From 5c350aa11b441b32baf3bfe4018168cb8d10cef7 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 28 May 2021 11:24:15 +0200 Subject: [PATCH 1/3] fcntl: remove unused VALID_UPGRADE_FLAGS We currently do not maky use of this feature and should we implement something like this in the future it's trivial to add it back. Link: https://lore.kernel.org/r/20210528092417.3942079-2-brauner@kernel.org Cc: Christoph Hellwig Cc: Aleksa Sarai Cc: Al Viro Cc: linux-fsdevel@vger.kernel.org Suggested-by: Richard Guy Briggs Reviewed-by: Richard Guy Briggs Reviewed-by: Christoph Hellwig Signed-off-by: Christian Brauner --- include/linux/fcntl.h | 4 ---- 1 file changed, 4 deletions(-) diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index 766fcd973beb..a332e79b3207 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -12,10 +12,6 @@ FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) -/* List of all valid flags for the how->upgrade_mask argument: */ -#define VALID_UPGRADE_FLAGS \ - (UPGRADE_NOWRITE | UPGRADE_NOREAD) - /* List of all valid flags for the how->resolve argument: */ #define VALID_RESOLVE_FLAGS \ (RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \ From cfe80306a0dd6d363934913e47c3f30d71b721e5 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 28 May 2021 11:24:16 +0200 Subject: [PATCH 2/3] open: don't silently ignore unknown O-flags in openat2() The new openat2() syscall verifies that no unknown O-flag values are set and returns an error to userspace if they are while the older open syscalls like open() and openat() simply ignore unknown flag values: #define O_FLAG_CURRENTLY_INVALID (1 << 31) struct open_how how = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID, .resolve = 0, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how, sizeof(how)); /* succeeds */ fd = openat(-EBADF, "/dev/null", O_RDONLY | O_FLAG_CURRENTLY_INVALID); However, openat2() silently truncates the upper 32 bits meaning: #define O_FLAG_CURRENTLY_INVALID_LOWER32 (1 << 31) #define O_FLAG_CURRENTLY_INVALID_UPPER32 (1 << 40) struct open_how how_lowe32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_LOWER32, }; struct open_how how_upper32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_UPPER32, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how_lower32, sizeof(how_lower32)); /* succeeds */ fd = openat2(-EBADF, "/dev/null", &how_upper32, sizeof(how_upper32)); Fix this by preventing the immediate truncation in build_open_flags(). There's a snafu here though stripping FMODE_* directly from flags would cause the upper 32 bits to be truncated as well due to integer promotion rules since FMODE_* is unsigned int, O_* are signed ints (yuck). In addition, struct open_flags currently defines flags to be 32 bit which is reasonable. If we simply were to bump it to 64 bit we would need to change a lot of code preemptively which doesn't seem worth it. So simply add a compile-time check verifying that all currently known O_* flags are within the 32 bit range and fail to build if they aren't anymore. This change shouldn't regress old open syscalls since they silently truncate any unknown values anyway. It is a tiny semantic change for openat2() but it is very unlikely people pass ing > 32 bit unknown flags and the syscall is relatively new too. Link: https://lore.kernel.org/r/20210528092417.3942079-3-brauner@kernel.org Cc: Christoph Hellwig Cc: Aleksa Sarai Cc: Al Viro Cc: linux-fsdevel@vger.kernel.org Reported-by: Richard Guy Briggs Reviewed-by: Christoph Hellwig Reviewed-by: Aleksa Sarai Reviewed-by: Richard Guy Briggs Signed-off-by: Christian Brauner --- fs/open.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/open.c b/fs/open.c index e53af13b5835..53bc0573c0ec 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1002,12 +1002,20 @@ inline struct open_how build_open_how(int flags, umode_t mode) inline int build_open_flags(const struct open_how *how, struct open_flags *op) { - int flags = how->flags; + u64 flags = how->flags; + u64 strip = FMODE_NONOTIFY | O_CLOEXEC; int lookup_flags = 0; int acc_mode = ACC_MODE(flags); - /* Must never be set by userspace */ - flags &= ~(FMODE_NONOTIFY | O_CLOEXEC); + BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS), + "struct open_flags doesn't yet handle flags > 32 bits"); + + /* + * Strip flags that either shouldn't be set by userspace like + * FMODE_NONOTIFY or that aren't relevant in determining struct + * open_flags like O_CLOEXEC. + */ + flags &= ~strip; /* * Older syscalls implicitly clear all of the invalid flags or argument From 15845cbcd12a571869c6703892427f9e5839d5fb Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 28 May 2021 11:24:17 +0200 Subject: [PATCH 3/3] test: add openat2() test for invalid upper 32 bit flag value Test that openat2() rejects unknown flags in the upper 32 bit range. Link: https://lore.kernel.org/r/20210528092417.3942079-4-brauner@kernel.org Cc: Richard Guy Briggs Cc: Aleksa Sarai Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Richard Guy Briggs Signed-off-by: Christian Brauner --- tools/testing/selftests/openat2/openat2_test.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/openat2/openat2_test.c b/tools/testing/selftests/openat2/openat2_test.c index 381d874cce99..d7ec1e7da0d0 100644 --- a/tools/testing/selftests/openat2/openat2_test.c +++ b/tools/testing/selftests/openat2/openat2_test.c @@ -155,7 +155,7 @@ struct flag_test { int err; }; -#define NUM_OPENAT2_FLAG_TESTS 24 +#define NUM_OPENAT2_FLAG_TESTS 25 void test_openat2_flags(void) { @@ -229,6 +229,11 @@ void test_openat2_flags(void) { .name = "invalid how.resolve and O_PATH", .how.flags = O_PATH, .how.resolve = 0x1337, .err = -EINVAL }, + + /* currently unknown upper 32 bit rejected. */ + { .name = "currently unknown bit (1 << 63)", + .how.flags = O_RDONLY | (1ULL << 63), + .how.resolve = 0, .err = -EINVAL }, }; BUILD_BUG_ON(ARRAY_LEN(tests) != NUM_OPENAT2_FLAG_TESTS);