[LTP] [PATCH v2] accept03/tst_fd: Harden parallel runs against shared path races

[Stephen Bertram]

From: Stephen Bertram <sbertram@redhat.com>

Concurrent syscall runs can TBROK in tst_fd when multiple processes
race on fixed fd_file/fd_dir names (unlink ENOENT). Use pid-unique
paths with O_EXCL, distinct names for the file and O_PATH cases.

This covers accept03, epoll_pwait06, ioctl_pidfd01, and splice07,
which call TST_FD_FOREACH without a private tmpdir.

Signed-off-by: Stephen Bertram <sbertram@redhat.com>
---
 lib/tst_fd.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/lib/tst_fd.c b/lib/tst_fd.c
index 6538a098c..5d4430cf8 100644
--- a/lib/tst_fd.c
+++ b/lib/tst_fd.c
@@ -30,29 +30,42 @@ struct tst_fd_desc {
 	const char *desc;
 };
 
+static void fd_path(char *buf, size_t len, const char *prefix)
+{
+	snprintf(buf, len, "%s_%d", prefix, getpid());
+}
+
 static void open_file(struct tst_fd *fd)
 {
-	fd->fd = SAFE_OPEN("fd_file", O_RDWR | O_CREAT, 0666);
-	SAFE_UNLINK("fd_file");
+	char path[64];
+
+	fd_path(path, sizeof(path), "fd_file");
+	fd->fd = SAFE_OPEN(path, O_RDWR | O_CREAT | O_EXCL, 0666);
+	SAFE_UNLINK(path);
 }
 
 static void open_path(struct tst_fd *fd)
 {
+	char path[64];
 	int tfd;
 
-	tfd = SAFE_CREAT("fd_file", 0666);
+	fd_path(path, sizeof(path), "fd_path");
+	tfd = SAFE_OPEN(path, O_RDWR | O_CREAT | O_EXCL, 0666);
 	SAFE_CLOSE(tfd);
 
-	fd->fd = SAFE_OPEN("fd_file", O_PATH);
+	fd->fd = SAFE_OPEN(path, O_PATH);
 
-	SAFE_UNLINK("fd_file");
+	SAFE_UNLINK(path);
 }
 
 static void open_dir(struct tst_fd *fd)
 {
-	SAFE_MKDIR("fd_dir", 0700);
-	fd->fd = SAFE_OPEN("fd_dir", O_DIRECTORY);
-	SAFE_RMDIR("fd_dir");
+	char path[64];
+
+	fd_path(path, sizeof(path), "fd_dir");
+	SAFE_MKDIR(path, 0700);
+	fd->fd = SAFE_OPEN(path, O_DIRECTORY);
+	SAFE_RMDIR(path);
 }
 
 static void open_dev_zero(struct tst_fd *fd)
-- 
2.55.0