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Date: Sat, 27 Nov 2010 20:45:10 +1100
From: Nick Piggin <npiggin@...nel.dk>
To: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 40/46] fs: provide rcu-walk aware permission i_ops
Signed-off-by: Nick Piggin <npiggin@...nel.dk>
---
fs/namei.c | 131 ++++++++++++++++++++++++++++++++++++++++------------
include/linux/fs.h | 6 ++
2 files changed, 107 insertions(+), 30 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index d8f7ece..7fa6119 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -169,8 +169,36 @@ EXPORT_SYMBOL(putname);
/*
* This does basic POSIX ACL permission checking
*/
-static inline int __acl_permission_check(struct inode *inode, int mask,
- int (*check_acl)(struct inode *inode, int mask), int rcu)
+static int acl_permission_check_rcu(struct inode *inode, int mask, unsigned int flags,
+ int (*check_acl_rcu)(struct inode *inode, int mask, unsigned int flags))
+{
+ umode_t mode = inode->i_mode;
+
+ mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
+
+ if (current_fsuid() == inode->i_uid)
+ mode >>= 6;
+ else {
+ if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl_rcu) {
+ int error = check_acl_rcu(inode, mask, flags);
+ if (error != -EAGAIN)
+ return error;
+ }
+
+ if (in_group_p(inode->i_gid))
+ mode >>= 3;
+ }
+
+ /*
+ * If the DACs are ok we don't need any capability check.
+ */
+ if ((mask & ~mode) == 0)
+ return 0;
+ return -EACCES;
+}
+
+static int acl_permission_check(struct inode *inode, int mask, unsigned int flags,
+ int (*check_acl)(struct inode *inode, int mask))
{
umode_t mode = inode->i_mode;
@@ -180,7 +208,7 @@ static inline int __acl_permission_check(struct inode *inode, int mask,
mode >>= 6;
else {
if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {
- if (rcu) {
+ if (flags) {
return -ECHILD;
} else {
int error = check_acl(inode, mask);
@@ -201,10 +229,52 @@ static inline int __acl_permission_check(struct inode *inode, int mask,
return -EACCES;
}
-static inline int acl_permission_check(struct inode *inode, int mask,
- int (*check_acl)(struct inode *inode, int mask))
+/**
+ * generic_permission_rcu - check for access rights on a Posix-like filesystem
+ * @inode: inode to check access rights for
+ * @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
+ * @check_acl_rcu: optional callback to check for Posix ACLs
+ * @flags IPERM_FLAG_ flags.
+ *
+ * Used to check for read/write/execute permissions on a file.
+ * We use "fsuid" for this, letting us set arbitrary permissions
+ * for filesystem access without changing the "normal" uids which
+ * are used for other things.
+ *
+ * generic_permission_rcu must be rcu-walk aware. It should return
+ * -ECHILD in case an rcu-walk request cannot be satisfied (eg.
+ * requires blocking or too much thought!). It would then be called
+ * again in ref-walk mode.
+ */
+int generic_permission_rcu(struct inode *inode, int mask, unsigned int flags,
+ int (*check_acl_rcu)(struct inode *inode, int mask, unsigned int flags))
{
- return __acl_permission_check(inode, mask, check_acl, 0);
+ int ret;
+
+ /*
+ * Do the basic POSIX ACL permission checks.
+ */
+ ret = acl_permission_check_rcu(inode, mask, flags, check_acl_rcu);
+ if (ret != -EACCES)
+ return ret;
+
+ /*
+ * Read/write DACs are always overridable.
+ * Executable DACs are overridable if at least one exec bit is set.
+ */
+ if (!(mask & MAY_EXEC) || execute_ok(inode))
+ if (capable(CAP_DAC_OVERRIDE))
+ return 0;
+
+ /*
+ * Searching includes executable on directories, else just read.
+ */
+ mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
+ if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
+ if (capable(CAP_DAC_READ_SEARCH))
+ return 0;
+
+ return -EACCES;
}
/**
@@ -226,7 +296,7 @@ int generic_permission(struct inode *inode, int mask,
/*
* Do the basic POSIX ACL permission checks.
*/
- ret = acl_permission_check(inode, mask, check_acl);
+ ret = acl_permission_check(inode, mask, 0, check_acl);
if (ret != -EACCES)
return ret;
@@ -282,8 +352,14 @@ int inode_permission(struct inode *inode, int mask)
if (inode->i_op->permission)
retval = inode->i_op->permission(inode, mask);
+ else if (inode->i_op->permission_rcu)
+ retval = inode->i_op->permission_rcu(inode, mask, 0);
+ else if (inode->i_op->check_acl_rcu)
+ retval = generic_permission_rcu(inode, mask, 0,
+ inode->i_op->check_acl_rcu);
else
- retval = generic_permission(inode, mask, inode->i_op->check_acl);
+ retval = generic_permission(inode, mask,
+ inode->i_op->check_acl);
if (retval)
return retval;
@@ -622,22 +698,26 @@ force_reval_path(struct path *path, struct nameidata *nd)
* short-cut DAC fails, then call ->permission() to do more
* complete permission check.
