Patch changelog: v2: * Add include <linux/types.h> to openat2.h. [Florian Weimer] * Move OPEN_HOW_SIZE_* constants out of UAPI. [Florian Weimer] * Switch from __aligned_u64 to __u64 since it isn't necessary. [David Laight] v1: https://lore.kernel.org/lkml/20191219105533.12508-1-cyphar@cyphar.com/
While openat2(2) is still not yet in Linus's tree, we can take this opportunity to iron out some small warts that weren't noticed earlier:
* A fix was suggested by Florian Weimer, to separate the openat2 definitions so glibc can use the header directly. I've put the maintainership under VFS but let me know if you'd prefer it belong ot the fcntl folks.
* Having heterogenous field sizes in an extensible struct results in "padding hole" problems when adding new fields (in addition the correct error to use for non-zero padding isn't entirely clear ). The simplest solution is to just copy clone(3)'s model -- always use u64s. It will waste a little more space in the struct, but it removes a possible future headache.
Aleksa Sarai (2): openat2: drop open_how->__padding field uapi: split openat2(2) definitions from fcntl.h
MAINTAINERS | 1 + fs/open.c | 2 - include/linux/fcntl.h | 4 ++ include/uapi/linux/fcntl.h | 37 +----------------- include/uapi/linux/openat2.h | 39 +++++++++++++++++++ tools/testing/selftests/openat2/helpers.h | 7 ++-- .../testing/selftests/openat2/openat2_test.c | 24 ++++-------- 7 files changed, 56 insertions(+), 58 deletions(-) create mode 100644 include/uapi/linux/openat2.h
base-commit: 912dfe068c43fa13c587b8d30e73d335c5ba7d44
The purpose of explicit padding was to allow us to use the space in the future (C provides no guarantee about the value of padding bytes and thus userspace could've provided garbage).
However, the downside of explicit padding is that any extension we wish to add should fit the space exactly (otherwise we may end up with a u16 which will never be used). In addition, the correct error to return for non-zero padding is not clear (-EINVAL doesn't imply "you're using an extension field unsupported by this kernel", but -E2BIG seems a bit odd if the structure size isn't different).
The simplest solution is to just match the design of clone3(2) -- use u64s for all fields. The extra few-bytes cost of extra fields is not significant (it's unlikely configuration structs will ever be extremely large) and it allows for more flag space if necessary. There is also no need to align the u64s because we will not permit any padding in the structure.
As openat2(2) is not yet in Linus's tree, we can iron out these minor warts before we commit to this as a stable ABI.
Acked-by: Christian Brauner christian.brauner@ubuntu.com Suggested-by: David Laight david.laight@aculab.com Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- fs/open.c | 2 -- include/uapi/linux/fcntl.h | 17 +++++++------ tools/testing/selftests/openat2/helpers.h | 7 +++--- .../testing/selftests/openat2/openat2_test.c | 24 +++++++------------ 4 files changed, 19 insertions(+), 31 deletions(-)
diff --git a/fs/open.c b/fs/open.c index 50a46501bcc9..8cdb2b675867 100644 --- a/fs/open.c +++ b/fs/open.c @@ -993,8 +993,6 @@ static inline int build_open_flags(const struct open_how *how, return -EINVAL; if (how->resolve & ~VALID_RESOLVE_FLAGS) return -EINVAL; - if (memchr_inv(how->__padding, 0, sizeof(how->__padding))) - return -EINVAL;
/* Deal with the mode. */ if (WILL_CREATE(flags)) { diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index d886bdb585e4..5aaadfd79dd5 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -101,22 +101,21 @@ #define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
