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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>
This commit is contained in:
Vivek Goyal 2017-02-13 15:45:26 -05:00 committed by Eric W. Biederman
parent d6cffbbe9a
commit fea6d2a610
1 changed files with 1 additions and 1 deletions
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2
fs/exec.c
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@ -1475,7 +1475,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
if (task_no_new_privs(current)) if (task_no_new_privs(current))
return; return;
inode = file_inode(bprm->file); inode = bprm->file->f_path.dentry->d_inode;
mode = READ_ONCE(inode->i_mode); mode = READ_ONCE(inode->i_mode);
if (!(mode & (S_ISUID|S_ISGID))) if (!(mode & (S_ISUID|S_ISGID)))
return; return;