation for enabling command line LDLIBS, re-name HOST_LOADLIBES to KBUILD_HOSTLDLIBS as the internal use only flags. Also rename existing usage to HOSTLDLIBS for consistency. This should not have any visible effects. Signed-off-by: Laura Abbott <labbott@redhat.com> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2018-02-22samples/seccomp: do not compile when cross compiledMichal Hocko1-9/+1
samples/seccomp relies on the host setting which is not suitable for crosscompilation and it actually fails when crosscompiling s390 and powerpc all{yes,mod}config on x86_64 with samples/seccomp/bpf-helper.h:135:2: error: #error __BITS_PER_LONG value unusable. #error __BITS_PER_LONG value unusable. ^ In file included from samples/seccomp/bpf-fancy.c:13:0: samples/seccomp/bpf-fancy.c: In function ‘main’: samples/seccomp/bpf-fancy.c:38:11: error: ‘__NR_exit’ undeclared (first use in this function) SYSCALL(__NR_exit, ALLOW), and many others. I am doing these for compile testing and it's been quite useful to catch issues. Crosscompiling sample code on the other hand doesn't seem all that important so it seems like the easiest way to simply disable samples/seccomp when crosscompiling. Fixing this properly is not that easy as Kees explains: : IIRC, one of the problems is with build ordering problems: the kernel : headers used by the samples aren't available when cross compiling. Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Kees Cook <keescook@chromium.org>
2017-11-18kbuild: remove all dummy assignments to obj-Masahiro Yamada1-3/+0
Now kbuild core scripts create empty built-in.o where necessary. Remove "obj- := dummy.o" tricks. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2017-11-02License cleanup: add SPDX GPL-2.0 license identifier to files with no licenseGreg Kroah-Hartman6-0/+6
Many source files in the tree are missing licensing information, which makes it harder for compliance tools to determine the correct license. By default all files without license information are under the default license of the kernel, which is GPL version 2. Update the files which contain no license information with the 'GPL-2.0' SPDX license identifier. The SPDX identifier is a legally binding shorthand, which can be used instead of the full boiler plate text. This patch is based on work done by Thomas Gleixner and Kate Stewart and Philippe Ombredanne. How this work was done: Patches were generated and checked against linux-4.14-rc6 for a subset of the use cases: - file had no licensing information it it. - file was a */uapi/* one with no licensing information in it, - file was a */uapi/* one with existing licensing information, Further patches will be generated in subsequent months to fix up cases where non-standard license headers were used, and references to license had to be inferred by heuristics based on keywords. The analysis to determine which SPDX License Identifier to be applied to a file was done in a spreadsheet of side by side results from of the output of two independent scanners (ScanCode & Windriver) producing SPDX tag:value files created by Philippe Ombredanne. Philippe prepared the base worksheet, and did an initial spot review of a few 1000 files. The 4.13 kernel was the starting point of the analysis with 60,537 files assessed. Kate Stewart did a file by file comparison of the scanner results in the spreadsheet to determine which SPDX license identifier(s) to be applied to the file. She confirmed any determination that was not immediately clear with lawyers working with the Linux Foundation. Criteria used to select files for SPDX license identifier tagging was: - Files considered eligible had to be source code files. - Make and config files were included as candidates if they contained >5 lines of source - File already had some variant of a license header in it (even if <5 lines). All documentation files were explicitly excluded. The following heuristics were used to determine which SPDX license identifiers to apply. - when both scanners couldn't find any license traces, file was considered to have no license information in it, and the top level COPYING file license applied. For non */uapi/* files that summary was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 11139 and resulted in the first patch in this series. If that file was a */uapi/* path one, it was "GPL-2.0 WITH Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 WITH Linux-syscall-note 930 and resulted in the second patch in this series. - if a file had some form of licensing information in it, and was one of the */uapi/* ones, it was denoted with the Linux-syscall-note if any GPL family license was found in the file or had no licensing in it (per prior point). Results summary: SPDX license identifier # files ---------------------------------------------------|------ GPL-2.0 WITH Linux-syscall-note 270 GPL-2.0+ WITH Linux-syscall-note 169 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17 LGPL-2.1+ WITH Linux-syscall-note 15 GPL-1.0+ WITH Linux-syscall-note 14 ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5 LGPL-2.0+ WITH Linux-syscall-note 4 LGPL-2.1 WITH Linux-syscall-note 3 ((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3 ((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1 and that resulted in the third patch in this series. - when the two scanners agreed on the detected license(s), that became the concluded license(s). - when there was disagreement between the two scanners (one detected a license but the other didn't, or they both detected different licenses) a manual inspection of the file occurred. - In most cases a manual inspection of the information in the file resulted in a clear resolution of the license that should apply (and which scanner probably needed to revisit its heuristics). - When it was not immediately clear, the