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Date: Sun, 30 Jan 2011 00:38:15 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: hch@...radead.org, viro@...iv.linux.org.uk, adilger@....com,
corbet@....net, neilb@...e.de, npiggin@...nel.dk,
hooanon05@...oo.co.jp, bfields@...ldses.org, miklos@...redi.hu
Cc: linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
philippe.deniel@....FR, linux-kernel@...r.kernel.org,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH -V26 12/16] vfs: Add O_PATH open flag
This flag can be used to get a descriptor that is used only
for fetching file attributes. We can get a O_PATH descriptor for even symlink.
A attempt to do any file system operation like read/write/lseek/ioctl will all
fail with EBADF
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
---
fs/fcntl.c | 4 +-
fs/file_table.c | 60 +++++++++++++++++++++++++++++++++++++++++++
fs/namei.c | 38 +++++++++++++++++++++++----
fs/open.c | 16 +++++++++--
include/asm-generic/fcntl.h | 4 +++
include/linux/file.h | 2 +
6 files changed, 113 insertions(+), 11 deletions(-)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index ecc8b39..ba4b564 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -808,14 +808,14 @@ static int __init fcntl_init(void)
* Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
* is defined as O_NONBLOCK on some platforms and not on others.
*/
- BUILD_BUG_ON(18 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
+ BUILD_BUG_ON(19 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
O_RDONLY | O_WRONLY | O_RDWR |
O_CREAT | O_EXCL | O_NOCTTY |
O_TRUNC | O_APPEND | /* O_NONBLOCK | */
__O_SYNC | O_DSYNC | FASYNC |
O_DIRECT | O_LARGEFILE | O_DIRECTORY |
O_NOFOLLOW | O_NOATIME | O_CLOEXEC |
- FMODE_EXEC
+ FMODE_EXEC | O_PATH
));
fasync_cache = kmem_cache_create("fasync_cache",
diff --git a/fs/file_table.c b/fs/file_table.c
index c3e89ad..67b2668 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -284,11 +284,39 @@ struct file *fget(unsigned int fd)
}
rcu_read_unlock();
+ if (file && (file->f_flags & O_PATH)) {
+ /*
+ * O_PATH descriptor need to use
+ * fget_light_lenient() variant
+ */
+ fput(file);
+ file = NULL;
+ }
return file;
}
EXPORT_SYMBOL(fget);
+struct file *fget_lenient(unsigned int fd)
+{
+ struct file *file;
+ struct files_struct *files = current->files;
+
+ rcu_read_lock();
+ file = fcheck_files(files, fd);
+ if (file) {
+ if (!atomic_long_inc_not_zero(&file->f_count)) {
+ /* File object ref couldn't be taken */
+ rcu_read_unlock();
+ return NULL;
+ }
+ }
+ rcu_read_unlock();
+
+ return file;
+}
+EXPORT_SYMBOL(fget_lenient);
+
/*
* Lightweight file lookup - no refcnt increment if fd table isn't shared.
*
@@ -326,6 +354,38 @@ struct file *fget_light(unsigned int fd, int *fput_needed)
rcu_read_unlock();
}
+ if (file && (file->f_flags & O_PATH)) {
+ /*
+ * O_PATH descriptor need to use
+ * fget_light_lenient() variant
+ */
+ if (*fput_needed)
+ fput(file);
+ file = NULL;
+ }
+ return file;
+}
+
+struct file *fget_light_lenient(unsigned int fd, int *fput_needed)
+{
+ struct file *file;
+ struct files_struct *files = current->files;
+
+ *fput_needed = 0;
+ if (atomic_read(&files->count) == 1) {
+ file = fcheck_files(files, fd);
+ } else {
+ rcu_read_lock();
+ file = fcheck_files(files, fd);
+ if (file) {
+ if (atomic_long_inc_not_zero(&file->f_count))
+ *fput_needed = 1;
+ else
+ /* Didn't get the reference, someone's freed */
+ file = NULL;
+ }
+ rcu_read_unlock();
+ }
return file;
}
diff --git a/fs/namei.c b/fs/namei.c
index a8346fa..b9a500c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2115,6 +2115,9 @@ int may_open(struct path *path, int acc_mode, int flag)
if (!inode)
return -ENOENT;
+ if (!(acc_mode & MAY_OPEN))
+ return 0;
+
switch (inode->i_mode & S_IFMT) {
case S_IFLNK:
return -ELOOP;
@@ -2404,8 +2407,10 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
if (!path->dentry->d_inode)
goto exit_dput;
- if (path->dentry->d_inode->i_op->follow_link)
- return NULL;
+ /* We allow open on symlinks with O_PATH flag */
+ if ((open_flag & (O_PATH | O_NOFOLLOW)) != (O_PATH | O_NOFOLLOW))
+ if (path->dentry->d_inode->i_op->follow_link)
+ return NULL;
path_to_nameidata(path, nd);
nd->inode = path->dentry->d_inode;
@@ -2444,6 +2449,14 @@ struct file *do_filp_open(int dfd, const char *pathname,
int flag = open_to_namei_flags(open_flag);
int flags;
+ /*
+ * If we have O_PATH in the open flag. Then we
+ * cannot have anything other than the below set of flags
+ */
+ if ((open_flag & O_PATH) &&
+ (open_flag & ~(O_DIRECTORY|O_NOFOLLOW|O_PATH)))
+ return ERR_PTR(-EINVAL);
+
if (!(open_flag & O_CREAT))
mode = 0;
@@ -2459,7 +2472,7 @@ struct file *do_filp_open(int dfd, const char *pathname,
if (open_flag & __O_SYNC)
open_flag |= O_DSYNC;
- if (!acc_mode)
+ if (!acc_mode && !(open_flag & O_PATH))
acc_mode = MAY_OPEN | ACC_MODE(open_flag);
/* O_TRUNC implies we need access checks for write permissions */
@@ -2499,7 +2512,10 @@ struct file *do_filp_open(int dfd, const char *pathname,
if (unlikely(error))
goto out_filp;
error = -ELOOP;
- if (!(nd.flags & LOOKUP_FOLLOW)) {
+ /*
+ * With allow open on symlinks with O_PATH flag.