*/
-static inline int __exec_permission(struct inode *inode, int rcu)
+static inline int exec_permission(struct inode *inode, unsigned int flags)
{
int ret;
- if (inode->i_op->permission) {
- if (rcu)
+ if (inode->i_op->permission_rcu) {
+ ret = inode->i_op->permission_rcu(inode, MAY_EXEC, flags);
+ } else if (inode->i_op->permission) {
+ if (flags)
return -ECHILD;
ret = inode->i_op->permission(inode, MAY_EXEC);
- if (!ret)
- goto ok;
- return ret;
+ } else if (inode->i_op->check_acl_rcu) {
+ ret = acl_permission_check_rcu(inode, MAY_EXEC, flags,
+ inode->i_op->check_acl_rcu);
+ } else {
+ ret = acl_permission_check(inode, MAY_EXEC, flags,
+ inode->i_op->check_acl);
}
- ret = __acl_permission_check(inode, MAY_EXEC, inode->i_op->check_acl, rcu);
- if (!ret)
+ if (likely(!ret))
goto ok;
- if (rcu && ret == -ECHILD)
+ if (ret == -ECHILD)
return ret;
if (capable(CAP_DAC_OVERRIDE) || capable(CAP_DAC_READ_SEARCH))
@@ -648,16 +728,6 @@ ok:
return security_inode_permission(inode, MAY_EXEC); /* XXX: ok for RCU? */
}
-static int exec_permission(struct inode *inode)
-{
- return __exec_permission(inode, 0);
-}
-
-static int exec_permission_rcu(struct inode *inode)
-{
- return __exec_permission(inode, 1);
-}
-
static __always_inline void set_root(struct nameidata *nd)
{
if (!nd->root.mnt)
@@ -1126,7 +1196,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
nd->flags |= LOOKUP_CONTINUE;
if (nd->flags & LOOKUP_RCU) {
- err = exec_permission_rcu(nd->inode);
+ err = exec_permission(nd->inode, IPERM_FLAG_RCU);
if (err == -ECHILD) {
if (nameidata_drop_rcu(nd))
return -ECHILD;
@@ -1134,7 +1204,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
}
} else {
exec_again:
- err = exec_permission(nd->inode);
+ err = exec_permission(nd->inode, 0);
}
if (err)
break;
@@ -1567,7 +1637,7 @@ static struct dentry *__lookup_hash(struct qstr *name,
struct dentry *dentry;
int err;
- err = exec_permission(inode);
+ err = exec_permission(inode, 0);
if (err)
return ERR_PTR(err);
@@ -3352,6 +3422,7 @@ EXPORT_SYMBOL(vfs_follow_link);
EXPORT_SYMBOL(vfs_link);
EXPORT_SYMBOL(vfs_mkdir);
EXPORT_SYMBOL(vfs_mknod);
+EXPORT_SYMBOL(generic_permission_rcu);
EXPORT_SYMBOL(generic_permission);
EXPORT_SYMBOL(vfs_readlink);
EXPORT_SYMBOL(vfs_rename);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 07e8a50..490eedd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1549,11 +1549,15 @@ struct file_operations {
int (*setlease)(struct file *, long, struct file_lock **);
};
+#define IPERM_FLAG_RCU 0x0001
+
struct inode_operations {
struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameidata *);
void * (*follow_link) (struct dentry *, struct nameidata *);
int (*permission) (struct inode *, int);
+ int (*permission_rcu) (struct inode *, int, unsigned int);
int (*check_acl)(struct inode *, int);
+ int (*check_acl_rcu)(struct inode *, int, unsigned int);
int (*readlink) (struct dentry *, char __user *,int);
void (*put_link) (struct dentry *, struct nameidata *, void *);
@@ -2164,6 +2168,8 @@ extern sector_t bmap(struct inode *, sector_t);
#endif
extern int notify_change(struct dentry *, struct iattr *);
extern int inode_permission(struct inode *, int);
+extern int generic_permission_rcu(struct inode *, int, unsigned int,
+ int (*check_acl_rcu)(struct inode *, int, unsigned int));
extern int generic_permission(struct inode *, int,
int (*check_acl)(struct inode *, int));
--
1.7.1
--
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