license identifier was confirmed with lawyers working with the Linux Foundation. - If there was any question as to the appropriate license identifier, the file was flagged for further research and to be revisited later in time. In total, over 70 hours of logged manual review was done on the spreadsheet to determine the SPDX license identifiers to apply to the source files by Kate, Philippe, Thomas and, in some cases, confirmation by lawyers working with the Linux Foundation. Kate also obtained a third independent scan of the 4.13 code base from FOSSology, and compared selected files where the other two scanners disagreed against that SPDX file, to see if there was new insights. The Windriver scanner is based on an older version of FOSSology in part, so they are related. Thomas did random spot checks in about 500 files from the spreadsheets for the uapi headers and agreed with SPDX license identifier in the files he inspected. For the non-uapi files Thomas did random spot checks in about 15000 files. In initial set of patches against 4.14-rc6, 3 files were found to have copy/paste license identifier errors, and have been fixed to reflect the correct identifier. Additionally Philippe spent 10 hours this week doing a detailed manual inspection and review of the 12,461 patched files from the initial patch version early this week with: - a full scancode scan run, collecting the matched texts, detected license ids and scores - reviewing anything where there was a license detected (about 500+ files) to ensure that the applied SPDX license was correct - reviewing anything where there was no detection but the patch license was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied SPDX license was correct This produced a worksheet with 20 files needing minor correction. This worksheet was then exported into 3 different .csv files for the different types of files to be modified. These .csv files were then reviewed by Greg. Thomas wrote a script to parse the csv files and add the proper SPDX tag to the file, in the format that the file expected. This script was further refined by Greg based on the output to detect more types of files automatically and to distinguish between header and source .c files (which need different comment types.) Finally Greg ran the script using the .csv files to generate the patches. Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-01-09samples/seccomp: fix 64-bit comparison macrosMathias Svensson1-53/+72
There were some bugs in the JNE64 and JLT64 comparision macros. This fixes them, improves comments, and cleans up the file while we are at it. Reported-by: Stephen Röttger <sroettger@google.com> Signed-off-by: Mathias Svensson <idolf@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> Cc: stable@vger.kernel.org Signed-off-by: James Morris <james.l.morris@oracle.com>
2016-11-01samples/seccomp: Support programs with >256 instructionsRicky Zhou1-19/+19
Previously, the program size was incorrectly truncated to 8 bits, resulting in broken labels in large programs. Also changes the jump resolution loop to not rely on undefined behavior (making a pointer point before the filter array). Signed-off-by: Ricky Zhou <rickyz@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org>
2016-11-01samples/seccomp: Enable PR_SET_NO_NEW_PRIVS in dropperRicky Zhou1-2/+5
Either CAP_SYS_ADMIN or PR_SET_NO_NEW_PRIVS is required to enable seccomp. This allows samples/seccomp/dropper to be run without CAP_SYS_ADMIN. Signed-off-by: Ricky Zhou <rickyz@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org>
2016-11-01samples/seccomp: Fix hostprogs variableRicky Zhou1-2/+2
In f6041c1d, a separate SAMPLES_SECCOMP option was added. This changed hostprogs-y to hostprogs-m, so adjust it. Signed-off-by: Ricky Zhou <rickyz@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org>
2016-07-07samples/seccomp: Add standalone config optionOlof Johansson1-1/+1
Add a separate Kconfig option for SAMPLES_SECCOMP. Main reason for this is that, just like other samples, it's forced to be a module. Without this, since the sample is a target only controlled by CONFIG_SECCOMP_FILTER, the samples will be built before include files are put in place properly. For example, from an arm64 allmodconfig built with "make -sk -j 32" (without specific target), the following happens: samples/seccomp/bpf-fancy.c:13:27: fatal error: linux/seccomp.h: No such file or directory samples/seccomp/bpf-helper.h:20:50: fatal error: linux/seccomp.h: No such file or directory samples/seccomp/dropper.c:20:27: fatal error: linux/seccomp.h: No such file or directory samples/seccomp/bpf-direct.c:21:27: fatal error: linux/seccomp.h: No such file or directory So, just stick to the same format as other samples. Signed-off-by: Olof Johansson <olof@lixom.net> Signed-off-by: Kees Cook <keescook@chromium.org>
2015-02-17samples/seccomp: improve label helperKees Cook2-1/+9
Fixes a potential corruption with uninitialized stack memory in the seccomp BPF sample program. [akpm@linux-foundation.org: coding-style fixlet] Signed-off-by: Kees Cook <keescook@chromium.org> Reported-by: Robert Swiecki <swiecki@google.com> Tested-by: Robert Swiecki <swiecki@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-04-03samples/seccomp/Makefile: do not build tests if cross-compiling for MIPSMarkos Chandras1-4/+10
