[PATCH v2 02/30] fuse: Clear setuid bit even in cache=never path

Vivek Goyal
2019-05-15T19:29:40Z

If fuse daemon is started with cache=never, fuse falls back to direct IO.
In that write path we don't call file_remove_privs() and that means setuid
bit is not cleared if unpriviliged user writes to a file with setuid bit set.

pjdfstest chmod test 12.t tests this and fails.

Fix this by calling fuse_remove_privs() even for direct I/O path.

I tested this as follows.

- Run fuse example pasthrough fs.

$ passthrough_ll /mnt/pasthrough-mnt -o default_permissions,allow_other,cache=never
$ mkdir /mnt/pasthrough-mnt/testdir
$ cd /mnt/pasthrough-mnt/testdir
$ prove -rv pjdfstests/tests/chmod/12.t

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
fs/fuse/file.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 06096b60f1df..5baf07fd2876 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1456,14 +1456,18 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
/* Don't allow parallel writes to the same file */
inode_lock(inode);
res = generic_write_checks(iocb, from);
- if (res > 0) {
- if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
- res = fuse_direct_IO(iocb, from);
- } else {
- res = fuse_direct_io(&io, from, &iocb->ki_pos,
- FUSE_DIO_WRITE);
- }
+ if (res <= 0)
+ goto out;
+
+ res = file_remove_privs(iocb->ki_filp);
+ if (res)
+ goto out;
+ if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
+ res = fuse_direct_IO(iocb, from);
+ } else {
+ res = fuse_direct_io(&io, from, &iocb->ki_pos, FUSE_DIO_WRITE);
}
+out:
fuse_invalidate_attr(inode);
if (res > 0)
fuse_write_update_size(inode, iocb->ki_pos);
--
2.20.1