From: Darrick J. Wong <djwong@kernel.org>
Date: Thu, 28 Aug 2025 17:30:38 +0000 (-0700)
Subject: libext2fs: don't look for O_EXCL in the F_GETFL output
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4832dc95d2385c4efdec28d4ca95380be8234f49;p=thirdparty%2Fe2fsprogs.git

libext2fs: don't look for O_EXCL in the F_GETFL output

For decades, Linux has never propagated O_EXCL into the user-visible
file flags in do_dentry_open:

	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

Therefore, one cannot use F_GETFL to determine if the file was opened
with O_EXCL.  The unixfd IO manager will have to trust that the caller
opened the file in O_EXCL mode.  Without this patch, the upcoming flock
patch will not work correctly in determining the lock mode to keep other
copies of fuse4fs and/or systemd from touching a fuse4fs mounted
filesystem.

Cc: <linux-ext4@vger.kernel.org> # v1.43.2
Fixes: 4ccf9e4fe165cf ("libext2fs: add unixfd_io_manager")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---

diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index adbdd5f6..723a5c24 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -1090,11 +1090,10 @@ static errcode_t unixfd_open(const char *str_fd, int flags,
 	if (fd_flags == -1)
 		return EBADF;
 
-	flags = 0;
+	/* O_EXCL is cleared by Linux at open and not returned by F_GETFL */
+	flags &= IO_FLAG_EXCLUSIVE;
 	if (fd_flags & O_RDWR)
 		flags |= IO_FLAG_RW;
-	if (fd_flags & O_EXCL)
-		flags |= IO_FLAG_EXCLUSIVE;
 #if defined(O_DIRECT)
 	if (fd_flags & O_DIRECT)
 		flags |= IO_FLAG_DIRECT_IO;