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Subject[PATCH 09/27] fs: Push mnt_want_write() outside of i_mutex
Date
Currently, mnt_want_write() is sometimes called with i_mutex held and sometimes
without it. This isn't really a problem because mnt_want_write() is a
non-blocking operation (essentially has a trylock semantics) but when the
function starts to handle also frozen filesystems, it will get a full lock
semantics and thus proper lock ordering has to be established. So move
all mnt_want_write() calls outside of i_mutex.

One non-trivial case needing conversion is kern_path_create() /
user_path_create() which didn't include mnt_want_write() but now needs to
because it acquires i_mutex. Because there are virtual file systems which
don't bother with freeze / remount-ro protection we actually provide both
versions of the function - one which calls mnt_want_write() and one which does
not.

CC: ocfs2-devel@oss.oracle.com
CC: Mark Fasheh <mfasheh@suse.com>
CC: Joel Becker <jlbec@evilplan.org>
CC: "David S. Miller" <davem@davemloft.net>
BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Acked-by: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/namei.c | 115 +++++++++++++++++++++++++++--------------------
fs/ocfs2/refcounttree.c | 10 +---
include/linux/namei.h | 2 +
net/unix/af_unix.c | 13 ++----
4 files changed, 74 insertions(+), 66 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 7d69419..6e65207 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2535,7 +2535,9 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
return file;
}

-struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, int is_dir)
+static struct dentry *do_kern_path_create(int dfd, const char *pathname,
+ struct path *path, int is_dir,
+ int freeze_protect)
{
struct dentry *dentry = ERR_PTR(-EEXIST);
struct nameidata nd;
@@ -2553,6 +2555,14 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL;
nd.intent.open.flags = O_EXCL;

+ if (freeze_protect) {
+ error = mnt_want_write(nd.path.mnt);
+ if (error) {
+ dentry = ERR_PTR(error);
+ goto out;
+ }
+ }
+
/*
* Do the final lookup.
*/
@@ -2581,24 +2591,49 @@ eexist:
dentry = ERR_PTR(-EEXIST);
fail:
mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
+ if (freeze_protect)
+ mnt_drop_write(nd.path.mnt);
out:
path_put(&nd.path);
return dentry;
}
+
+struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, int is_dir)
+{
+ return do_kern_path_create(dfd, pathname, path, is_dir, 0);
+}
EXPORT_SYMBOL(kern_path_create);

+struct dentry *kern_path_create_thawed(int dfd, const char *pathname, struct path *path, int is_dir)
+{
+ return do_kern_path_create(dfd, pathname, path, is_dir, 1);
+}
+EXPORT_SYMBOL(kern_path_create_thawed);
+
struct dentry *user_path_create(int dfd, const char __user *pathname, struct path *path, int is_dir)
{
char *tmp = getname(pathname);
struct dentry *res;
if (IS_ERR(tmp))
return ERR_CAST(tmp);
- res = kern_path_create(dfd, tmp, path, is_dir);
+ res = do_kern_path_create(dfd, tmp, path, is_dir, 0);
putname(tmp);
return res;
}
EXPORT_SYMBOL(user_path_create);

+struct dentry *user_path_create_thawed(int dfd, const char __user *pathname, struct path *path, int is_dir)
+{
+ char *tmp = getname(pathname);
+ struct dentry *res;
+ if (IS_ERR(tmp))
+ return ERR_CAST(tmp);
+ res = do_kern_path_create(dfd, tmp, path, is_dir, 1);
+ putname(tmp);
+ return res;
+}
+EXPORT_SYMBOL(user_path_create_thawed);
+
int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
int error = may_create(dir, dentry);
@@ -2653,7 +2688,7 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
if (S_ISDIR(mode))
return -EPERM;

- dentry = user_path_create(dfd, filename, &path, 0);
+ dentry = user_path_create_thawed(dfd, filename, &path, 0);
if (IS_ERR(dentry))
return PTR_ERR(dentry);

@@ -2662,12 +2697,9 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
error = may_mknod(mode);
if (error)
goto out_dput;
- error = mnt_want_write(path.mnt);
- if (error)
- goto out_dput;
error = security_path_mknod(&path, dentry, mode, dev);
if (error)
- goto out_drop_write;
+ goto out_dput;
switch (mode & S_IFMT) {
case 0: case S_IFREG:
error = vfs_create(path.dentry->d_inode,dentry,mode,NULL);
@@ -2680,11 +2712,10 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
break;
}
-out_drop_write:
- mnt_drop_write(path.mnt);
out_dput:
dput(dentry);
mutex_unlock(&path.dentry->d_inode->i_mutex);
+ mnt_drop_write(path.mnt);
path_put(&path);

return error;
@@ -2726,24 +2757,20 @@ SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
struct path path;
int error;

