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9pfs: fix 'Tgetattr' after unlink 

With a valid file ID (FID) of an open file, it should be possible to send
a 'Tgettattr' 9p request and successfully receive a 'Rgetattr' response,
even if the file has been removed in the meantime. Currently this would
fail with ENOENT.

I.e. this fixes the following misbehaviour with a 9p Linux client:

  open("/home/tst/filename", O_RDWR|O_CREAT|O_EXCL, 0600) = 3
  unlink("/home/tst/filename") = 0
  fstat(3, 0x23aa1a8) = -1 ENOENT (No such file or directory)

Expected results:

  open("/home/tst/filename", O_RDWR|O_CREAT|O_EXCL, 0600) = 3
  unlink("/home/tst/filename") = 0
  fstat(3, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0

This is because 9p server is always using a path name based lstat() call
which fails as soon as the file got removed. So to fix this, use fstat()
whenever we have an open file descriptor already.

Fixes: 00ede4c252 ("virtio-9p: getattr server implementation...")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/103
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <4c41ad47f449a5cc8bfa9285743e029080d5f324.1732465720.git.qemu_oss@crudebyte.com>
This commit is contained in:
Christian Schoenebeck 2024-11-24 16:50:03 +01:00
parent 3bc4db4443
commit c81e7219e0
1 changed files with 7 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
hw/9pfs/9p.c
View File

@ -1596,7 +1596,13 @@ static void coroutine_fn v9fs_getattr(void *opaque)
retval = -ENOENT;
goto out_nofid;
}
retval = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
if ((fidp->fid_type == P9_FID_FILE && fidp->fs.fd != -1) ||
(fidp->fid_type == P9_FID_DIR && fidp->fs.dir.stream))
{
retval = v9fs_co_fstat(pdu, fidp, &stbuf);
} else {
retval = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
}
if (retval < 0) {
goto out;
}