From: Amir Goldstein amir73il@gmail.com
commit 9e46b840c7053b5f7a245e98cd239b60d189a96c upstream.
Overlay file f_pos is the master copy that is preserved through copy up and modified on read/write, but only real fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose limitations that are more strict than ->s_maxbytes for specific files, so we use the real file to perform seeks.
We do not call real fs for SEEK_CUR:0 query and for SEEK_SET:0 requests.
Fixes: d1d04ef8572b ("ovl: stack file ops") Reported-by: Eddie Horng eddiehorng.tw@gmail.com Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/overlayfs/file.c | 44 ++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 40 insertions(+), 4 deletions(-)
--- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -146,11 +146,47 @@ static int ovl_release(struct inode *ino
static loff_t ovl_llseek(struct file *file, loff_t offset, int whence) { - struct inode *realinode = ovl_inode_real(file_inode(file)); + struct inode *inode = file_inode(file); + struct fd real; + const struct cred *old_cred; + ssize_t ret;
- return generic_file_llseek_size(file, offset, whence, - realinode->i_sb->s_maxbytes, - i_size_read(realinode)); + /* + * The two special cases below do not need to involve real fs, + * so we can optimizing concurrent callers. + */ + if (offset == 0) { + if (whence == SEEK_CUR) + return file->f_pos; + + if (whence == SEEK_SET) + return vfs_setpos(file, 0, 0); + } + + ret = ovl_real_fdget(file, &real); + if (ret) + return ret; + + /* + * Overlay file f_pos is the master copy that is preserved + * through copy up and modified on read/write, but only real + * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose + * limitations that are more strict than ->s_maxbytes for specific + * files, so we use the real file to perform seeks. + */ + inode_lock(inode); + real.file->f_pos = file->f_pos; + + old_cred = ovl_override_creds(inode->i_sb); + ret = vfs_llseek(real.file, offset, whence); + revert_creds(old_cred); + + file->f_pos = real.file->f_pos; + inode_unlock(inode); + + fdput(real); + + return ret; }
static void ovl_file_accessed(struct file *file)