netfs: Fix potential for tearing in ->remote_i_size and ->zero_point

Fix potential tearing in using ->remote_i_size and ->zero_point by copying
i_size_read() and i_size_write() and using the same seqcount as for i_size.

We need to make sure that netfslib and the filesystems that use it always
hold i_lock whilst updating any of the sizes to prevent i_size_seqcount
from getting corrupted.

Fixes: 4058f742105e ("netfs: Keep track of the actual remote file size")
Fixes: 100ccd18bb41 ("netfs: Optimise away reads above the point at which there can be no data")
Closes: https://sashiko.dev/#/patchset/20260414082004.3756080-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260512123404.719402-6-dhowells@redhat.com
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

7 files changed, 74 insertions, 42 deletions

diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 9f76b0347fa9..feac491c5070 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -434,7 +434,8 @@ cifs_alloc_inode(struct super_block *sb)
 	spin_lock_init(&cifs_inode->writers_lock);
 	cifs_inode->writers = 0;
 	cifs_inode->netfs.inode.i_blkbits = 14;  /* 2**14 = CIFS_MAX_MSGSIZE */
-	cifs_inode->netfs.remote_i_size = 0;
+	cifs_inode->netfs._remote_i_size = 0;
+	cifs_inode->netfs._zero_point = 0;
 	cifs_inode->uniqueid = 0;
 	cifs_inode->createtime = 0;
 	cifs_inode->epoch = 0;
@@ -1303,7 +1304,8 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 	struct cifsFileInfo *smb_file_src = src_file->private_data;
 	struct cifsFileInfo *smb_file_target = dst_file->private_data;
 	struct cifs_tcon *target_tcon, *src_tcon;
-	unsigned long long destend, fstart, fend, old_size, new_size;
+	unsigned long long i_size, old_size, new_size, zero_point;
+	unsigned long long destend, fstart, fend;
 	unsigned int xid;
 	int rc;
 
@@ -1347,7 +1349,7 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 	 * Advance the EOF marker after the flush above to the end of the range
 	 * if it's short of that.
 	 */
-	if (src_cifsi->netfs.remote_i_size < off + len) {
+	if (netfs_read_remote_i_size(src_inode) < off + len) {
 		rc = cifs_precopy_set_eof(src_inode, src_cifsi, src_tcon, xid, off + len);
 		if (rc < 0)
 			goto unlock;
@@ -1368,16 +1370,18 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 	rc = cifs_flush_folio(target_inode, destend, &fstart, &fend, false);
 	if (rc)
 		goto unlock;
-	if (fend > target_cifsi->netfs.zero_point)
-		target_cifsi->netfs.zero_point = fend + 1;
-	old_size = target_cifsi->netfs.remote_i_size;
+
+	spin_lock(&target_inode->i_lock);
+	if (fend > zero_point)
+		netfs_write_zero_point(target_inode, fend + 1);
+	i_size = target_inode->i_size;
+	spin_unlock(&target_inode->i_lock);
 
 	/* Discard all the folios that overlap the destination region. */
 	cifs_dbg(FYI, "about to discard pages %llx-%llx\n", fstart, fend);
 	truncate_inode_pages_range(&target_inode->i_data, fstart, fend);
 
-	fscache_invalidate(cifs_inode_cookie(target_inode), NULL,
-			   i_size_read(target_inode), 0);
+	fscache_invalidate(cifs_inode_cookie(target_inode), NULL, i_size, 0);
 
 	rc = -EOPNOTSUPP;
 	if (target_tcon->ses->server->ops->duplicate_extents) {
@@ -1402,8 +1406,12 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 					rc = -EINVAL;
 			}
 		}
-		if (rc == 0 && new_size > target_cifsi->netfs.zero_point)
-			target_cifsi->netfs.zero_point = new_size;
+		if (rc == 0) {
+			spin_lock(&target_inode->i_lock);
+			if (new_size > target_cifsi->netfs._zero_point)
+				netfs_write_zero_point(target_inode, new_size);
+			spin_unlock(&target_inode->i_lock);
+		}
 	}
 
 	/* force revalidate of size and timestamps of target file now
@@ -1474,7 +1482,7 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
 	 * Advance the EOF marker after the flush above to the end of the range
 	 * if it's short of that.
 	 */
-	if (src_cifsi->netfs.remote_i_size < off + len) {
+	if (netfs_read_remote_i_size(src_inode) < off + len) {
 		rc = cifs_precopy_set_eof(src_inode, src_cifsi, src_tcon, xid, off + len);
 		if (rc < 0)
 			goto unlock;
@@ -1502,8 +1510,12 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
 			fscache_resize_cookie(cifs_inode_cookie(target_inode),
 					      i_size_read(target_inode));
 		}
-		if (rc > 0 && destoff + rc > target_cifsi->netfs.zero_point)
-			target_cifsi->netfs.zero_point = destoff + rc;
+		if (rc > 0) {
+			spin_lock(&target_inode->i_lock);
+			if (destoff + rc > target_cifsi->netfs._zero_point)
+				netfs_write_zero_point(target_inode, destoff + rc);
+			spin_unlock(&target_inode->i_lock);
+		}
 	}
 
 	file_accessed(src_file);
diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index 3990a9012264..9e27bfa7376b 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1465,6 +1465,7 @@ cifs_readv_callback(struct TCP_Server_Info *server, struct mid_q_entry *mid)
 	struct cifs_io_subrequest *rdata = mid->callback_data;
 	struct netfs_inode *ictx = netfs_inode(rdata->rreq->inode);
 	struct cifs_tcon *tcon = tlink_tcon(rdata->req->cfile->tlink);
+	struct inode *inode = &ictx->inode;
 	struct smb_rqst rqst = { .rq_iov = rdata->iov,
 				 .rq_nvec = 1,
 				 .rq_iter = rdata->subreq.io_iter };
@@ -1538,7 +1539,7 @@ do_retry:
 	} else {
 		size_t trans = rdata->subreq.transferred + rdata->got_bytes;
 		if (trans < rdata->subreq.len &&
-		    rdata->subreq.start + trans >= ictx->remote_i_size) {
+		    rdata->subreq.start + trans >= netfs_read_remote_i_size(inode)) {
 			rdata->result = 0;
 			__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
 		} else if (rdata->got_bytes > 0) {
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 664a2c223089..b60344125f27 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -2517,18 +2517,23 @@ int cifs_lock(struct file *file, int cmd, struct file_lock *flock)
 void cifs_write_subrequest_terminated(struct cifs_io_subrequest *wdata, ssize_t result)
 {
 	struct netfs_io_request *wreq = wdata->rreq;
-	struct netfs_inode *ictx = netfs_inode(wreq->inode);
+	struct inode *inode = wreq->inode;
+	struct netfs_inode *ictx = netfs_inode(inode);
 	loff_t wrend;
 
 	if (result > 0) {
+		spin_lock(&inode->i_lock);
+
 		wrend = wdata->subreq.start + wdata->subreq.transferred + result;
 
-		if (wrend > ictx->zero_point &&
+		if (wrend > ictx->_zero_point &&
 		    (wdata->rreq->origin == NETFS_UNBUFFERED_WRITE ||
 		     wdata->rreq->origin == NETFS_DIO_WRITE))
-			ictx->zero_point = wrend;
-		if (wrend > ictx->remote_i_size)
+			netfs_write_zero_point(inode, wrend);
+		if (wrend > ictx->_remote_i_size)
 			netfs_resize_file(ictx, wrend, true);
+
+		spin_unlock(&inode->i_lock);
 	}
 
 	netfs_write_subrequest_terminated(&wdata->subreq, result);
diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index 16a5310155d5..9472c0a6c187 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -119,7 +119,7 @@ cifs_revalidate_cache(struct inode *inode, struct cifs_fattr *fattr)
 	fattr->cf_mtime = timestamp_truncate(fattr->cf_mtime, inode);
 	mtime = inode_get_mtime(inode);
 	if (timespec64_equal(&mtime, &fattr->cf_mtime) &&
-	    cifs_i->netfs.remote_i_size == fattr->cf_eof) {
+	    netfs_read_remote_i_size(inode) == fattr->cf_eof) {
 		cifs_dbg(FYI, "%s: inode %llu is unchanged\n",
 			 __func__, cifs_i->uniqueid);
 		return;
@@ -173,12 +173,12 @@ cifs_fattr_to_inode(struct inode *inode, struct cifs_fattr *fattr,
 		CIFS_I(inode)->time = 0; /* force reval */
 		return -ESTALE;
 	}
-	if (inode_state_read_once(inode) & I_NEW)
-		CIFS_I(inode)->netfs.zero_point = fattr->cf_eof;
-
 	cifs_revalidate_cache(inode, fattr);
 
 	spin_lock(&inode->i_lock);
+	if (inode_state_read_once(inode) & I_NEW)
+		netfs_write_zero_point(inode, fattr->cf_eof);
+
 	fattr->cf_mtime = timestamp_truncate(fattr->cf_mtime, inode);
 	fattr->cf_atime = timestamp_truncate(fattr->cf_atime, inode);
 	fattr->cf_ctime = timestamp_truncate(fattr->cf_ctime, inode);
@@ -212,7 +212,7 @@ cifs_fattr_to_inode(struct inode *inode, struct cifs_fattr *fattr,
 	else
 		clear_bit(CIFS_INO_DELETE_PENDING, &cifs_i->flags);
 
