From 50d7bd38c3aafc4749e05e8d7fcb616979143602 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 17 May 2021 20:01:15 -0700 Subject: stddef: Introduce struct_group() helper macro Kernel code has a regular need to describe groups of members within a structure usually when they need to be copied or initialized separately from the rest of the surrounding structure. The generally accepted design pattern in C is to use a named sub-struct: struct foo { int one; struct { int two; int three, four; } thing; int five; }; This would allow for traditional references and sizing: memcpy(&dst.thing, &src.thing, sizeof(dst.thing)); However, doing this would mean that referencing struct members enclosed by such named structs would always require including the sub-struct name in identifiers: do_something(dst.thing.three); This has tended to be quite inflexible, especially when such groupings need to be added to established code which causes huge naming churn. Three workarounds exist in the kernel for this problem, and each have other negative properties. To avoid the naming churn, there is a design pattern of adding macro aliases for the named struct: #define f_three thing.three This ends up polluting the global namespace, and makes it difficult to search for identifiers. Another common work-around in kernel code avoids the pollution by avoiding the named struct entirely, instead identifying the group's boundaries using either a pair of empty anonymous structs of a pair of zero-element arrays: struct foo { int one; struct { } start; int two; int three, four; struct { } finish; int five; }; struct foo { int one; int start[0]; int two; int three, four; int finish[0]; int five; }; This allows code to avoid needing to use a sub-struct named for member references within the surrounding structure, but loses the benefits of being able to actually use such a struct, making it rather fragile. Using these requires open-coded calculation of sizes and offsets. The efforts made to avoid common mistakes include lots of comments, or adding various BUILD_BUG_ON()s. Such code is left with no way for the compiler to reason about the boundaries (e.g. the "start" object looks like it's 0 bytes in length), making bounds checking depend on open-coded calculations: if (length > offsetof(struct foo, finish) - offsetof(struct foo, start)) return -EINVAL; memcpy(&dst.start, &src.start, offsetof(struct foo, finish) - offsetof(struct foo, start)); However, the vast majority of places in the kernel that operate on groups of members do so without any identification of the grouping, relying either on comments or implicit knowledge of the struct contents, which is even harder for the compiler to reason about, and results in even more fragile manual sizing, usually depending on member locations outside of the region (e.g. to copy "two" and "three", use the start of "four" to find the size): BUILD_BUG_ON((offsetof(struct foo, four) < offsetof(struct foo, two)) || (offsetof(struct foo, four) < offsetof(struct foo, three)); if (length > offsetof(struct foo, four) - offsetof(struct foo, two)) return -EINVAL; memcpy(&dst.two, &src.two, length); In order to have a regular programmatic way to describe a struct region that can be used for references and sizing, can be examined for bounds checking, avoids forcing the use of intermediate identifiers, and avoids polluting the global namespace, introduce the struct_group() macro. This macro wraps the member declarations to create an anonymous union of an anonymous struct (no intermediate name) and a named struct (for references and sizing): struct foo { int one; struct_group(thing, int two; int three, four; ); int five; }; if (length > sizeof(src.thing)) return -EINVAL; memcpy(&dst.thing, &src.thing, length); do_something(dst.three); There are some rare cases where the resulting struct_group() needs attributes added, so struct_group_attr() is also introduced to allow for specifying struct attributes (e.g. __align(x) or __packed). Additionally, there are places where such declarations would like to have the struct be tagged, so struct_group_tagged() is