Commit 4acf3bc7 authored by Amir Goldstein's avatar Amir Goldstein Committed by Jan Kara
Browse files

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: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Link: https://patch.msgid.link/23af8201db6ac2efdea94f09ab067d81ba5de7a7.1731684329.git.josef@toxicpanda.com
parent 9740d171

fs/open.c

+21 −10
Original line number Diff line number Diff line
@@ -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);
@@ -175,9 +179,16 @@ 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)

	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);

include/linux/fsnotify.h

+20 −0
Original line number Diff line number Diff line
@@ -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;