/* - * Arguments for how openat2(2) should open the target path. If @resolve is - * zero, then openat2(2) operates very similarly to openat(2). + * Arguments for how openat2(2) should open the target path. If only @flags and + * @mode are non-zero, then openat2(2) operates very similarly to openat(2). * - * However, unlike openat(2), unknown bits in @flags result in -EINVAL rather - * than being silently ignored. @mode must be zero unless one of {O_CREAT, - * O_TMPFILE} are set. + * However, unlike openat(2), unknown or invalid bits in @flags result in + * -EINVAL rather than being silently ignored. @mode must be zero unless one of + * {O_CREAT, O_TMPFILE} are set. * * @flags: O_* flags. * @mode: O_CREAT/O_TMPFILE file mode. * @resolve: RESOLVE_* flags. */ struct open_how { - __aligned_u64 flags; - __u16 mode; - __u16 __padding[3]; /* must be zeroed */ - __aligned_u64 resolve; + __u64 flags; + __u64 mode; + __u64 resolve; };
#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h index 43ca5ceab6e3..a6ea27344db2 100644 --- a/tools/testing/selftests/openat2/helpers.h +++ b/tools/testing/selftests/openat2/helpers.h @@ -36,10 +36,9 @@ * @resolve: RESOLVE_* flags. */ struct open_how { - __aligned_u64 flags; - __u16 mode; - __u16 __padding[3]; /* must be zeroed */ - __aligned_u64 resolve; + __u64 flags; + __u64 mode; + __u64 resolve; };
#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ diff --git a/tools/testing/selftests/openat2/openat2_test.c b/tools/testing/selftests/openat2/openat2_test.c index 0b64fedc008b..b386367c606b 100644 --- a/tools/testing/selftests/openat2/openat2_test.c +++ b/tools/testing/selftests/openat2/openat2_test.c @@ -40,7 +40,7 @@ struct struct_test { int err; };
-#define NUM_OPENAT2_STRUCT_TESTS 10 +#define NUM_OPENAT2_STRUCT_TESTS 7 #define NUM_OPENAT2_STRUCT_VARIATIONS 13
void test_openat2_struct(void) @@ -57,20 +57,6 @@ void test_openat2_struct(void) .arg.inner.flags = O_RDONLY, .size = sizeof(struct open_how_ext) },
- /* Normal struct with broken padding. */ - { .name = "normal struct (non-zero padding[0])", - .arg.inner.flags = O_RDONLY, - .arg.inner.__padding = {0xa0, 0x00, 0x00}, - .size = sizeof(struct open_how_ext), .err = -EINVAL }, - { .name = "normal struct (non-zero padding[1])", - .arg.inner.flags = O_RDONLY, - .arg.inner.__padding = {0x00, 0x1a, 0x00}, - .size = sizeof(struct open_how_ext), .err = -EINVAL }, - { .name = "normal struct (non-zero padding[2])", - .arg.inner.flags = O_RDONLY, - .arg.inner.__padding = {0x00, 0x00, 0xef}, - .size = sizeof(struct open_how_ext), .err = -EINVAL }, - /* TODO: Once expanded, check zero-padding. */
/* Smaller than version-0 struct. */ @@ -169,7 +155,7 @@ struct flag_test { int err; };
-#define NUM_OPENAT2_FLAG_TESTS 21 +#define NUM_OPENAT2_FLAG_TESTS 23
void test_openat2_flags(void) { @@ -214,9 +200,15 @@ void test_openat2_flags(void) { .name = "invalid how.mode and O_CREAT", .how.flags = O_CREAT, .how.mode = 0xFFFF, .err = -EINVAL }, + { .name = "invalid (very large) how.mode and O_CREAT", + .how.flags = O_CREAT, + .how.mode = 0xC000000000000000ULL, .err = -EINVAL }, { .name = "invalid how.mode and O_TMPFILE", .how.flags = O_TMPFILE | O_RDWR, .how.mode = 0x1337, .err = -EINVAL }, + { .name = "invalid (very large) how.mode and O_TMPFILE", + .how.flags = O_TMPFILE | O_RDWR, + .how.mode = 0x0000A00000000000ULL, .err = -EINVAL },
/* ->resolve must only contain RESOLVE_* flags. */ { .name = "invalid how.resolve and O_RDONLY",
Florian mentioned that glibc doesn't use fcntl.h because it has some issues with namespace cleanliness, and that we should have a separate header for openat2(2) if possible. In addition, userspace has no real use for the OPEN_HOW_SIZE_* constants so move them to the in-kernel headers.