added. Given there is a need for a handful of UAPI uses too, the underlying __struct_group() macro has been defined in UAPI so it can be used there too. To avoid confusing scripts/kernel-doc, hide the macro from its struct parsing. Co-developed-by: Keith Packard Signed-off-by: Keith Packard Acked-by: Gustavo A. R. Silva Link: https://lore.kernel.org/lkml/20210728023217.GC35706@embeddedor Enhanced-by: Rasmus Villemoes Link: https://lore.kernel.org/lkml/41183a98-bdb9-4ad6-7eab-5a7292a6df84@rasmusvillemoes.dk Enhanced-by: Dan Williams Link: https://lore.kernel.org/lkml/1d9a2e6df2a9a35b2cdd50a9a68cac5991e7e5f0.camel@intel.com Enhanced-by: Daniel Vetter Link: https://lore.kernel.org/lkml/YQKa76A6XuFqgM03@phenom.ffwll.local Acked-by: Dan Williams Signed-off-by: Kees Cook --- scripts/kernel-doc | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'scripts') diff --git a/scripts/kernel-doc b/scripts/kernel-doc index cfcb60737957..38aa799a776c 100755 --- a/scripts/kernel-doc +++ b/scripts/kernel-doc @@ -1245,6 +1245,13 @@ sub dump_struct($$) { $members =~ s/\s*CRYPTO_MINALIGN_ATTR/ /gos; $members =~ s/\s*____cacheline_aligned_in_smp/ /gos; $members =~ s/\s*____cacheline_aligned/ /gos; + # unwrap struct_group(): + # - first eat non-declaration parameters and rewrite for final match + # - then remove macro, outer parens, and trailing semicolon + $members =~ s/\bstruct_group\s*\(([^,]*,)/STRUCT_GROUP(/gos; + $members =~ s/\bstruct_group_(attr|tagged)\s*\(([^,]*,){2}/STRUCT_GROUP(/gos; + $members =~ s/\b__struct_group\s*\(([^,]*,){3}/STRUCT_GROUP(/gos; + $members =~ s/\bSTRUCT_GROUP(\(((?:(?>[^)(]+)|(?1))*)\))[^;]*;/$2/gos; my $args = qr{([^,)]+)}; # replace DECLARE_BITMAP -- cgit v1.2.3 From be58f7103700a68d5c7ca60a2bc0b309907599ab Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 20 Apr 2021 23:22:52 -0700 Subject: fortify: Add compile-time FORTIFY_SOURCE tests While the run-time testing of FORTIFY_SOURCE is already present in LKDTM, there is no testing of the expected compile-time detections. In preparation for correctly supporting FORTIFY_SOURCE under Clang, adding additional FORTIFY_SOURCE defenses, and making sure FORTIFY_SOURCE doesn't silently regress with GCC, introduce a build-time test suite that checks each expected compile-time failure condition. As this is relatively backwards from standard build rules in the sense that a successful test is actually a compile _failure_, create a wrapper script to check for the correct errors, and wire it up as a dummy dependency to lib/string.o, collecting the results into a log file artifact. Signed-off-by: Kees Cook --- MAINTAINERS | 9 ++++ lib/.gitignore | 2 + lib/Makefile | 33 ++++++++++++++ lib/test_fortify/read_overflow-memchr.c | 5 +++ lib/test_fortify/read_overflow-memchr_inv.c | 5 +++ lib/test_fortify/read_overflow-memcmp.c | 5 +++ lib/test_fortify/read_overflow-memscan.c | 5 +++ lib/test_fortify/read_overflow2-memcmp.c | 5 +++ lib/test_fortify/read_overflow2-memcpy.c | 5 +++ lib/test_fortify/read_overflow2-memmove.c | 5 +++ lib/test_fortify/test_fortify.h | 35 +++++++++++++++ lib/test_fortify/write_overflow-memcpy.c | 5 +++ lib/test_fortify/write_overflow-memmove.c | 5 +++ lib/test_fortify/write_overflow-memset.c | 5 +++ lib/test_fortify/write_overflow-strcpy-lit.c | 5 +++ lib/test_fortify/write_overflow-strcpy.c | 5 +++ lib/test_fortify/write_overflow-strlcpy-src.c | 5 +++ lib/test_fortify/write_overflow-strlcpy.c | 5 +++ lib/test_fortify/write_overflow-strncpy-src.c | 5 +++ lib/test_fortify/write_overflow-strncpy.c | 5 +++ lib/test_fortify/write_overflow-strscpy.c | 5 +++ scripts/test_fortify.sh | 62 +++++++++++++++++++++++++++ 22 files changed, 226 insertions(+) create mode 100644 lib/test_fortify/read_overflow-memchr.c create mode 100644 lib/test_fortify/read_overflow-memchr_inv.c create mode 100644 lib/test_fortify/read_overflow-memcmp.c create mode 100644 lib/test_fortify/read_overflow-memscan.c create mode 100644 lib/test_fortify/read_overflow2-memcmp.c create mode 100644 lib/test_fortify/read_overflow2-memcpy.c create mode 100644 lib/test_fortify/read_overflow2-memmove.c create mode 100644 