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Subject[PATCH -V6 11/26] vfs: Add permission flags for setting file attributes
Date
From: Andreas Gruenbacher <agruen@kernel.org>

Some permission models can allow processes to take ownership of a file,
change the file permissions, and set the file timestamps. Introduce new
permission mask flags and check for those permissions in
inode_change_ok().

Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/attr.c | 70 +++++++++++++++++++++++++++++++++++++++++++--------
fs/namei.c | 2 +-
include/linux/fs.h | 4 +++
3 files changed, 64 insertions(+), 12 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index f15e9e3..00578b9 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -14,6 +14,55 @@
#include <linux/fcntl.h>
#include <linux/security.h>

+static int richacl_change_ok(struct inode *inode, int mask)
+{
+ if (!IS_RICHACL(inode))
+ return -EPERM;
+
+ if (inode->i_op->permission)
+ return inode->i_op->permission(inode, mask);
+
+ return check_acl(inode, mask);
+}
+
+static bool inode_uid_change_ok(struct inode *inode, uid_t ia_uid)
+{
+ if (current_fsuid() == inode->i_uid && ia_uid == inode->i_uid)
+ return true;
+ if (current_fsuid() == ia_uid &&
+ richacl_change_ok(inode, MAY_TAKE_OWNERSHIP) == 0)
+ return true;
+ if (capable(CAP_CHOWN))
+ return true;
+ return false;
+}
+
+static bool inode_gid_change_ok(struct inode *inode, gid_t ia_gid)
+{
+ int in_group = in_group_p(ia_gid);
+ if (current_fsuid() == inode->i_uid &&
+ (in_group || ia_gid == inode->i_gid))
+ return true;
+ if (in_group && richacl_change_ok(inode, MAY_TAKE_OWNERSHIP) == 0)
+ return true;
+ if (capable(CAP_CHOWN))
+ return true;
+ return false;
+}
+
+static bool inode_owner_permitted_or_capable(struct inode *inode, int mask)
+{
+ struct user_namespace *ns = inode_userns(inode);
+
+ if (current_user_ns() == ns && current_fsuid() == inode->i_uid)
+ return true;
+ if (richacl_change_ok(inode, mask) == 0)
+ return true;
+ if (ns_capable(ns, CAP_FOWNER))
+ return true;
+ return false;
+}
+
/**
* inode_change_ok - check if attribute changes to an inode are allowed
* @inode: inode to check
@@ -45,21 +94,20 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
return 0;

/* Make sure a caller can chown. */
- if ((ia_valid & ATTR_UID) &&
- (current_fsuid() != inode->i_uid ||
- attr->ia_uid != inode->i_uid) && !capable(CAP_CHOWN))
- return -EPERM;
+ if (ia_valid & ATTR_UID) {
+ if (!inode_uid_change_ok(inode, attr->ia_uid))
+ return -EPERM;
+ }

/* Make sure caller can chgrp. */
- if ((ia_valid & ATTR_GID) &&
- (current_fsuid() != inode->i_uid ||
- (!in_group_p(attr->ia_gid) && attr->ia_gid != inode->i_gid)) &&
- !capable(CAP_CHOWN))
- return -EPERM;
+ if (ia_valid & ATTR_GID) {
+ if (!inode_gid_change_ok(inode, attr->ia_gid))
+ return -EPERM;
+ }

/* Make sure a caller can chmod. */
if (ia_valid & ATTR_MODE) {
- if (!inode_owner_or_capable(inode))
+ if (!inode_owner_permitted_or_capable(inode, MAY_CHMOD))
return -EPERM;
/* Also check the setgid bit! */
if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
@@ -69,7 +117,7 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)

/* Check for setting the inode time. */
if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
- if (!inode_owner_or_capable(inode))
+ if (!inode_owner_permitted_or_capable(inode, MAY_SET_TIMES))
return -EPERM;
}

diff --git a/fs/namei.c b/fs/namei.c
index eacb530..a4d61d1 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -174,7 +174,7 @@ void putname(const char *name)
EXPORT_SYMBOL(putname);
#endif

-static int check_acl(struct inode *inode, int mask)
+int check_acl(struct inode *inode, int mask)
{
#ifdef CONFIG_FS_POSIX_ACL
struct posix_acl *acl;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8afb054..8d5d6e4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -71,6 +71,9 @@ struct inodes_stat_t {
#define MAY_CREATE_DIR 0x00000200
#define MAY_DELETE_CHILD 0x00000400
#define MAY_DELETE_SELF 0x00000800
+#define MAY_TAKE_OWNERSHIP 0x00001000
+#define MAY_CHMOD 0x00002000
+#define MAY_SET_TIMES 0x00004000

/*
* flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond
@@ -2234,6 +2237,7 @@ extern sector_t bmap(struct inode *, sector_t);
extern int notify_change(struct dentry *, struct iattr *);
extern int inode_permission(struct inode *, int);
extern int generic_permission(struct inode *, int);
+extern int check_acl(struct inode *, int);

static inline bool execute_ok(struct inode *inode)
{
--
1.7.4.1


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