Re: [PATCH 5/7] ecryptfs: sanitize struct iattr handling in truncate_upper

On 2026-04-06 00:58:23, Tyler Hicks wrote:
> On 2026-03-31 17:37:26, Christoph Hellwig wrote:
> > Currently the two callers of truncate_upper handle passing information
> > very differently.  ecryptfs_truncate passes a zeroed lower_ia and expects
> > truncate_upper to fill it in from the upper ia created just for that,
> > while ecryptfs_setattr passes a fully initialized lower_ia copied from
> > the upper one.
> > 
> > Switch to only passing a lower ia which must have ia_size set to the
> > expected lower size, which cleans up the logic in truncate_upper and
> > ecryptfs_truncate.
> 
> This one isn't making sense to me. It is shoving the upper inode size
> into the lower_ia->ia_size, which are two different values for encrypted
> files. I find that it makes truncate_upper() more confusing to read.
> 
> I'm wondering if the following function signature would make more sense
> so that we can make better sense of which inode size we're talking about:
> 
>  static int truncate_upper(struct dentry *dentry, size_t upper_size,
> 			   struct iattr *lower_ia)

Err... that was a bad suggestion. upper_size should be a loff_t but, now
that I'm at the end of the patch series review, I see that's essentially
the signature of ecryptfs_truncate() but I'm still not understanding why
we're sticking the upper inode size into the lower_ia.