- dentry = user_path_create(dfd, pathname, &path, 1);
+ dentry = user_path_create_thawed(dfd, pathname, &path, 1);
if (IS_ERR(dentry))
return PTR_ERR(dentry);

if (!IS_POSIXACL(path.dentry->d_inode))
mode &= ~current_umask();
- error = mnt_want_write(path.mnt);
- if (error)
- goto out_dput;
error = security_path_mkdir(&path, dentry, mode);
if (error)
- goto out_drop_write;
+ goto out_dput;
error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
-out_drop_write:
- mnt_drop_write(path.mnt);
out_dput:
dput(dentry);
mutex_unlock(&path.dentry->d_inode->i_mutex);
+ mnt_drop_write(path.mnt);
path_put(&path);
return error;
}
@@ -2838,6 +2865,9 @@ static long do_rmdir(int dfd, const char __user *pathname)
}

nd.flags &= ~LOOKUP_PARENT;
+ error = mnt_want_write(nd.path.mnt);
+ if (error)
+ goto exit1;

mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
dentry = lookup_hash(&nd);
@@ -2848,19 +2878,15 @@ static long do_rmdir(int dfd, const char __user *pathname)
error = -ENOENT;
goto exit3;
}
- error = mnt_want_write(nd.path.mnt);
- if (error)
- goto exit3;
error = security_path_rmdir(&nd.path, dentry);
if (error)
- goto exit4;
+ goto exit3;
error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
-exit4:
- mnt_drop_write(nd.path.mnt);
exit3:
dput(dentry);
exit2:
mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
+ mnt_drop_write(nd.path.mnt);
exit1:
path_put(&nd.path);
putname(name);
@@ -2927,6 +2953,9 @@ static long do_unlinkat(int dfd, const char __user *pathname)
goto exit1;

nd.flags &= ~LOOKUP_PARENT;
+ error = mnt_want_write(nd.path.mnt);
+ if (error)
+ goto exit1;

mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
dentry = lookup_hash(&nd);
@@ -2939,21 +2968,17 @@ static long do_unlinkat(int dfd, const char __user *pathname)
if (!inode)
goto slashes;
ihold(inode);
- error = mnt_want_write(nd.path.mnt);
- if (error)
- goto exit2;
error = security_path_unlink(&nd.path, dentry);
if (error)
- goto exit3;
+ goto exit2;
error = vfs_unlink(nd.path.dentry->d_inode, dentry);
-exit3:
- mnt_drop_write(nd.path.mnt);
- exit2:
+exit2:
dput(dentry);
}
mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
if (inode)
iput(inode); /* truncate the inode here */
+ mnt_drop_write(nd.path.mnt);
exit1:
path_put(&nd.path);
putname(name);
@@ -3013,23 +3038,19 @@ SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
if (IS_ERR(from))
return PTR_ERR(from);

- dentry = user_path_create(newdfd, newname, &path, 0);
+ dentry = user_path_create_thawed(newdfd, newname, &path, 0);
error = PTR_ERR(dentry);
if (IS_ERR(dentry))
goto out_putname;

- error = mnt_want_write(path.mnt);
- if (error)
- goto out_dput;
error = security_path_symlink(&path, dentry, from);
if (error)
- goto out_drop_write;
+ goto out_dput;
error = vfs_symlink(path.dentry->d_inode, dentry, from);
-out_drop_write:
- mnt_drop_write(path.mnt);
out_dput:
dput(dentry);
mutex_unlock(&path.dentry->d_inode->i_mutex);
+ mnt_drop_write(path.mnt);
path_put(&path);
out_putname:
putname(from);
@@ -3122,7 +3143,7 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
if (error)
return error;

- new_dentry = user_path_create(newdfd, newname, &new_path, 0);
+ new_dentry = user_path_create_thawed(newdfd, newname, &new_path, 0);
error = PTR_ERR(new_dentry);
if (IS_ERR(new_dentry))
goto out;
@@ -3130,18 +3151,14 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
error = -EXDEV;
if (old_path.mnt != new_path.mnt)
goto out_dput;
- error = mnt_want_write(new_path.mnt);
- if (error)
- goto out_dput;
error = security_path_link(old_path.dentry, &new_path, new_dentry);
if (error)
- goto out_drop_write;
+ goto out_dput;
error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
-out_drop_write:
- mnt_drop_write(new_path.mnt);
out_dput:
dput(new_dentry);
mutex_unlock(&new_path.dentry->d_inode->i_mutex);
+ mnt_drop_write(new_path.mnt);
path_put(&new_path);
out:
path_put(&old_path);
@@ -3338,6 +3355,10 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
if (newnd.last_type != LAST_NORM)
goto exit2;

