On Thu, Dec 12, 2019 at 04:37:52PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: Vivek Goyal <vgo...@redhat.com>
>
> We need to create files in the caller's context. Otherwise after
> creating a file, the caller might not be able to do file operations on
> that file.
>
> Changed effective uid/gid to caller's uid/gid, create file and then
> switch back to uid/gid 0.
>
> Use syscall(setresuid, ...) otherwise glibc does some magic to change EUID
> in all threads, which is not what we want.
>
> Signed-off-by: Vivek Goyal <vgo...@redhat.com>
> Signed-off-by: Miklos Szeredi <mszer...@redhat.com>
> ---
> tools/virtiofsd/passthrough_ll.c | 79 ++++++++++++++++++++++++++++++--
> 1 file changed, 74 insertions(+), 5 deletions(-)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 68bacb6fc5..0188cd9ad6 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> +static int lo_change_cred(fuse_req_t req, struct lo_cred *old)
> +{
> + int res;
> +
> + old->euid = geteuid();
> + old->egid = getegid();
> +
> + res = syscall(SYS_setresgid, -1, fuse_req_ctx(req)->gid, -1);
Do we need to be using SYS_setres[u,g]id32 instead...
[quote setresgid(2)]
The original Linux setresuid() and setresgid() system calls
supported only 16-bit user and group IDs. Subsequently,
Linux 2.4 added setresuid32() and setresgid32(), supporting
32-bit IDs. The glibc setresuid() and setresgid() wrapper
functions transparently deal with the variations across ker‐
nel versions.
[/quote]
> + if (res == -1) {
> + return errno;
> + }
> +
> + res = syscall(SYS_setresuid, -1, fuse_req_ctx(req)->uid, -1);
> + if (res == -1) {
> + int errno_save = errno;
> +
> + syscall(SYS_setresgid, -1, old->egid, -1);
> + return errno_save;
> + }
> +
> + return 0;
> +}
> +
> +/* Regain Privileges */
> +static void lo_restore_cred(struct lo_cred *old)
> +{
> + int res;
> +
> + res = syscall(SYS_setresuid, -1, old->euid, -1);
> + if (res == -1) {
> + fuse_log(FUSE_LOG_ERR, "seteuid(%u): %m\n", old->euid);
> + exit(1);
> + }
> +
> + res = syscall(SYS_setresgid, -1, old->egid, -1);
> + if (res == -1) {
> + fuse_log(FUSE_LOG_ERR, "setegid(%u): %m\n", old->egid);
> + exit(1);
> + }
> +}
> +
> static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent,
> const char *name, mode_t mode, dev_t rdev,
> const char *link)
> @@ -391,12 +443,21 @@ static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t
> parent,
> int saverr;
> struct lo_inode *dir = lo_inode(req, parent);
> struct fuse_entry_param e;
> + struct lo_cred old = {};
>
> saverr = ENOMEM;
>
> + saverr = lo_change_cred(req, &old);
> + if (saverr) {
> + goto out;
> + }
> +
> res = mknod_wrapper(dir->fd, name, link, mode, rdev);
>
> saverr = errno;
> +
> + lo_restore_cred(&old);
> +
> if (res == -1) {
> goto out;
> }
> @@ -794,26 +855,34 @@ static void lo_create(fuse_req_t req, fuse_ino_t
> parent, const char *name,
> struct lo_data *lo = lo_data(req);
> struct fuse_entry_param e;
> int err;
> + struct lo_cred old = {};
>
> if (lo_debug(req)) {
> fuse_log(FUSE_LOG_DEBUG, "lo_create(parent=%" PRIu64 ", name=%s)\n",
> parent, name);
> }
>
> + err = lo_change_cred(req, &old);
> + if (err) {
> + goto out;
> + }
> +
> fd = openat(lo_fd(req, parent), name, (fi->flags | O_CREAT) &
> ~O_NOFOLLOW,
> mode);
> - if (fd == -1) {
> - return (void)fuse_reply_err(req, errno);
> - }
> + err = fd == -1 ? errno : 0;
> + lo_restore_cred(&old);
>
> - fi->fh = fd;
> + if (!err) {
> + fi->fh = fd;
> + err = lo_do_lookup(req, parent, name, &e);
> + }
> if (lo->cache == CACHE_NEVER) {
> fi->direct_io = 1;
> } else if (lo->cache == CACHE_ALWAYS) {
> fi->keep_cache = 1;
> }
>
> - err = lo_do_lookup(req, parent, name, &e);
> +out:
> if (err) {
> fuse_reply_err(req, err);
> } else {
> --
> 2.23.0
>
>
Regards,
Daniel
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