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Subject[GIT PULL] openat2 fixes
Date
Hi Linus,

/* Summary */
- Remove the unused VALID_UPGRADE_FLAGS define we carried from an extension to
openat2() that we haven't merged. Aleksa might be getting back to it at some
point but just not right now.

- openat2() used to accidently ignore unknown flag values in the upper 32 bits.

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() and add a
compile-time check to catch when we add flags in the upper 32 bit range.

/* Testing */
All patches are based on v5.13-rc3 and have been sitting in linux-next. No
build failures or warnings were observed. All old and new tests are passing.

/* Conflicts */
At the time of creating this PR no merge conflicts were reported from
linux-next and no merge conflicts showed up doing a test-merge with current
mainline.

The following changes since commit c4681547bcce777daf576925a966ffa824edd09d:

Linux 5.13-rc3 (2021-05-23 11:42:48 -1000)

are available in the Git repository at:

git@gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux tags/fs.openat2.unknown_flags.v5.14

for you to fetch changes up to 15845cbcd12a571869c6703892427f9e5839d5fb:

test: add openat2() test for invalid upper 32 bit flag value (2021-05-28 17:44:37 +0200)

Please consider pulling these changes from the signed fs.openat2.unknown_flags.v5.14 tag.

Thanks!
Christian

----------------------------------------------------------------
fs.openat2.unknown_flags.v5.14

----------------------------------------------------------------
Christian Brauner (3):
fcntl: remove unused VALID_UPGRADE_FLAGS
open: don't silently ignore unknown O-flags in openat2()
test: add openat2() test for invalid upper 32 bit flag value

fs/open.c | 14 +++++++++++---
include/linux/fcntl.h | 4 ----
tools/testing/selftests/openat2/openat2_test.c | 7 ++++++-
3 files changed, 17 insertions(+), 8 deletions(-)

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