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fsnotify: generate pre-content permission event on truncate

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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
This commit is contained in:
Amir Goldstein 2024-11-15 10:30:22 -05:00 committed by Jan Kara
parent 9740d17162
commit 4acf3bc76e
2 changed files with 41 additions and 10 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

27
fs/open.c
View file

@ -81,14 +81,18 @@ long vfs_truncate(const struct path *path, loff_t length)
if (!S_ISREG(inode->i_mode)) if (!S_ISREG(inode->i_mode))
return -EINVAL; return -EINVAL;
error = mnt_want_write(path->mnt);
if (error)
goto out;
idmap = mnt_idmap(path->mnt); idmap = mnt_idmap(path->mnt);
error = inode_permission(idmap, inode, MAY_WRITE); error = inode_permission(idmap, inode, MAY_WRITE);
if (error) 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; error = -EPERM;
if (IS_APPEND(inode)) if (IS_APPEND(inode))
@ -114,7 +118,7 @@ long vfs_truncate(const struct path *path, loff_t length)
put_write_access(inode); put_write_access(inode);
mnt_drop_write_and_out: mnt_drop_write_and_out:
mnt_drop_write(path->mnt); mnt_drop_write(path->mnt);
out:
return error; return error;
} }
EXPORT_SYMBOL_GPL(vfs_truncate); 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 */ /* Check IS_APPEND on real upper inode */
if (IS_APPEND(file_inode(file))) if (IS_APPEND(file_inode(file)))
return -EPERM; return -EPERM;
sb_start_write(inode->i_sb);
error = security_file_truncate(file); 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, error = do_truncate(file_mnt_idmap(file), dentry, length,
ATTR_MTIME | ATTR_CTIME, file); ATTR_MTIME | ATTR_CTIME, file);
sb_end_write(inode->i_sb); sb_end_write(inode->i_sb);

20
include/linux/fsnotify.h
View file

@ -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); 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) * 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; 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) static inline int fsnotify_file_perm(struct file *file, int perm_mask)
{ {
return 0; return 0;