[PATCH v8 09/19] fsnotify: generate pre-content permission event on truncate

Josef Bacik
2024-11-15T15:31:37Z

From: Amir Goldstein <amir73il@gmail.com>

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>
---
fs/open.c | 31 +++++++++++++++++++++----------
include/linux/fsnotify.h | 20 ++++++++++++++++++++
2 files changed, 41 insertions(+), 10 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 1a9483872e1f..d11d373dca80 100644
--- 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 @@ long vfs_truncate(const struct path *path, loff_t length)
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 ce189b4778a5..08893429a818 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -217,6 +217,21 @@ 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)
*/
@@ -255,6 +270,11 @@ 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;
--
2.43.0