lib/test_fortify/test_fortify.h create mode 100644 lib/test_fortify/write_overflow-memcpy.c create mode 100644 lib/test_fortify/write_overflow-memmove.c create mode 100644 lib/test_fortify/write_overflow-memset.c create mode 100644 lib/test_fortify/write_overflow-strcpy-lit.c create mode 100644 lib/test_fortify/write_overflow-strcpy.c create mode 100644 lib/test_fortify/write_overflow-strlcpy-src.c create mode 100644 lib/test_fortify/write_overflow-strlcpy.c create mode 100644 lib/test_fortify/write_overflow-strncpy-src.c create mode 100644 lib/test_fortify/write_overflow-strncpy.c create mode 100644 lib/test_fortify/write_overflow-strscpy.c create mode 100644 scripts/test_fortify.sh (limited to 'scripts') diff --git a/MAINTAINERS b/MAINTAINERS index ca6d6fde85cf..6f4b97dff7ad 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -7323,6 +7323,15 @@ L: netdev@vger.kernel.org S: Maintained F: drivers/net/ethernet/nvidia/* +FORTIFY_SOURCE +M: Kees Cook +L: linux-hardening@vger.kernel.org +S: Supported +F: include/linux/fortify-string.h +F: lib/test_fortify/* +F: scripts/test_fortify.sh +K: \b__NO_FORTIFY\b + FPGA DFL DRIVERS M: Wu Hao R: Tom Rix diff --git a/lib/.gitignore b/lib/.gitignore index 5e7fa54c4536..e5e217b8307b 100644 --- a/lib/.gitignore +++ b/lib/.gitignore @@ -4,3 +4,5 @@ /gen_crc32table /gen_crc64table /oid_registry_data.c +/test_fortify.log +/test_fortify/*.log diff --git a/lib/Makefile b/lib/Makefile index 5efd1b435a37..bd17c2bf43e1 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -360,3 +360,36 @@ obj-$(CONFIG_CMDLINE_KUNIT_TEST) += cmdline_kunit.o obj-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o + +# FORTIFY_SOURCE compile-time behavior tests +TEST_FORTIFY_SRCS = $(wildcard $(srctree)/$(src)/test_fortify/*-*.c) +TEST_FORTIFY_LOGS = $(patsubst $(srctree)/$(src)/%.c, %.log, $(TEST_FORTIFY_SRCS)) +TEST_FORTIFY_LOG = test_fortify.log + +quiet_cmd_test_fortify = TEST $@ + cmd_test_fortify = $(CONFIG_SHELL) $(srctree)/scripts/test_fortify.sh \ + $< $@ "$(NM)" $(CC) $(c_flags) \ + $(call cc-disable-warning,fortify-source) + +targets += $(TEST_FORTIFY_LOGS) +clean-files += $(TEST_FORTIFY_LOGS) +clean-files += $(addsuffix .o, $(TEST_FORTIFY_LOGS)) +$(obj)/test_fortify/%.log: $(src)/test_fortify/%.c \ + $(src)/test_fortify/test_fortify.h \ + $(srctree)/include/linux/fortify-string.h \ + $(srctree)/scripts/test_fortify.sh \ + FORCE + $(call if_changed,test_fortify) + +quiet_cmd_gen_fortify_log = GEN $@ + cmd_gen_fortify_log = cat /dev/null > $@ || true + +targets += $(TEST_FORTIFY_LOG) +clean-files += $(TEST_FORTIFY_LOG) +$(obj)/$(TEST_FORTIFY_LOG): $(addprefix $(obj)/, $(TEST_FORTIFY_LOGS)) FORCE + $(call if_changed,gen_fortify_log) + +# Fake dependency to trigger the fortify tests. +ifeq ($(CONFIG_FORTIFY_SOURCE),y) +$(obj)/string.o: $(obj)/$(TEST_FORTIFY_LOG) +endif diff --git a/lib/test_fortify/read_overflow-memchr.c b/lib/test_fortify/read_overflow-memchr.c new file mode 100644 index 000000000000..2743084b32af --- /dev/null +++ b/lib/test_fortify/read_overflow-memchr.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memchr(small, 0x7A, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/read_overflow-memchr_inv.c b/lib/test_fortify/read_overflow-memchr_inv.c new file mode 100644 index 000000000000..b26e1f1bc217 --- /dev/null +++ b/lib/test_fortify/read_overflow-memchr_inv.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memchr_inv(small, 0x7A, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/read_overflow-memcmp.c b/lib/test_fortify/read_overflow-memcmp.c new file mode 100644 index 000000000000..d5d301ff64ef --- /dev/null +++ b/lib/test_fortify/read_overflow-memcmp.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memcmp(small, large, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/read_overflow-memscan.c b/lib/test_fortify/read_overflow-memscan.c new file mode 100644 index 000000000000..c1a97f2df0f0 --- /dev/null +++ b/lib/test_fortify/read_overflow-memscan.