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umount: Disallow unprivileged mount force 

Forced unmount affects not just the mount namespace but the underlying
superblock as well.  Restrict forced unmount to the global root user
for now.  Otherwise it becomes possible a user in a less privileged
mount namespace to force the shutdown of a superblock of a filesystem
in a more privileged mount namespace, allowing a DOS attack on root.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2014-10-04 14:44:03 -07:00
parent 4a44a19b47
commit b2f5d4dc38
1 changed files with 3 additions and 0 deletions
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3
fs/namespace.c
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@ -1544,6 +1544,9 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
goto dput_and_out;
if (mnt->mnt.mnt_flags & MNT_LOCKED)
goto dput_and_out;
retval = -EPERM;
if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
goto dput_and_out;
retval = do_umount(mnt, flags);
dput_and_out: