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Re: [PATCH v3 06/10] virtiofsd: Let lo_inode_open() return a TempFd
From: |
Vivek Goyal |
Subject: |
Re: [PATCH v3 06/10] virtiofsd: Let lo_inode_open() return a TempFd |
Date: |
Fri, 6 Aug 2021 15:55:01 -0400 |
On Fri, Jul 30, 2021 at 05:01:30PM +0200, Max Reitz wrote:
> Strictly speaking, this is not necessary, because lo_inode_open() will
> always return a new FD owned by the caller, so TempFd.owned will always
> be true.
>
> However, auto-cleanup is nice, and in some cases this plays nicely with
> an lo_inode_fd() call in another conditional branch (see lo_setattr()).
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
> tools/virtiofsd/passthrough_ll.c | 138 +++++++++++++------------------
> 1 file changed, 59 insertions(+), 79 deletions(-)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 9e1bc37af8..292b7f7e27 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -291,10 +291,8 @@ static void temp_fd_clear(TempFd *temp_fd)
> /**
> * Return an owned fd from *temp_fd that will not be closed when
> * *temp_fd goes out of scope.
> - *
> - * (TODO: Remove __attribute__ once this is used.)
> */
> -static __attribute__((unused)) int temp_fd_steal(TempFd *temp_fd)
> +static int temp_fd_steal(TempFd *temp_fd)
> {
> if (temp_fd->owned) {
> temp_fd->owned = false;
> @@ -673,9 +671,12 @@ static int lo_fd(fuse_req_t req, fuse_ino_t ino, TempFd
> *tfd)
> * when a malicious client opens special files such as block device nodes.
> * Symlink inodes are also rejected since symlinks must already have been
> * traversed on the client side.
> + *
> + * The fd is returned in tfd->fd. The return value is 0 on success and
> -errno
> + * otherwise.
> */
> -static int lo_inode_open(struct lo_data *lo, struct lo_inode *inode,
> - int open_flags)
> +static int lo_inode_open(const struct lo_data *lo, const struct lo_inode
> *inode,
> + int open_flags, TempFd *tfd)
> {
> g_autofree char *fd_str = g_strdup_printf("%d", inode->fd);
> int fd;
> @@ -694,7 +695,13 @@ static int lo_inode_open(struct lo_data *lo, struct
> lo_inode *inode,
> if (fd < 0) {
> return -errno;
> }
> - return fd;
> +
> + *tfd = (TempFd) {
> + .fd = fd,
> + .owned = true,
> + };
> +
> + return 0;
> }
>
> static void lo_init(void *userdata, struct fuse_conn_info *conn)
> @@ -852,7 +859,12 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino,
> struct stat *attr,
> return;
> }
>
> - res = lo_inode_fd(inode, &inode_fd);
> + if (!fi && (valid & FUSE_SET_ATTR_SIZE)) {
> + /* We need an O_RDWR FD for ftruncate() */
> + res = lo_inode_open(lo, inode, O_RDWR, &inode_fd);
> + } else {
> + res = lo_inode_fd(inode, &inode_fd);
> + }
A minor nit.
So inode_fd could hold either an O_PATH fd returned by lo_inode_fd()
or a O_RDWR fd returned by lo_inode_open().
Previous code held these fds in two different variables, inode_fd and
truncfd respectively. I kind of found that easier to read because looking
at variable name, I knew whether I am dealing with O_PATH fd or an
O_RDWR fd I just opened.
So a minor nit. We could continue to have two variables, say
inode_fd and trunc_fd. Just that type of trunc_fd will now be TempFd.
Also I liked previous style easier to read where I always got hold
of O_PATH fd first. And later opened a O_RDWR fd if operation
is FUSE_ATTR_SIZE. So "valid & FUSE_SET_ATTR_SIZE" check was not
at two places.
Anyway, this is a minor nit. If you don't like the idea of using
two separate variables to hold O_PATH fd and O_RDWR fd, that's ok.
> if (res < 0) {
> saverr = -res;
> goto out_err;
> @@ -900,18 +912,11 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino,
> struct stat *attr,
> if (fi) {
> truncfd = fd;
> } else {
> - truncfd = lo_inode_open(lo, inode, O_RDWR);
> - if (truncfd < 0) {
> - saverr = -truncfd;
> - goto out_err;
> - }
> + truncfd = inode_fd.fd;
> }
>
> saverr = drop_security_capability(lo, truncfd);
> if (saverr) {
> - if (!fi) {
> - close(truncfd);
> - }
> goto out_err;
> }
>
> @@ -919,9 +924,6 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino,
> struct stat *attr,
> res = drop_effective_cap("FSETID", &cap_fsetid_dropped);
> if (res != 0) {
> saverr = res;
> - if (!fi) {
> - close(truncfd);
> - }
> goto out_err;
> }
> }
> @@ -934,9 +936,6 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino,
> struct stat *attr,
> fuse_log(FUSE_LOG_ERR, "Failed to gain CAP_FSETID\n");
> }
> }
> - if (!fi) {
> - close(truncfd);
> - }
> if (res == -1) {
> goto out_err;
> }
> @@ -1822,11 +1821,12 @@ static struct lo_dirp *lo_dirp(fuse_req_t req, struct
> fuse_file_info *fi)
> static void lo_opendir(fuse_req_t req, fuse_ino_t ino,
> struct fuse_file_info *fi)
> {
> + g_auto(TempFd) inode_fd = TEMP_FD_INIT;
> int error = ENOMEM;
> struct lo_data *lo = lo_data(req);
> struct lo_inode *inode;
> struct lo_dirp *d = NULL;
> - int fd;
> + int res;
> ssize_t fh;
>
> inode = lo_inode(req, ino);
> @@ -1840,13 +1840,13 @@ static void lo_opendir(fuse_req_t req, fuse_ino_t ino,
> goto out_err;
> }
>
> - fd = lo_inode_open(lo, inode, O_RDONLY);
> - if (fd < 0) {
> - error = -fd;
> + res = lo_inode_open(lo, inode, O_RDONLY, &inode_fd);
> + if (res < 0) {
> + error = -res;
> goto out_err;
> }
>
> - d->dp = fdopendir(fd);
> + d->dp = fdopendir(temp_fd_steal(&inode_fd));
So we are using temp_fd_steal(), because if fdopendir() is succesful,
we don't want to close fd instead it will be closed during closedir()
call. inode_fd will be closed once lo_opendir(), so we get fd ownership
which will need to close explicitly, when appropriate.
Who closes the stolen fd returned by temp_fd_steal() if fdopendir() fails?
> if (d->dp == NULL) {
> goto out_errno;
> }
> @@ -1876,8 +1876,6 @@ out_err:
> if (d) {
> if (d->dp) {
> closedir(d->dp);
> - } else if (fd != -1) {
> - close(fd);
> }
> free(d);
> }
> @@ -2077,6 +2075,7 @@ static void update_open_flags(int writeback, int
> allow_direct_io,
> static int lo_do_open(struct lo_data *lo, struct lo_inode *inode,
> int existing_fd, struct fuse_file_info *fi)
> {
> + g_auto(TempFd) inode_fd = TEMP_FD_INIT;
It bothers me that we are using variable inode_fd both to hold O_PATH
fd as well as regular fd. Will be nice if just by looking at variable
name I could figure out which type of fd it is.
Will it make sense to use path_fd, or ipath_fd, or inode_path_fd to
represent where we are using O_PATH fd.
Thanks
Vivek
- Re: [PATCH v3 06/10] virtiofsd: Let lo_inode_open() return a TempFd,
Vivek Goyal <=