fsnotify: generate pre-content permission event on truncate

Generate FS_PRE_ACCESS event before truncate, without sb_writers held.

Move the security hooks also before sb_start_write() to conform with
other security hooks (e.g. in write, fallocate).

The event will have a range info of the page surrounding the new size
to provide an opportunity to fill the conetnt at the end of file before
truncating to non-page aligned size.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/23af8201db6ac2efdea94f09ab067d81ba5de7a7.1731684329.git.josef@toxicpanda.com

diff --git a/fs/open.c b/fs/open.c
index 1a9483872e1f9ba9be2a7accc895165a7a354d11..d11d373dca80881c6a9763292cb7f88e7ec6f2d0 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -81,14 +81,18 @@ long vfs_truncate(const struct path *path, loff_t length)
        if (!S_ISREG(inode->i_mode))
                return -EINVAL;
 
-       error = mnt_want_write(path->mnt);
-       if (error)
-               goto out;
-
        idmap = mnt_idmap(path->mnt);
        error = inode_permission(idmap, inode, MAY_WRITE);
        if (error)
-               goto mnt_drop_write_and_out;
+               return error;
+
+       error = fsnotify_truncate_perm(path, length);
+       if (error)
+               return error;
+
+       error = mnt_want_write(path->mnt);
+       if (error)
+               return error;
 
        error = -EPERM;
        if (IS_APPEND(inode))
@@ -114,7 +118,7 @@ put_write_and_out:
        put_write_access(inode);
 mnt_drop_write_and_out:
        mnt_drop_write(path->mnt);
-out:
+
        return error;
 }
 EXPORT_SYMBOL_GPL(vfs_truncate);
@@ -175,11 +179,18 @@ long do_ftruncate(struct file *file, loff_t length, int small)
        /* Check IS_APPEND on real upper inode */
        if (IS_APPEND(file_inode(file)))
                return -EPERM;
-       sb_start_write(inode->i_sb);
+
        error = security_file_truncate(file);
-       if (!error)
-               error = do_truncate(file_mnt_idmap(file), dentry, length,
-                                   ATTR_MTIME | ATTR_CTIME, file);
+       if (error)
+               return error;
+
+       error = fsnotify_truncate_perm(&file->f_path, length);
+       if (error)
+               return error;
+
+       sb_start_write(inode->i_sb);
+       error = do_truncate(file_mnt_idmap(file), dentry, length,
+                           ATTR_MTIME | ATTR_CTIME, file);
        sb_end_write(inode->i_sb);
 
        return error;

diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 87044acf8e791000b0c0a95b4c3147e007d122ed..1a9ef8f6784ddfe61283b6925cfea90f25496561 100644 (file)
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -170,6 +170,21 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
        return fsnotify_path(&file->f_path, FS_ACCESS_PERM);
 }
 
+/*
+ * fsnotify_truncate_perm - permission hook before file truncate
+ */
+static inline int fsnotify_truncate_perm(const struct path *path, loff_t length)
+{
+       struct inode *inode = d_inode(path->dentry);
+
+       if (!(inode->i_sb->s_iflags & SB_I_ALLOW_HSM) ||
+           !fsnotify_sb_has_priority_watchers(inode->i_sb,
+                                              FSNOTIFY_PRIO_PRE_CONTENT))
+               return 0;
+
+       return fsnotify_pre_content(path, &length, 0);
+}
+
 /*
  * fsnotify_file_perm - permission hook before file access (unknown range)
  */
@@ -208,6 +223,11 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
        return 0;
 }
 
+static inline int fsnotify_truncate_perm(const struct path *path, loff_t length)
+{
+       return 0;
+}
+
 static inline int fsnotify_file_perm(struct file *file, int perm_mask)
 {
        return 0;