PIDFD_THREAD shares O_EXCL. do_dentry_open() clears O_EXCL after pidfs_export_open() validates the flags, so open_by_handle_at() silently turns a thread pidfd into a process pidfd.
Restore PIDFD_THREAD on the opened file, matching pidfs_alloc_file(), and cover the restored flag with F_GETFL. Signed-off-by: Li Chen <[email protected]> --- fs/pidfs.c | 8 +++++++- tools/testing/selftests/pidfd/pidfd_file_handle_test.c | 1 + 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/pidfs.c b/fs/pidfs.c index aaa609ddab044..c20ffd747ff51 100644 --- a/fs/pidfs.c +++ b/fs/pidfs.c @@ -939,12 +939,18 @@ static int pidfs_export_permission(struct handle_to_path_ctx *ctx, static struct file *pidfs_export_open(const struct path *path, unsigned int oflags) { + struct file *file; + /* * Clear O_LARGEFILE as open_by_handle_at() forces it and raise * O_RDWR as pidfds always are. */ oflags &= ~O_LARGEFILE; - return dentry_open(path, oflags | O_RDWR, current_cred()); + file = dentry_open(path, oflags | O_RDWR, current_cred()); + /* do_dentry_open() strips O_EXCL, which encodes PIDFD_THREAD. */ + if (!IS_ERR(file)) + file->f_flags |= oflags & PIDFD_THREAD; + return file; } static const struct export_operations pidfs_export_operations = { diff --git a/tools/testing/selftests/pidfd/pidfd_file_handle_test.c b/tools/testing/selftests/pidfd/pidfd_file_handle_test.c index 68918734dcf32..1e03ae9575fe6 100644 --- a/tools/testing/selftests/pidfd/pidfd_file_handle_test.c +++ b/tools/testing/selftests/pidfd/pidfd_file_handle_test.c @@ -373,6 +373,7 @@ TEST_F(file_handle, open_by_handle_at_valid_flags) O_CLOEXEC | O_EXCL); ASSERT_GE(pidfd, 0); + ASSERT_NE(fcntl(pidfd, F_GETFL) & PIDFD_THREAD, 0); ASSERT_EQ(fstat(pidfd, &st2), 0); ASSERT_TRUE(st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino); -- 2.52.0