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memscan(small, 0x7A, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/read_overflow2-memcmp.c b/lib/test_fortify/read_overflow2-memcmp.c new file mode 100644 index 000000000000..c6091e640f76 --- /dev/null +++ b/lib/test_fortify/read_overflow2-memcmp.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memcmp(large, small, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/read_overflow2-memcpy.c b/lib/test_fortify/read_overflow2-memcpy.c new file mode 100644 index 000000000000..07b62e56cf16 --- /dev/null +++ b/lib/test_fortify/read_overflow2-memcpy.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memcpy(large, instance.buf, sizeof(large)) + +#include "test_fortify.h" diff --git a/lib/test_fortify/read_overflow2-memmove.c b/lib/test_fortify/read_overflow2-memmove.c new file mode 100644 index 000000000000..34edfab040a3 --- /dev/null +++ b/lib/test_fortify/read_overflow2-memmove.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memmove(large, instance.buf, sizeof(large)) + +#include "test_fortify.h" diff --git a/lib/test_fortify/test_fortify.h b/lib/test_fortify/test_fortify.h new file mode 100644 index 000000000000..d22664fff197 --- /dev/null +++ b/lib/test_fortify/test_fortify.h @@ -0,0 +1,35 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#include +#include +#include +#include + +void do_fortify_tests(void); + +#define __BUF_SMALL 16 +#define __BUF_LARGE 32 +struct fortify_object { + int a; + char buf[__BUF_SMALL]; + int c; +}; + +#define LITERAL_SMALL "AAAAAAAAAAAAAAA" +#define LITERAL_LARGE "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +const char small_src[__BUF_SMALL] = LITERAL_SMALL; +const char large_src[__BUF_LARGE] = LITERAL_LARGE; + +char small[__BUF_SMALL]; +char large[__BUF_LARGE]; +struct fortify_object instance; +size_t size; + +void do_fortify_tests(void) +{ + /* Normal initializations. */ + memset(&instance, 0x32, sizeof(instance)); + memset(small, 0xA5, sizeof(small)); + memset(large, 0x5A, sizeof(large)); + + TEST; +} diff --git a/lib/test_fortify/write_overflow-memcpy.c b/lib/test_fortify/write_overflow-memcpy.c new file mode 100644 index 000000000000..3b3984e428fb --- /dev/null +++ b/lib/test_fortify/write_overflow-memcpy.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memcpy(instance.buf, large_src, sizeof(large_src)) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-memmove.c b/lib/test_fortify/write_overflow-memmove.c new file mode 100644 index 000000000000..640437c3b3e0 --- /dev/null +++ b/lib/test_fortify/write_overflow-memmove.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memmove(instance.buf, large_src, sizeof(large_src)) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-memset.c b/lib/test_fortify/write_overflow-memset.c new file mode 100644 index 000000000000..36e34908cfb3 --- /dev/null +++ b/lib/test_fortify/write_overflow-memset.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + memset(instance.buf, 0x5A, sizeof(large_src)) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strcpy-lit.c b/lib/test_fortify/write_overflow-strcpy-lit.c new file mode 100644 index 000000000000..51effb3e50f9 --- /dev/null +++ b/lib/test_fortify/write_overflow-strcpy-lit.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strcpy(small, LITERAL_LARGE) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strcpy.c b/lib/test_fortify/write_overflow-strcpy.c new file mode 100644 index 000000000000..84f1c56a64c8 --- /dev/null +++ b/lib/test_fortify/write_overflow-strcpy.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strcpy(small, large_src) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strlcpy-src.c b/lib/test_fortify/write_overflow-strlcpy-src.c new file mode 100644 index 000000000000..91bf83ebd34a --- /dev/null +++ b/lib/test_fortify/write_overflow-strlcpy-src.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strlcpy(small, large_src, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strlcpy.c b/lib/test_fortify/write_overflow-strlcpy.c new file mode 100644 index 000000000000..1883db7c0cd6 --- /dev/null +++ b/lib/test_fortify/write_overflow-strlcpy.