+ */
+ if (!(nd.flags & LOOKUP_FOLLOW) && !(open_flag & O_PATH)) {
if (nd.inode->i_op->follow_link)
goto out_path;
}
@@ -2708,10 +2724,19 @@ long do_handle_open(int mountdirfd,
struct file_handle __user *ufh, int open_flag)
{
long retval = 0;
- int fd, acc_mode;
+ int fd, acc_mode = 0;
struct path path;
struct file *filp;
+ /*
+ * If we have O_PATH in the open flag. Then we
+ * cannot have anything other than the below set of flags
+ */
+ if ((open_flag & O_PATH) &&
+ (open_flag & ~(O_DIRECTORY|O_PATH))) {
+ retval = -EINVAL;
+ goto out_err;
+ }
/* can't use O_CREATE with open_by_handle */
if (open_flag & O_CREAT) {
retval = -EINVAL;
@@ -2739,7 +2764,8 @@ long do_handle_open(int mountdirfd,
if (open_flag & __O_SYNC)
open_flag |= O_DSYNC;
- acc_mode = MAY_OPEN | ACC_MODE(open_flag);
+ if (!(open_flag & O_PATH))
+ acc_mode = MAY_OPEN | ACC_MODE(open_flag);
/* O_TRUNC implies we need access checks for write permissions */
if (open_flag & O_TRUNC)
diff --git a/fs/open.c b/fs/open.c
index 1ec2623..7dbde0f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -657,6 +657,9 @@ static inline int __get_file_write_access(struct inode *inode,
return error;
}
+/* empty file_operations to be used for O_PATH descriptor */
+static const struct file_operations o_path_file_operations = {};
+
struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
struct file *f,
int (*open)(struct inode *, struct file *),
@@ -665,8 +668,9 @@ struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
struct inode *inode;
int error;
- f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
- FMODE_PREAD | FMODE_PWRITE;
+ if (!(f->f_flags & O_PATH))
+ f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
+ FMODE_PREAD | FMODE_PWRITE;
inode = dentry->d_inode;
if (f->f_mode & FMODE_WRITE) {
error = __get_file_write_access(inode, mnt);
@@ -680,8 +684,14 @@ struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
f->f_path.dentry = dentry;
f->f_path.mnt = mnt;
f->f_pos = 0;
- f->f_op = fops_get(inode->i_fop);
file_sb_list_add(f, inode->i_sb);
+ /* For O_PATH open we just return without opening the file */
+ if (f->f_flags & O_PATH) {
+ f->f_op = &o_path_file_operations;
+ return f;
+ }
+ f->f_op = fops_get(inode->i_fop);
+
error = security_dentry_open(f, cred);
if (error)
diff --git a/include/asm-generic/fcntl.h b/include/asm-generic/fcntl.h
index 0fc16e3..84793c7 100644
--- a/include/asm-generic/fcntl.h
+++ b/include/asm-generic/fcntl.h
@@ -80,6 +80,10 @@
#define O_SYNC (__O_SYNC|O_DSYNC)
#endif
+#ifndef O_PATH
+#define O_PATH 010000000
+#endif
+
#ifndef O_NDELAY
#define O_NDELAY O_NONBLOCK
#endif
diff --git a/include/linux/file.h b/include/linux/file.h
index e85baeb..e21b733 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -29,6 +29,8 @@ static inline void fput_light(struct file *file, int fput_needed)
extern struct file *fget(unsigned int fd);
extern struct file *fget_light(unsigned int fd, int *fput_needed);
+extern struct file *fget_lenient(unsigned int fd);
+extern struct file *fget_light_lenient(unsigned int fd, int *fput_needed);
extern void set_close_on_exec(unsigned int fd, int flag);
extern void put_filp(struct file *);
extern int alloc_fd(unsigned start, unsigned flags);
--
1.7.1
--
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