Suggested-by: Florian Weimer fweimer@redhat.com Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- MAINTAINERS | 1 + include/linux/fcntl.h | 4 ++++ include/uapi/linux/fcntl.h | 36 +-------------------------------- include/uapi/linux/openat2.h | 39 ++++++++++++++++++++++++++++++++++++ 4 files changed, 45 insertions(+), 35 deletions(-) create mode 100644 include/uapi/linux/openat2.h
diff --git a/MAINTAINERS b/MAINTAINERS index bd5847e802de..737ada377ac3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -6397,6 +6397,7 @@ F: fs/* F: include/linux/fs.h F: include/linux/fs_types.h F: include/uapi/linux/fs.h +F: include/uapi/linux/openat2.h
FINTEK F75375S HARDWARE MONITOR AND FAN CONTROLLER DRIVER M: Riku Voipio riku.voipio@iki.fi diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index f2eb05bd3af3..7bcdcf4f6ab2 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -21,6 +21,10 @@ (RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \ RESOLVE_BENEATH | RESOLVE_IN_ROOT)
+/* List of all open_how "versions". */ +#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ +#define OPEN_HOW_SIZE_LATEST OPEN_HOW_SIZE_VER0 + #ifndef force_o_largefile #define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T)) #endif diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 5aaadfd79dd5..ca88b7bce553 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -3,6 +3,7 @@ #define _UAPI_LINUX_FCNTL_H
#include <asm/fcntl.h> +#include <linux/openat2.h>
#define F_SETLEASE (F_LINUX_SPECIFIC_BASE + 0) #define F_GETLEASE (F_LINUX_SPECIFIC_BASE + 1) @@ -100,39 +101,4 @@
#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
-/* - * Arguments for how openat2(2) should open the target path. If only @flags and - * @mode are non-zero, then openat2(2) operates very similarly to openat(2). - * - * However, unlike openat(2), unknown or invalid bits in @flags result in - * -EINVAL rather than being silently ignored. @mode must be zero unless one of - * {O_CREAT, O_TMPFILE} are set. - * - * @flags: O_* flags. - * @mode: O_CREAT/O_TMPFILE file mode. - * @resolve: RESOLVE_* flags. - */ -struct open_how { - __u64 flags; - __u64 mode; - __u64 resolve; -}; - -#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ -#define OPEN_HOW_SIZE_LATEST OPEN_HOW_SIZE_VER0 - -/* how->resolve flags for openat2(2). */ -#define RESOLVE_NO_XDEV 0x01 /* Block mount-point crossings - (includes bind-mounts). */ -#define RESOLVE_NO_MAGICLINKS 0x02 /* Block traversal through procfs-style - "magic-links". */ -#define RESOLVE_NO_SYMLINKS 0x04 /* Block traversal through all symlinks - (implies OEXT_NO_MAGICLINKS) */ -#define RESOLVE_BENEATH 0x08 /* Block "lexical" trickery like - "..", symlinks, and absolute - paths which escape the dirfd. */ -#define RESOLVE_IN_ROOT 0x10 /* Make all jumps to "/" and ".." - be scoped inside the dirfd - (similar to chroot(2)). */ - #endif /* _UAPI_LINUX_FCNTL_H */ diff --git a/include/uapi/linux/openat2.h b/include/uapi/linux/openat2.h new file mode 100644 index 000000000000..58b1eb711360 --- /dev/null +++ b/include/uapi/linux/openat2.h @@ -0,0 +1,39 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_LINUX_OPENAT2_H +#define _UAPI_LINUX_OPENAT2_H + +#include <linux/types.h> + +/* + * Arguments for how openat2(2) should open the target path. If only @flags and + * @mode are non-zero, then openat2(2) operates very similarly to openat(2). + * + * However, unlike openat(2), unknown or invalid bits in @flags result in + * -EINVAL rather than being silently ignored. @mode must