path: root/security/smack
diff options
authorChristian Brauner <>2021-01-21 14:19:29 +0100
committerChristian Brauner <>2021-01-24 14:27:17 +0100
commit71bc356f93a1c589fad13f7487258f89c417976e (patch)
tree23e5c1b45ae1a6f984f6ed5aee36bef049b72345 /security/smack
parentc7c7a1a18af4c3bb7749d33e3df3acdf0a95bbb5 (diff)
commoncap: handle idmapped mounts
When interacting with user namespace and non-user namespace aware filesystem capabilities the vfs will perform various security checks to determine whether or not the filesystem capabilities can be used by the caller, whether they need to be removed and so on. The main infrastructure for this resides in the capability codepaths but they are called through the LSM security infrastructure even though they are not technically an LSM or optional. This extends the existing security hooks security_inode_removexattr(), security_inode_killpriv(), security_inode_getsecurity() to pass down the mount's user namespace and makes them aware of idmapped mounts. In order to actually get filesystem capabilities from disk the capability infrastructure exposes the get_vfs_caps_from_disk() helper. For user namespace aware filesystem capabilities a root uid is stored alongside the capabilities. In order to determine whether the caller can make use of the filesystem capability or whether it needs to be ignored it is translated according to the superblock's user namespace. If it can be translated to uid 0 according to that id mapping the caller can use the filesystem capabilities stored on disk. If we are accessing the inode that holds the filesystem capabilities through an idmapped mount we map the root uid according to the mount's user namespace. Afterwards the checks are identical to non-idmapped mounts: reading filesystem caps from disk enforces that the root uid associated with the filesystem capability must have a mapping in the superblock's user namespace and that the caller is either in the same user namespace or is a descendant of the superblock's user namespace. For filesystems that are mountable inside user namespace the caller can just mount the filesystem and won't usually need to idmap it. If they do want to idmap it they can create an idmapped mount and mark it with a user namespace they created and which is thus a descendant of s_user_ns. For filesystems that are not mountable inside user namespaces the descendant rule is trivially true because the s_user_ns will be the initial user namespace. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: Cc: Christoph Hellwig <> Cc: David Howells <> Cc: Al Viro <> Cc: Reviewed-by: Christoph Hellwig <> Acked-by: James Morris <> Signed-off-by: Christian Brauner <>
Diffstat (limited to 'security/smack')
1 files changed, 8 insertions, 6 deletions
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 746e5743accc..12a45e61c1a5 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1240,7 +1240,8 @@ static int smack_inode_getattr(const struct path *path)
* Returns 0 if access is permitted, an error code otherwise
-static int smack_inode_setxattr(struct dentry *dentry, const char *name,
+static int smack_inode_setxattr(struct user_namespace *mnt_userns,
+ struct dentry *dentry, const char *name,
const void *value, size_t size, int flags)
struct smk_audit_info ad;
@@ -1362,7 +1363,8 @@ static int smack_inode_getxattr(struct dentry *dentry, const char *name)
* Returns 0 if access is permitted, an error code otherwise
-static int smack_inode_removexattr(struct dentry *dentry, const char *name)
+static int smack_inode_removexattr(struct user_namespace *mnt_userns,
+ struct dentry *dentry, const char *name)
struct inode_smack *isp;
struct smk_audit_info ad;
@@ -1377,7 +1379,7 @@ static int smack_inode_removexattr(struct dentry *dentry, const char *name)
if (!smack_privileged(CAP_MAC_ADMIN))
rc = -EPERM;
} else
- rc = cap_inode_removexattr(dentry, name);
+ rc = cap_inode_removexattr(mnt_userns, dentry, name);
if (rc != 0)
return rc;
@@ -1420,9 +1422,9 @@ static int smack_inode_removexattr(struct dentry *dentry, const char *name)
* Returns the size of the attribute or an error code
-static int smack_inode_getsecurity(struct inode *inode,
- const char *name, void **buffer,
- bool alloc)
+static int smack_inode_getsecurity(struct user_namespace *mnt_userns,
+ struct inode *inode, const char *name,
+ void **buffer, bool alloc)
struct socket_smack *ssp;
struct socket *sock;