+ error = mnt_want_write(oldnd.path.mnt);
+ if (error)
+ goto exit2;
+
oldnd.flags &= ~LOOKUP_PARENT;
newnd.flags &= ~LOOKUP_PARENT;
newnd.flags |= LOOKUP_RENAME_TARGET;
@@ -3373,23 +3394,19 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
if (new_dentry == trap)
goto exit5;

- error = mnt_want_write(oldnd.path.mnt);
- if (error)
- goto exit5;
error = security_path_rename(&oldnd.path, old_dentry,
&newnd.path, new_dentry);
if (error)
- goto exit6;
+ goto exit5;
error = vfs_rename(old_dir->d_inode, old_dentry,
new_dir->d_inode, new_dentry);
-exit6:
- mnt_drop_write(oldnd.path.mnt);
exit5:
dput(new_dentry);
exit4:
dput(old_dentry);
exit3:
unlock_rename(new_dir, old_dir);
+ mnt_drop_write(oldnd.path.mnt);
exit2:
path_put(&newnd.path);
putname(to);
diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index 9f32d7c..dd0c588 100644
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -4453,7 +4453,7 @@ int ocfs2_reflink_ioctl(struct inode *inode,
return error;
}

- new_dentry = user_path_create(AT_FDCWD, newname, &new_path, 0);
+ new_dentry = user_path_create_thawed(AT_FDCWD, newname, &new_path, 0);
error = PTR_ERR(new_dentry);
if (IS_ERR(new_dentry)) {
mlog_errno(error);
@@ -4466,19 +4466,13 @@ int ocfs2_reflink_ioctl(struct inode *inode,
goto out_dput;
}

- error = mnt_want_write(new_path.mnt);
- if (error) {
- mlog_errno(error);
- goto out_dput;
- }
-
error = ocfs2_vfs_reflink(old_path.dentry,
new_path.dentry->d_inode,
new_dentry, preserve);
- mnt_drop_write(new_path.mnt);
out_dput:
dput(new_dentry);
mutex_unlock(&new_path.dentry->d_inode->i_mutex);
+ mnt_drop_write(new_path.mnt);
path_put(&new_path);
out:
path_put(&old_path);
diff --git a/include/linux/namei.h b/include/linux/namei.h
index ffc0213..432f6bb 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -77,7 +77,9 @@ extern int user_path_at_empty(int, const char __user *, unsigned, struct path *,
extern int kern_path(const char *, unsigned, struct path *);

extern struct dentry *kern_path_create(int, const char *, struct path *, int);
+extern struct dentry *kern_path_create_thawed(int, const char *, struct path *, int);
extern struct dentry *user_path_create(int, const char __user *, struct path *, int);
+extern struct dentry *user_path_create_thawed(int, const char __user *, struct path *, int);
extern int kern_path_parent(const char *, struct nameidata *);
extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
const char *, unsigned int, struct path *);
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 641f2e4..37e65a2 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -866,7 +866,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
* Get the parent directory, calculate the hash for last
* component.
*/
- dentry = kern_path_create(AT_FDCWD, sun_path, &path, 0);
+ dentry = kern_path_create_thawed(AT_FDCWD, sun_path, &path, 0);
err = PTR_ERR(dentry);
if (IS_ERR(dentry))
goto out_mknod_parent;
@@ -876,19 +876,13 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
*/
mode = S_IFSOCK |
(SOCK_INODE(sock)->i_mode & ~current_umask());
- err = mnt_want_write(path.mnt);
- if (err)
- goto out_mknod_dput;
err = security_path_mknod(&path, dentry, mode, 0);
if (err)
- goto out_mknod_drop_write;
- err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
-out_mknod_drop_write:
- mnt_drop_write(path.mnt);
- if (err)
goto out_mknod_dput;
+ err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
mutex_unlock(&path.dentry->d_inode->i_mutex);
dput(path.dentry);
+ mnt_drop_write(path.mnt);
path.dentry = dentry;

addr->hash = UNIX_HASH_SIZE;
@@ -925,6 +919,7 @@ out:
out_mknod_dput:
dput(dentry);
mutex_unlock(&path.dentry->d_inode->i_mutex);
+ mnt_drop_write(path.mnt);
path_put(&path);
out_mknod_parent:
if (err == -EEXIST)
--
1.7.1


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