be zero unless one of + * {O_CREAT, O_TMPFILE} are set. + * + * @flags: O_* flags. + * @mode: O_CREAT/O_TMPFILE file mode. + * @resolve: RESOLVE_* flags. + */ +struct open_how { + __u64 flags; + __u64 mode; + __u64 resolve; +}; + +/* how->resolve flags for openat2(2). */ +#define RESOLVE_NO_XDEV 0x01 /* Block mount-point crossings + (includes bind-mounts). */ +#define RESOLVE_NO_MAGICLINKS 0x02 /* Block traversal through procfs-style + "magic-links". */ +#define RESOLVE_NO_SYMLINKS 0x04 /* Block traversal through all symlinks + (implies OEXT_NO_MAGICLINKS) */ +#define RESOLVE_BENEATH 0x08 /* Block "lexical" trickery like + "..", symlinks, and absolute + paths which escape the dirfd. */ +#define RESOLVE_IN_ROOT 0x10 /* Make all jumps to "/" and ".." + be scoped inside the dirfd + (similar to chroot(2)). */ + +#endif /* _UAPI_LINUX_OPENAT2_H */
[Cc Arnd for struct layout sanity checking]
On December 20, 2019 3:03:27 PM GMT+01:00, Aleksa Sarai cyphar@cyphar.com wrote:
The purpose of explicit padding was to allow us to use the space in the future (C provides no guarantee about the value of padding bytes and thus userspace could've provided garbage).
However, the downside of explicit padding is that any extension we wish to add should fit the space exactly (otherwise we may end up with a u16 which will never be used). In addition, the correct error to return for non-zero padding is not clear (-EINVAL doesn't imply "you're using an extension field unsupported by this kernel", but -E2BIG seems a bit odd if the structure size isn't different).
The simplest solution is to just match the design of clone3(2) -- use u64s for all fields. The extra few-bytes cost of extra fields is not significant (it's unlikely configuration structs will ever be extremely large) and it allows for more flag space if necessary. There is also no need to align the u64s because we will not permit any padding in the structure.
As openat2(2) is not yet in Linus's tree, we can iron out these minor warts before we commit to this as a stable ABI.
Acked-by: Christian Brauner christian.brauner@ubuntu.com Suggested-by: David Laight david.laight@aculab.com Signed-off-by: Aleksa Sarai cyphar@cyphar.com
fs/open.c | 2 -- include/uapi/linux/fcntl.h | 17 +++++++------ tools/testing/selftests/openat2/helpers.h | 7 +++--- .../testing/selftests/openat2/openat2_test.c | 24 +++++++------------ 4 files changed, 19 insertions(+), 31 deletions(-)
diff --git a/fs/open.c b/fs/open.c index 50a46501bcc9..8cdb2b675867 100644 --- a/fs/open.c +++ b/fs/open.c @@ -993,8 +993,6 @@ static inline int build_open_flags(const struct open_how *how, return -EINVAL; if (how->resolve & ~VALID_RESOLVE_FLAGS) return -EINVAL;
if (memchr_inv(how->__padding, 0, sizeof(how->__padding)))
return -EINVAL;/* Deal with the mode. */ if (WILL_CREATE(flags)) {
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index d886bdb585e4..5aaadfd79dd5 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -101,22 +101,21 @@ #define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
/*
- Arguments for how openat2(2) should open the target path. If
@resolve is
- zero, then openat2(2) operates very similarly to openat(2).
- Arguments for how openat2(2) should open the target path. If only
@flags and
- @mode are non-zero, then openat2(2) operates very similarly to
openat(2).
- However, unlike openat(2), unknown bits in @flags result in -EINVAL
rather
- than being silently ignored. @mode must be zero unless one of
{O_CREAT,
- O_TMPFILE} are set.
