From: Darrick J. Wong <djwong@xxxxxxxxxx>
Commit 9f69dfc4e275cc didn't quite get the permissions checking correct:
generic/362 - output mismatch (see /var/tmp/fstests/generic/362.out.bad)
--- tests/generic/362.out 2025-04-30 16:20:44.563833050 -0700
+++ /var/tmp/fstests/generic/362.out.bad 2025-06-11 17:04:24.061193618 -0700
@@ -1,2 +1,3 @@
QA output created by 362
+Failed to open/create file: Operation not permitted
Silence is golden
...
(Run 'diff -u /run/fstests/bin/tests/generic/362.out /var/tmp/fstests/generic/362.out.bad' to see the entire diff)
The kernel allows opening a file for append and truncation. What it
doesn't allow is opening an append-only file for truncation. Note that
this causes generic/079 to regress, but the root cause of that problem
is actually that fuse oddly supports FS_IOC_[GS]ETFLAGS but doesn't
actually set the VFS inode flags.
Cc: <linux-ext4@xxxxxxxxxxxxxxx> # v1.47.3
Fixes: 9f69dfc4e275cc ("fuse2fs: implement O_APPEND correctly")
Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
---
misc/fuse2fs.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index cce1c97c81c075..1debbd3355ec8f 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -2639,15 +2639,13 @@ static int __op_open(struct fuse2fs *ff, const char *path,
file->open_flags |= EXT2_FILE_WRITE;
break;
}
- if (fp->flags & O_APPEND) {
- /* the kernel doesn't allow truncation of an append-only file */
- if (fp->flags & O_TRUNC) {
- ret = -EPERM;
- goto out;
- }
+ /*
+ * If the caller wants to truncate the file, we need to ask for full
+ * write access even if the caller claims to be appending.
+ */
+ if ((fp->flags & O_APPEND) && !(fp->flags & O_TRUNC))
check |= A_OK;
- }
detect_linux_executable_open(fp->flags, &check, &file->open_flags);
