* Daniel P. Berrangé (berra...@redhat.com) wrote:
> 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]
OK, updated.
Dave
> > + 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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--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
