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authorEric W. Biederman <ebiederm@xmission.com>2016-06-15 06:59:49 -0500
committerEric W. Biederman <ebiederm@xmission.com>2016-06-23 15:41:57 -0500
commita1935c1738af53249a02290ff7c10e8a6e650a16 (patch)
tree1906ee4f4cacd1d769b947e3d81460404ecceffd /fs/namespace.c
parenta2982cc922c3068783eb9a1f77a5626a1ec36a1f (diff)
downloadlwn-a1935c1738af53249a02290ff7c10e8a6e650a16.tar.gz
lwn-a1935c1738af53249a02290ff7c10e8a6e650a16.zip
mnt: Simplify mount_too_revealing
Verify all filesystems that we check in mount_too_revealing set SB_I_NOEXEC and SB_I_NODEV in sb->s_iflags. That is true for today and it should remain true in the future. Remove the now unnecessary checks from mnt_already_visibile that ensure MNT_LOCK_NOSUID, MNT_LOCK_NOEXEC, and MNT_LOCK_NODEV are preserved. Making the code shorter and easier to read. Relying on SB_I_NOEXEC and SB_I_NODEV instead of the user visible MNT_NOSUID, MNT_NOEXEC, and MNT_NODEV ensures the many current systems where proc and sysfs are mounted with "nosuid, nodev, noexec" and several slightly buggy container applications don't bother to set those flags continue to work. Acked-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c25
1 files changed, 8 insertions, 17 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 2e13f6cfe5df..b1da7f8182c4 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3232,12 +3232,8 @@ static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
continue;
- /* Read the mount flags and filter out flags that
- * may safely be ignored.
- */
+ /* A local view of the mount flags */
mnt_flags = mnt->mnt.mnt_flags;
- if (mnt->mnt.mnt_sb->s_iflags & SB_I_NOEXEC)
- mnt_flags &= ~(MNT_LOCK_NOSUID | MNT_LOCK_NOEXEC);
/* Don't miss readonly hidden in the superblock flags */
if (mnt->mnt.mnt_sb->s_flags & MS_RDONLY)
@@ -3249,15 +3245,6 @@ static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
if ((mnt_flags & MNT_LOCK_READONLY) &&
!(new_flags & MNT_READONLY))
continue;
- if ((mnt_flags & MNT_LOCK_NODEV) &&
- !(new_flags & MNT_NODEV))
- continue;
- if ((mnt_flags & MNT_LOCK_NOSUID) &&
- !(new_flags & MNT_NOSUID))
- continue;
- if ((mnt_flags & MNT_LOCK_NOEXEC) &&
- !(new_flags & MNT_NOEXEC))
- continue;
if ((mnt_flags & MNT_LOCK_ATIME) &&
((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
continue;
@@ -3277,9 +3264,6 @@ static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
}
/* Preserve the locked attributes */
*new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
- MNT_LOCK_NODEV | \
- MNT_LOCK_NOSUID | \
- MNT_LOCK_NOEXEC | \
MNT_LOCK_ATIME);
visible = true;
goto found;
@@ -3292,6 +3276,7 @@ found:
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
{
+ const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
unsigned long s_iflags;
@@ -3303,6 +3288,12 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
if (!(s_iflags & SB_I_USERNS_VISIBLE))
return false;
+ if ((s_iflags & required_iflags) != required_iflags) {
+ WARN_ONCE(1, "Expected s_iflags to contain 0x%lx\n",
+ required_iflags);
+ return true;
+ }
+
return !mnt_already_visible(ns, mnt, new_mnt_flags);
}