Commit fea6d2a6 authored Feb 13, 2017 by Vivek Goyal Committed by Eric W. Biederman Feb 14, 2017

vfs: Use upper filesystem inode in bprm_fill_uid()



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@redhat.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

parent d6cffbbe

fs/exec.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1475,7 +1475,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
		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;

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