diff mbox

[2/2] fs: allow to use dirfd as root for openat and other *at syscalls

Message ID 1466194848-13824-3-git-send-email-avagin@openvz.org
State New, archived
Headers show

Commit Message

Andrey Vagin June 17, 2016, 8:20 p.m. UTC
The problem is that a pathname can contain absolute symlinks and now
they are resolved relative to the current root.

If you want to open a file in another mount namespaces and you have
a file descriptor to its root directory, you probably want that the
pathname is resolved in the target mount namespace and in this case you
can use a new flag O_ATROOT or AT_FDROOT.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
 fs/exec.c                        |  4 +++-
 fs/namei.c                       | 10 ++++++----
 fs/open.c                        |  6 +++++-
 fs/stat.c                        |  4 +++-
 fs/utimes.c                      |  4 +++-
 include/uapi/asm-generic/fcntl.h |  3 +++
 include/uapi/linux/fcntl.h       |  1 +
 7 files changed, 24 insertions(+), 8 deletions(-)
diff mbox

Patch

diff --git a/fs/exec.c b/fs/exec.c
index 887c1c9..473b709 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -775,12 +775,14 @@  static struct file *do_open_execat(int fd, struct filename *name, int flags)
 		.lookup_flags = LOOKUP_FOLLOW,
 	};
 
-	if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+	if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH | AT_FDROOT)) != 0)
 		return ERR_PTR(-EINVAL);
 	if (flags & AT_SYMLINK_NOFOLLOW)
 		open_exec_flags.lookup_flags &= ~LOOKUP_FOLLOW;
 	if (flags & AT_EMPTY_PATH)
 		open_exec_flags.lookup_flags |= LOOKUP_EMPTY;
+	if (flags & AT_FDROOT)
+		open_exec_flags.lookup_flags |= LOOKUP_DFD_ROOT;
 
 	file = do_filp_open(fd, name, &open_exec_flags);
 	if (IS_ERR(file))
diff --git a/fs/namei.c b/fs/namei.c
index 5f08b69..696c9ae 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3577,7 +3577,7 @@  static struct dentry *filename_create(int dfd, struct filename *name,
 	 * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
 	 * other flags passed in are ignored!
 	 */
-	lookup_flags &= LOOKUP_REVAL;
+	lookup_flags &= LOOKUP_REVAL | LOOKUP_DFD_ROOT;
 
 	name = filename_parentat(dfd, name, lookup_flags, path, &last, &type);
 	if (IS_ERR(name))
@@ -4050,7 +4050,7 @@  slashes:
 
 SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
 {
-	if ((flag & ~AT_REMOVEDIR) != 0)
+	if ((flag & ~(AT_REMOVEDIR | AT_FDROOT)) != 0)
 		return -EINVAL;
 
 	if (flag & AT_REMOVEDIR)
@@ -4212,7 +4212,7 @@  SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 	int how = 0;
 	int error;
 
-	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
+	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_FDROOT)) != 0)
 		return -EINVAL;
 	/*
 	 * To use null names we require CAP_DAC_READ_SEARCH
@@ -4227,13 +4227,15 @@  SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 
 	if (flags & AT_SYMLINK_FOLLOW)
 		how |= LOOKUP_FOLLOW;
+	if (flags & AT_FDROOT)
+		how |= LOOKUP_DFD_ROOT;
 retry:
 	error = user_path_at(olddfd, oldname, how, &old_path);
 	if (error)
 		return error;
 
 	new_dentry = user_path_create(newdfd, newname, &new_path,
-					(how & LOOKUP_REVAL));
+				(how & (LOOKUP_REVAL | LOOKUP_DFD_ROOT)));
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
 		goto out;
diff --git a/fs/open.c b/fs/open.c
index 93ae3cd..e0bc8d0 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -613,12 +613,14 @@  SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
 	int error = -EINVAL;
 	int lookup_flags;
 
-	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH | AT_FDROOT)) != 0)
 		goto out;
 
 	lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
 	if (flag & AT_EMPTY_PATH)
 		lookup_flags |= LOOKUP_EMPTY;
+	if (flag & AT_FDROOT)
+		lookup_flags |= LOOKUP_DFD_ROOT;
 retry:
 	error = user_path_at(dfd, filename, lookup_flags, &path);
 	if (error)
@@ -941,6 +943,8 @@  static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
 		lookup_flags |= LOOKUP_DIRECTORY;
 	if (!(flags & O_NOFOLLOW))
 		lookup_flags |= LOOKUP_FOLLOW;
+	if (flags & O_ATROOT)
+		lookup_flags |= LOOKUP_DFD_ROOT;
 	op->lookup_flags = lookup_flags;
 	return 0;
 }
diff --git a/fs/stat.c b/fs/stat.c
index bc045c7..d71e7f2 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -95,13 +95,15 @@  int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
 	unsigned int lookup_flags = 0;
 
 	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
-		      AT_EMPTY_PATH)) != 0)
+		      AT_EMPTY_PATH | AT_FDROOT)) != 0)
 		goto out;
 
 	if (!(flag & AT_SYMLINK_NOFOLLOW))
 		lookup_flags |= LOOKUP_FOLLOW;
 	if (flag & AT_EMPTY_PATH)
 		lookup_flags |= LOOKUP_EMPTY;
+	if (flag & AT_FDROOT)
+		lookup_flags |= LOOKUP_DFD_ROOT;
 retry:
 	error = user_path_at(dfd, filename, lookup_flags, &path);
 	if (error)
diff --git a/fs/utimes.c b/fs/utimes.c
index 85c40f4..78a9eb9 100644
--- a/fs/utimes.c
+++ b/fs/utimes.c
@@ -143,7 +143,7 @@  long do_utimes(int dfd, const char __user *filename, struct timespec *times,
 		goto out;
 	}
 
-	if (flags & ~AT_SYMLINK_NOFOLLOW)
+	if (flags & ~(AT_SYMLINK_NOFOLLOW | AT_FDROOT))
 		goto out;
 
 	if (filename == NULL && dfd != AT_FDCWD) {
@@ -165,6 +165,8 @@  long do_utimes(int dfd, const char __user *filename, struct timespec *times,
 
 		if (!(flags & AT_SYMLINK_NOFOLLOW))
 			lookup_flags |= LOOKUP_FOLLOW;
+		if (flags & AT_FDROOT)
+			lookup_flags |= LOOKUP_DFD_ROOT;
 retry:
 		error = user_path_at(dfd, filename, lookup_flags, &path);
 		if (error)
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index e063eff..28ddbe2 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -61,6 +61,9 @@ 
 #ifndef O_CLOEXEC
 #define O_CLOEXEC	02000000	/* set close_on_exec */
 #endif
+#ifndef O_ATROOT
+#define O_ATROOT	04000000	/* dfd is a root */
+#endif
 
 /*
  * Before Linux 2.6.33 only O_DSYNC semantics were implemented, but using
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index beed138..4f3b631 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -62,6 +62,7 @@ 
 #define AT_SYMLINK_FOLLOW	0x400   /* Follow symbolic links.  */
 #define AT_NO_AUTOMOUNT		0x800	/* Suppress terminal automount traversal */
 #define AT_EMPTY_PATH		0x1000	/* Allow empty relative pathname */
+#define AT_FDROOT		0x2000	/* Resolve a path as if dirfd is root */
 
 
 #endif /* _UAPI_LINUX_FCNTL_H */