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strlcpy(instance.buf, large_src, sizeof(instance.buf) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strncpy-src.c b/lib/test_fortify/write_overflow-strncpy-src.c new file mode 100644 index 000000000000..8dcfb8c788dd --- /dev/null +++ b/lib/test_fortify/write_overflow-strncpy-src.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strncpy(small, large_src, sizeof(small) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strncpy.c b/lib/test_fortify/write_overflow-strncpy.c new file mode 100644 index 000000000000..b85f079c815d --- /dev/null +++ b/lib/test_fortify/write_overflow-strncpy.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strncpy(instance.buf, large_src, sizeof(instance.buf) + 1) + +#include "test_fortify.h" diff --git a/lib/test_fortify/write_overflow-strscpy.c b/lib/test_fortify/write_overflow-strscpy.c new file mode 100644 index 000000000000..38feddf377dc --- /dev/null +++ b/lib/test_fortify/write_overflow-strscpy.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define TEST \ + strscpy(instance.buf, large_src, sizeof(instance.buf) + 1) + +#include "test_fortify.h" diff --git a/scripts/test_fortify.sh b/scripts/test_fortify.sh new file mode 100644 index 000000000000..a4da365508f0 --- /dev/null +++ b/scripts/test_fortify.sh @@ -0,0 +1,62 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0-only +set -e + +# Argument 1: Source file to build. +IN="$1" +shift +# Extract just the filename for error messages below. +FILE="${IN##*/}" +# Extract the function name for error messages below. +FUNC="${FILE#*-}" +FUNC="${FUNC%%-*}" +FUNC="${FUNC%%.*}" +# Extract the symbol to test for in build/symbol test below. +WANT="__${FILE%%-*}" + +# Argument 2: Where to write the build log. +OUT="$1" +shift +TMP="${OUT}.tmp" + +# Argument 3: Path to "nm" tool. +NM="$1" +shift + +# Remaining arguments are: $(CC) $(c_flags) + +# Clean up temporary file at exit. +__cleanup() { + rm -f "$TMP" +} +trap __cleanup EXIT + +# Function names in warnings are wrapped in backticks under UTF-8 locales. +# Run the commands with LANG=C so that grep output will not change. +export LANG=C + +status= +# Attempt to build a source that is expected to fail with a specific warning. +if "$@" -Werror -c "$IN" -o "$OUT".o 2> "$TMP" ; then + # If the build succeeds, either the test has failed or the + # warning may only happen at link time (Clang). In that case, + # make sure the expected symbol is unresolved in the symbol list. + # If so, FORTIFY is working for this case. + if ! $NM -A "$OUT".o | grep -m1 "\bU ${WANT}$" >>"$TMP" ; then + status="warning: unsafe ${FUNC}() usage lacked '$WANT' symbol in $IN" + fi +else + # If the build failed, check for the warning in the stderr (gcc). + if ! grep -q -m1 "error: call to .\b${WANT}\b." "$TMP" ; then + status="warning: unsafe ${FUNC}() usage lacked '$WANT' warning in $IN" + fi +fi + +if [ -n "$status" ]; then + # Report on failure results, including compilation warnings. + echo "$status" | tee "$OUT" >&2 +else + # Report on good results, and save any compilation output to log. + echo "ok: unsafe ${FUNC}() usage correctly detected with '$WANT' in $IN" >"$OUT" +fi +cat "$TMP" >>"$OUT" -- cgit v1.2.3 From 3080ea5553cc909b000d1f1d964a9041962f2c5b Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 9 Aug 2021 11:21:23 -0700 Subject: stddef: Introduce DECLARE_FLEX_ARRAY() helper There are many places where kernel code wants to have several different typed trailing flexible arrays. This would normally be done with multiple flexible arrays in a union, but since GCC and Clang don't (on the surface) allow this, there have been many open-coded workarounds, usually involving neighboring 0-element arrays at the end of a structure. For example, instead of something like this: struct thing { ... union { struct type1 foo[]; struct type2 bar[]; }; }; code works around the compiler with: struct thing { ... struct type1 foo[0]; struct type2 bar[]; }; Another case is when a flexible array is wanted as the single member within a struct (which itself is usually in a union). For example, this would be worked around as: union many { ... struct { struct type3 baz[0]; }; }; These kinds of work-arounds cause problems with