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Date: Sat, 21 Oct 2017 15:43:03 +0200
From: Nicolas Belouin <nicolas@...ouin.fr>
To: David Howells <dhowells@...hat.com>, "Theodore Ts'o" <tytso@....edu>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Alexander Viro <viro@...iv.linux.org.uk>,
Serge Hallyn <serge@...lyn.com>, Paul Moore <paul@...l-moore.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Eric Paris <eparis@...isplace.org>,
James Morris <james.l.morris@...cle.com>, linux-cachefs@...hat.com,
linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-security-module@...r.kernel.org,
selinux@...ho.nsa.gov, linux-api@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Cc: Nicolas Belouin <nicolas@...ouin.fr>
Subject: [RFC PATCH 2/2] fs: add the possibility to use CAP_SYS_MOUNT to (u)mount a fs
Fulfill the purpose of CAP_SYS_MOUNT by adding it as a sufficient
capability to mount and unmount filesystems.
Signed-off-by: Nicolas Belouin <nicolas@...ouin.fr>
---
fs/cachefiles/daemon.c | 2 +-
fs/ext4/ioctl.c | 2 +-
fs/namespace.c | 3 ++-
fs/super.c | 14 +++++++++-----
4 files changed, 13 insertions(+), 8 deletions(-)
diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 1ee54ffd3a24..fc53bdeacc8a 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -91,7 +91,7 @@ static int cachefiles_daemon_open(struct inode *inode, struct file *file)
_enter("");
/* only the superuser may do this */
- if (!capable(CAP_SYS_ADMIN))
+ if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_MOUNT))
return -EPERM;
/* the cachefiles device may only be open once at a time */
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index afb66d4ab5cf..19d838e558e2 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -458,7 +458,7 @@ static int ext4_shutdown(struct super_block *sb, unsigned long arg)
struct ext4_sb_info *sbi = EXT4_SB(sb);
__u32 flags;
- if (!capable(CAP_SYS_ADMIN))
+ if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_MOUNT))
return -EPERM;
if (get_user(flags, (__u32 __user *)arg))
diff --git a/fs/namespace.c b/fs/namespace.c
index 3b601f115b6c..1eaa6a9f1631 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1661,7 +1661,8 @@ void __detach_mounts(struct dentry *dentry)
*/
static inline bool may_mount(void)
{
- return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
+ return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN) ||
+ ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_MOUNT);
}
static inline bool may_mandlock(void)
diff --git a/fs/super.c b/fs/super.c
index 166c4ee0d0ed..1d84d8b87216 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -474,7 +474,7 @@ struct super_block *sget_userns(struct file_system_type *type,
if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) &&
!(type->fs_flags & FS_USERNS_MOUNT) &&
- !capable(CAP_SYS_ADMIN))
+ !capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_MOUNT))
return ERR_PTR(-EPERM);
retry:
spin_lock(&sb_lock);
@@ -551,7 +551,9 @@ struct super_block *sget(struct file_system_type *type,
user_ns = &init_user_ns;
/* Ensure the requestor has permissions over the target filesystem */
- if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN))
+ if (!(flags & (SB_KERNMOUNT | SB_SUBMOUNT)) &&
+ !ns_capable(user_ns, CAP_SYS_ADMIN) &&
+ !ns_capable(user_ns, CAP_SYS_MOUNT))
return ERR_PTR(-EPERM);
return sget_userns(type, test, set, flags, user_ns, data);
@@ -1020,10 +1022,12 @@ struct dentry *mount_ns(struct file_system_type *fs_type,
{
struct super_block *sb;
- /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
- * over the namespace.
+ /* Don't allow mounting unless the caller has CAP_SYS_ADMIN (deprecated)
+ * or CAP_SYS_MOUNT over the namespace.
*/
- if (!(flags & SB_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
+ if (!(flags & SB_KERNMOUNT) &&
+ !ns_capable(user_ns, CAP_SYS_ADMIN) &&
+ !ns_capable(user_ns, CAP_SYS_MOUNT))
return ERR_PTR(-EPERM);
sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
--
2.14.2
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