[PATCH 2/2] fs: allow to use dirfd as root for openat and other *at syscalls
From: Andrey Vagin
Date: Fri Jun 17 2016 - 16:21:05 EST
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@xxxxxxxxxx>
---
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 --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 */
--
2.5.5