size checks against such zero-element arrays (for example when building with -Warray-bounds and -Wzero-length-bounds, and with the coming FORTIFY_SOURCE improvements), so they must all be converted to "real" flexible arrays, avoiding warnings like this: fs/hpfs/anode.c: In function 'hpfs_add_sector_to_btree': fs/hpfs/anode.c:209:27: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct bplus_internal_node[0]' [-Wzero-length-bounds] 209 | anode->btree.u.internal[0].down = cpu_to_le32(a); | ~~~~~~~~~~~~~~~~~~~~~~~^~~ In file included from fs/hpfs/hpfs_fn.h:26, from fs/hpfs/anode.c:10: fs/hpfs/hpfs.h:412:32: note: while referencing 'internal' 412 | struct bplus_internal_node internal[0]; /* (internal) 2-word entries giving | ^~~~~~~~ drivers/net/can/usb/etas_es58x/es58x_fd.c: In function 'es58x_fd_tx_can_msg': drivers/net/can/usb/etas_es58x/es58x_fd.c:360:35: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds] 360 | tx_can_msg = (typeof(tx_can_msg))&es58x_fd_urb_cmd->raw_msg[msg_len]; | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:22, from drivers/net/can/usb/etas_es58x/es58x_fd.c:17: drivers/net/can/usb/etas_es58x/es58x_fd.h:231:6: note: while referencing 'raw_msg' 231 | u8 raw_msg[0]; | ^~~~~~~ However, it _is_ entirely possible to have one or more flexible arrays in a struct or union: it just has to be in another struct. And since it cannot be alone in a struct, such a struct must have at least 1 other named member -- but that member can be zero sized. Wrap all this nonsense into the new DECLARE_FLEX_ARRAY() in support of having flexible arrays in unions (or alone in a struct). As with struct_group(), since this is needed in UAPI headers as well, implement the core there, with a non-UAPI wrapper. Additionally update kernel-doc to understand its existence. https://github.com/KSPP/linux/issues/137 Cc: Arnd Bergmann Cc: "Gustavo A. R. Silva" Signed-off-by: Kees Cook --- include/linux/stddef.h | 13 +++++++++++++ include/uapi/linux/stddef.h | 16 ++++++++++++++++ scripts/kernel-doc | 2 ++ 3 files changed, 31 insertions(+) (limited to 'scripts') diff --git a/include/linux/stddef.h b/include/linux/stddef.h index 8b103a53b000..ca507bd5f808 100644 --- a/include/linux/stddef.h +++ b/include/linux/stddef.h @@ -84,4 +84,17 @@ enum { #define struct_group_tagged(TAG, NAME, MEMBERS...) \ __struct_group(TAG, NAME, /* no attrs */, MEMBERS) +/** + * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union + * + * @TYPE: The type of each flexible array element + * @NAME: The name of the flexible array member + * + * In order to have a flexible array member in a union or alone in a + * struct, it needs to be wrapped in an anonymous struct with at least 1 + * named member, but that member can be empty. + */ +#define DECLARE_FLEX_ARRAY(TYPE, NAME) \ + __DECLARE_FLEX_ARRAY(TYPE, NAME) + #endif diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h index 610204f7c275..3021ea25a284 100644 --- a/include/uapi/linux/stddef.h +++ b/include/uapi/linux/stddef.h @@ -25,3 +25,19 @@ struct { MEMBERS } ATTRS; \ struct TAG { MEMBERS } ATTRS NAME; \ } + +/** + * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union + * + * @TYPE: The type of each flexible array element + * @NAME: The name of the flexible array member + * + * In order to have a flexible array member in a union or alone in a + * struct, it needs to be wrapped in an anonymous struct with at least 1 + * named member, but that member can be empty. + */ +#define __DECLARE_FLEX_ARRAY(TYPE, NAME) \ + struct { \ + struct { } __empty_ ## NAME; \ + TYPE NAME[]; \ + } diff --git a/scripts/kernel-doc b/scripts/kernel-doc index 38aa799a776c..5d54b57ff90c 100755 --- a/scripts/kernel-doc +++ b/scripts/kernel-doc @@ -1263,6 +1263,8 @@ sub dump_struct($$) { $members =~ s/DECLARE_KFIFO\s*\($args,\s*$args,\s*$args\)/$2 \*$1/gos; # replace DECLARE_KFIFO_PTR $members =~ s/DECLARE_KFIFO_PTR\s*\($args,\s*$args\)/$2 \*$1/gos; + # replace DECLARE_FLEX_ARRAY + $members =~ s/(?:__)?DECLARE_FLEX_ARRAY\s*\($args,\s*$args\)/$1 $2\[\]/gos; my $declaration = $members; # Split nested struct/union elements as newer ones -- cgit v1.2.3