Vivek Goyal <vgoyal@xxxxxxxxxx> writes: > Right now bprm_fill_uid() uses inode fetched from file_inode(bprm->file). > This in turn returns inode of lower filesystem (in a stacked filesystem > setup). > > I was playing with modified patches of shiftfs posted by james bottomley > and realized that through shiftfs setuid bit does not take effect. And > reason being that we fetch uid/gid from inode of lower fs (and not from > shiftfs inode). And that results in following checks failing. > > /* We ignore suid/sgid if there are no mappings for them in the ns */ > if (!kuid_has_mapping(bprm->cred->user_ns, uid) || > !kgid_has_mapping(bprm->cred->user_ns, gid)) > return; > > uid/gid fetched from lower fs inode might not be mapped inside the user > namespace of container. So we need to look at uid/gid fetched from > upper filesystem (shiftfs in this particular case) and these should be > mapped and setuid bit can take affect. > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> Applied thanks, Eric > --- > fs/exec.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: rhvgoyal-linux/fs/exec.c > =================================================================== > --- rhvgoyal-linux.orig/fs/exec.c 2017-02-13 15:22:57.107114781 -0500 > +++ rhvgoyal-linux/fs/exec.c 2017-02-13 15:24:19.568114781 -0500 > @@ -1479,7 +1479,7 @@ static void bprm_fill_uid(struct linux_b > if (task_no_new_privs(current)) > return; > > - inode = file_inode(bprm->file); > + inode = bprm->file->f_path.dentry->d_inode; > mode = READ_ONCE(inode->i_mode); > if (!(mode & (S_ISUID|S_ISGID))) > return;