The Makefile is designed to use the host toolchain so it may be unsafe to build the tests if the kernel has been configured and built for another architecture. This fixes a build problem when the kernel has been configured and built for the MIPS architecture but the host is not MIPS (cross-compiled). The MIPS syscalls are only defined if one of the following is true: 1) _MIPS_SIM == _MIPS_SIM_ABI64 2) _MIPS_SIM == _MIPS_SIM_ABI32 3) _MIPS_SIM == _MIPS_SIM_NABI32 Of course, none of these make sense on a non-MIPS toolchain and the following build problem occurs when building on a non-MIPS host. linux/usr/include/linux/kexec.h:50: userspace cannot reference function or variable defined in the kernel samples/seccomp/bpf-direct.c: In function `emulator': samples/seccomp/bpf-direct.c:76:17: error: `__NR_write' undeclared (first use in this function) Signed-off-by: Markos Chandras <markos.chandras@imgtec.com> Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-02-05samples/seccomp: be less stupid about cross compilingArnd Bergmann1-0/+2
The seccomp filters are currently built for the build host, not for the machine that they are going to run on, but they are also built for with the -m32 flag if the kernel is built for a 32 bit machine, both of which seems rather odd. It broke allyesconfig on my machine, which is x86-64, but building for 32 bit ARM, with this error message: In file included from /usr/include/stdio.h:28:0, from samples/seccomp/bpf-fancy.c:15: /usr/include/features.h:324:26: fatal error: bits/predefs.h: No such file or directory because there are no 32 bit libc headers installed on this machine. We should really be building all the samples for the target machine rather than the build host, but since the infrastructure for that appears to be missing right now, let's be a little bit smarter and not pass the '-m32' flag to the HOSTCC when cross- compiling. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Kees Cook <keescook@chromium.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: James Morris <james.l.morris@oracle.com> Acked-by: Will Drewry <wad@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-09-12samples/seccomp: fix 31 bit build on s390Heiko Carstens1-8/+16
On s390 the flag to force 31 builds is -m31 instead of -m32 unlike on all (?) other architectures. Fixes this compile error: HOSTCC samples/seccomp/bpf-direct.o cc1: error: unrecognized command line option "-m32" make[2]: *** [samples/seccomp/bpf-direct.o] Error 1 Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
2012-08-03samples/seccomp: fix endianness bug in LO_ARG defineHeiko Carstens1-5/+10
The LO_ARG define needs to consider endianness also for 32 bit builds. The "bpf_fancy" test case didn't work on s390 in 32 bit and compat mode because the LO_ARG define resulted in a BPF program which read the upper halve of the 64 bit system call arguments instead of the lower halves. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
2012-06-29samples: seccomp: add .gitignore for untracked executablesChad Williamson1-0/+3
git status should be clean following make allmodconfig && make. Add a .gitignore file to the samples/seccomp directory to ignore binaries produced there. Signed-off-by: Chad Williamson <chad@dahc.us> Reviewed-By: Will Drewry <wad@chromium.org> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
2012-04-19samples/seccomp: fix dependencies on arch macrosWill Drewry2-11/+19
This change fixes the compilation error triggered here for i386 allmodconfig in linux-next: http://kisskb.ellerman.id.au/kisskb/buildresult/6123842/ Logic attempting to predict the host architecture has been removed from the Makefile. Instead, the bpf-direct sample should now compile on any architecture, but if the architecture is not supported, it will compile a minimal main() function. This change also ensures the samples are not compiled when there is no seccomp filter support. (Note, I wasn't able to reproduce the error locally, but the existing approach was clearly flawed. This tweak should resolve your issue and avoid other future weirdness.) Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com> Suggested-by: Kees Cook <keescook@chromium.org> Signed-off-by: Will Drewry <wad@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
2012-04-14Documentation: prctl/seccomp_filterWill Drewry6-0/+711
Documents how system call filtering using Berkeley Packet Filter programs works and how it may be used. Includes an example for x86 and a semi-generic example using a macro-based code generator. Acked-by: Eric Paris <eparis@redhat.com> Signed-off-by: Will Drewry <wad@chromium.org> Acked-by: Kees Cook <keescook@chromium.org> v18: - added acked by - update no new privs numbers v17: - remove @compat note and add Pitfalls section for arch checking (keescook@chromium.org) v16: - v15: - v14: - rebase/nochanges v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc v12: - comment on the ptrace_event use - update arch support comment - note the behavior of SECCOMP_RET_DATA when there are multiple filters (keescook@chromium.org) - lots of samples/ clean up incl 64-bit bpf-direct support (markus@chromium.org) - rebase to linux-next v11: - overhaul return value language, updates (keescook@chromium.org) - comment on do_exit(SIGSYS) v10: - update for SIGSYS - update for new seccomp_data layout - update for ptrace option use v9: - updated bpf-direct.c for SIGILL v8: - add PR_SET_NO_NEW_PRIVS to the samples. v7: - updated for all the new stuff in v7: TRAP, TRACE - only talk about PR_SET_SECCOMP now - fixed bad JLE32 check (coreyb@linux.vnet.ibm.com) - adds dropper.c: a simple system call disabler v6: - tweak the language to note the requirement of PR_SET_NO_NEW_PRIVS being called prior to use. (luto@mit.edu) v5: - update sample to use system call arguments - adds a "fancy" example using a macro-based generator - cleaned up bpf in the sample - update docs to mention arguments - fix prctl value (eparis@redhat.com) - language cleanup (rdunlap@xenotime.net) v4: - update for no_new_privs use - minor tweaks v3: - call out BPF <-> Berkeley Packet Filter (rdunlap@xenotime.net) - document use of tentative always-unprivileged - guard sample compilation for i386 and x86_64 v2: - move code to samples (corbet@lwn.net) Signed-off-by: James Morris <james.l.morris@oracle.com>