- However, unlike openat(2), unknown or invalid bits in @flags result
in
- -EINVAL rather than being silently ignored. @mode must be zero
unless one of
- {O_CREAT, O_TMPFILE} are set.
- @flags: O_* flags.
- @mode: O_CREAT/O_TMPFILE file mode.
- @resolve: RESOLVE_* flags.
*/ struct open_how {
- __aligned_u64 flags;
- __u16 mode;
- __u16 __padding[3]; /* must be zeroed */
- __aligned_u64 resolve;
- __u64 flags;
- __u64 mode;
- __u64 resolve;
};
#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h index 43ca5ceab6e3..a6ea27344db2 100644 --- a/tools/testing/selftests/openat2/helpers.h +++ b/tools/testing/selftests/openat2/helpers.h @@ -36,10 +36,9 @@
- @resolve: RESOLVE_* flags.
*/ struct open_how {
- __aligned_u64 flags;
- __u16 mode;
- __u16 __padding[3]; /* must be zeroed */
- __aligned_u64 resolve;
- __u64 flags;
- __u64 mode;
- __u64 resolve;
};
#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ diff --git a/tools/testing/selftests/openat2/openat2_test.c b/tools/testing/selftests/openat2/openat2_test.c index 0b64fedc008b..b386367c606b 100644 --- a/tools/testing/selftests/openat2/openat2_test.c +++ b/tools/testing/selftests/openat2/openat2_test.c @@ -40,7 +40,7 @@ struct struct_test { int err; };
-#define NUM_OPENAT2_STRUCT_TESTS 10 +#define NUM_OPENAT2_STRUCT_TESTS 7 #define NUM_OPENAT2_STRUCT_VARIATIONS 13
void test_openat2_struct(void) @@ -57,20 +57,6 @@ void test_openat2_struct(void) .arg.inner.flags = O_RDONLY, .size = sizeof(struct open_how_ext) },
/* Normal struct with broken padding. */{ .name = "normal struct (non-zero padding[0])",.arg.inner.flags = O_RDONLY,.arg.inner.__padding = {0xa0, 0x00, 0x00},.size = sizeof(struct open_how_ext), .err = -EINVAL },{ .name = "normal struct (non-zero padding[1])",.arg.inner.flags = O_RDONLY,.arg.inner.__padding = {0x00, 0x1a, 0x00},.size = sizeof(struct open_how_ext), .err = -EINVAL },{ .name = "normal struct (non-zero padding[2])",.arg.inner.flags = O_RDONLY,.arg.inner.__padding = {0x00, 0x00, 0xef},.size = sizeof(struct open_how_ext), .err = -EINVAL },/* TODO: Once expanded, check zero-padding. */
/* Smaller than version-0 struct. */
@@ -169,7 +155,7 @@ struct flag_test { int err; };
-#define NUM_OPENAT2_FLAG_TESTS 21 +#define NUM_OPENAT2_FLAG_TESTS 23
void test_openat2_flags(void) { @@ -214,9 +200,15 @@ void test_openat2_flags(void) { .name = "invalid how.mode and O_CREAT", .how.flags = O_CREAT, .how.mode = 0xFFFF, .err = -EINVAL },
{ .name = "invalid (very large) how.mode and O_CREAT",.how.flags = O_CREAT,.how.mode = 0xC000000000000000ULL, .err = -EINVAL },{ .name = "invalid how.mode and O_TMPFILE", .how.flags = O_TMPFILE | O_RDWR, .how.mode = 0x1337, .err = -EINVAL },
{ .name = "invalid (very large) how.mode and O_TMPFILE",.how.flags = O_TMPFILE | O_RDWR,.how.mode = 0x0000A00000000000ULL, .err = -EINVAL },/* ->resolve must only contain RESOLVE_* flags. */ { .name = "invalid how.resolve and O_RDONLY",
linux-kselftest-mirror@lists.linaro.org
-
Aleksa Sarai -
Christian Brauner