Tyler

> 
> Tyler
> 
> > 
> > Signed-off-by: Christoph Hellwig <[email protected]>
> > ---
> >  fs/ecryptfs/inode.c | 39 ++++++++++++++++++---------------------
> >  1 file changed, 18 insertions(+), 21 deletions(-)
> > 
> > diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> > index 7a3da72eb3c6..a7dc25fae8ee 100644
> > --- a/fs/ecryptfs/inode.c
> > +++ b/fs/ecryptfs/inode.c
> > @@ -709,7 +709,6 @@ upper_size_to_lower_size(struct ecryptfs_crypt_stat *crypt_stat,
> >  /**
> >   * truncate_upper
> >   * @dentry: The ecryptfs layer dentry
> > - * @ia: Address of the ecryptfs inode's attributes
> >   * @lower_ia: Address of the lower inode's attributes
> >   *
> >   * Function to handle truncations modifying the size of the file. Note
> > @@ -722,8 +721,7 @@ upper_size_to_lower_size(struct ecryptfs_crypt_stat *crypt_stat,
> >   *
> >   * Returns zero on success; non-zero otherwise
> >   */
> > -static int truncate_upper(struct dentry *dentry, struct iattr *ia,
> > -			  struct iattr *lower_ia)
> > +static int truncate_upper(struct dentry *dentry, struct iattr *lower_ia)
> >  {
> >  	struct inode *inode = d_inode(dentry);
> >  	struct ecryptfs_crypt_stat *crypt_stat;
> > @@ -733,7 +731,7 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
> >  	size_t num_zeros;
> >  	int rc;
> >  
> > -	if (unlikely((ia->ia_size == i_size))) {
> > +	if (unlikely(lower_ia->ia_size == i_size)) {
> >  		lower_ia->ia_valid &= ~ATTR_SIZE;
> >  		return 0;
> >  	}
> > @@ -742,7 +740,7 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
> >  	if (rc)
> >  		return rc;
> >  
> > -	if (ia->ia_size > i_size) {
> > +	if (lower_ia->ia_size > i_size) {
> >  		char zero[] = { 0x00 };
> >  
> >  		/*
> > @@ -751,16 +749,14 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
> >  		 * intermediate portion of the previous end of the file and the
> >  		 * new and of the file.
> >  		 */
> > -		rc = ecryptfs_write(inode, zero, ia->ia_size - 1, 1);
> > +		rc = ecryptfs_write(inode, zero, lower_ia->ia_size - 1, 1);
> >  		lower_ia->ia_valid &= ~ATTR_SIZE;
> >  		goto out;
> >  	}
> >  
> >  	crypt_stat = &ecryptfs_inode_to_private(d_inode(dentry))->crypt_stat;
> >  	if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
> > -		truncate_setsize(inode, ia->ia_size);
> > -		lower_ia->ia_size = ia->ia_size;
> > -		lower_ia->ia_valid |= ATTR_SIZE;
> > +		truncate_setsize(inode, lower_ia->ia_size);
> >  		goto out;
> >  	}
> >  
> > @@ -769,17 +765,17 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
> >  	 * ia->ia_size is located. Fill in the end of that page from
> >  	 * (ia->ia_size & ~PAGE_MASK) to PAGE_SIZE with zeros.
> >  	 */
> > -	num_zeros = PAGE_SIZE - (ia->ia_size & ~PAGE_MASK);
> > +	num_zeros = PAGE_SIZE - (lower_ia->ia_size & ~PAGE_MASK);
> >  	if (num_zeros) {
> >  		rc = ecryptfs_write(inode, page_address(ZERO_PAGE(0)),
> > -				ia->ia_size, num_zeros);
> > +				lower_ia->ia_size, num_zeros);
> >  		if (rc) {
> >  			pr_err("Error attempting to zero out the remainder of the end page on reducing truncate; rc = [%d]\n",
> >  				rc);
> >  			goto out;
> >  		}
> >  	}
> > -	truncate_setsize(inode, ia->ia_size);
> > +	truncate_setsize(inode, lower_ia->ia_size);
> >  	rc = ecryptfs_write_inode_size_to_metadata(inode);
> >  	if (rc) {
> >  		pr_err("Problem with ecryptfs_write_inode_size_to_metadata; rc = [%d]\n",
> > @@ -794,13 +790,12 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
> >  	lower_size_before_truncate =
> >  		upper_size_to_lower_size(crypt_stat, i_size);
> >  	lower_size_after_truncate =
> > -		upper_size_to_lower_size(crypt_stat, ia->ia_size);
> > -	if (lower_size_after_truncate < lower_size_before_truncate) {
> > +		upper_size_to_lower_size(crypt_stat, lower_ia->ia_size);
> > +	if (lower_size_after_truncate < lower_size_before_truncate)
> >  		lower_ia->ia_size = lower_size_after_truncate;
> > -		lower_ia->ia_valid |= ATTR_SIZE;
> > -	} else {
> > +	else
> >  		lower_ia->ia_valid &= ~ATTR_SIZE;
> > -	}
> > +
> >  out:
> >  	ecryptfs_put_lower_file(inode);
> >  	return rc;
> > @@ -840,15 +835,17 @@ static int ecryptfs_inode_newsize_ok(struct inode *inode, loff_t offset)
> >   */
> >  int ecryptfs_truncate(struct dentry *dentry, loff_t new_length)
> >  {
> > -	struct iattr ia = { .ia_valid = ATTR_SIZE, .ia_size = new_length };
> > -	struct iattr lower_ia = { .ia_valid = 0 };
> > +	struct iattr lower_ia = {
> > +		.ia_valid	= ATTR_SIZE,
> > +		.ia_size	= new_length,
> > +	};
> >  	int rc;
> >  
> >  	rc = ecryptfs_inode_newsize_ok(d_inode(dentry), new_length);
> >  	if (rc)
> >  		return rc;
> >  
> > -	rc = truncate_upper(dentry, &ia, &lower_ia);
> > +	rc = truncate_upper(dentry, &lower_ia);
> >  	if (!rc && lower_ia.ia_valid & ATTR_SIZE) {
> >  		struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
> >  
> > @@ -943,7 +940,7 @@ static int ecryptfs_setattr(struct mnt_idmap *idmap,
> >  		if (rc)
> >  			goto out;
> >  
> > -		rc = truncate_upper(dentry, ia, &lower_ia);
> > +		rc = truncate_upper(dentry, &lower_ia);
> >  		if (rc < 0)
> >  			goto out;
> >  	}
> > -- 
> > 2.47.3
> > 
>