From fea6d2a610c899bb7fd8e95fcbf46900b886e5a3 Mon Sep 17 00:00:00 2001
From: Vivek Goyal <vgoyal@redhat.com>
Date: Mon, 13 Feb 2017 15:45:26 -0500
Subject: [PATCH] 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>
---
fs/exec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/exec.c b/fs/exec.c
index c195ebb8e2aa..698a86094f76 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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;