-	cifs_i->netfs.remote_i_size = fattr->cf_eof;
+	netfs_write_remote_i_size(inode, fattr->cf_eof);
 	/*
 	 * Can't safely change the file size here if the client is writing to
 	 * it due to potential races.
@@ -2772,7 +2772,9 @@ cifs_revalidate_mapping(struct inode *inode)
 		if (cifs_sb_flags(cifs_sb) & CIFS_MOUNT_RW_CACHE)
 			goto skip_invalidate;
 
-		cifs_inode->netfs.zero_point = cifs_inode->netfs.remote_i_size;
+		spin_lock(&inode->i_lock);
+		netfs_write_zero_point(inode, netfs_inode(inode)->_remote_i_size);
+		spin_unlock(&inode->i_lock);
 		rc = filemap_invalidate_inode(inode, true, 0, LLONG_MAX);
 		if (rc) {
 			cifs_dbg(VFS, "%s: invalidate inode %p failed with rc %d\n",
diff --git a/fs/smb/client/readdir.c b/fs/smb/client/readdir.c
index be22bbc4a65a..e860fa08b5e3 100644
--- a/fs/smb/client/readdir.c
+++ b/fs/smb/client/readdir.c
@@ -143,7 +143,8 @@ retry:
 						fattr->cf_rdev = inode->i_rdev;
 						fattr->cf_uid = inode->i_uid;
 						fattr->cf_gid = inode->i_gid;
-						fattr->cf_eof = CIFS_I(inode)->netfs.remote_i_size;
+						fattr->cf_eof =
+							netfs_read_remote_i_size(inode);
 						fattr->cf_symlink_target = NULL;
 					} else {
 						CIFS_I(inode)->time = 0;
diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index e6cb9b144530..0ea3ce1b94ea 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3402,8 +3402,7 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 	struct inode *inode = file_inode(file);
 	struct cifsInodeInfo *cifsi = CIFS_I(inode);
 	struct cifsFileInfo *cfile = file->private_data;
-	struct netfs_inode *ictx = netfs_inode(inode);
-	unsigned long long i_size, new_size, remote_size;
+	unsigned long long i_size, new_size, remote_i_size, zero_point;
 	long rc;
 	unsigned int xid;
 
@@ -3414,9 +3413,8 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 
 	filemap_invalidate_lock(inode->i_mapping);
 
-	i_size = i_size_read(inode);
-	remote_size = ictx->remote_i_size;
-	if (offset + len >= remote_size && offset < i_size) {
+	netfs_read_sizes(inode, &i_size, &remote_i_size, &zero_point);
+	if (offset + len >= remote_i_size && offset < i_size) {
 		unsigned long long top = umin(offset + len, i_size);
 
 		rc = filemap_write_and_wait_range(inode->i_mapping, offset, top - 1);
@@ -3449,9 +3447,11 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 				  cfile->fid.volatile_fid, cfile->pid, new_size);
 		if (rc >= 0) {
 			truncate_setsize(inode, new_size);
+			spin_lock(&inode->i_lock);
 			netfs_resize_file(&cifsi->netfs, new_size, true);
-			if (offset < cifsi->netfs.zero_point)
-				cifsi->netfs.zero_point = offset;
+			if (offset < cifsi->netfs._zero_point)
+				netfs_write_zero_point(inode, offset);
+			spin_unlock(&inode->i_lock);
 			fscache_resize_cookie(cifs_inode_cookie(inode), new_size);
 		}
 	}
@@ -3474,7 +3474,7 @@ static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 	struct inode *inode = file_inode(file);
 	struct cifsFileInfo *cfile = file->private_data;
 	struct file_zero_data_information fsctl_buf;
-	unsigned long long end = offset + len, i_size, remote_i_size;
+	unsigned long long end = offset + len, i_size, remote_i_size, zero_point;
 	long rc;
 	unsigned int xid;
 	__u8 set_sparse = 1;
@@ -3516,14 +3516,17 @@ static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 	 * that we locally hole-punch the tail of the dirty data, the proposed
 	 * EOF update will end up in the wrong place.
 	 */
-	i_size = i_size_read(inode);
-	remote_i_size = netfs_inode(inode)->remote_i_size;
+	netfs_read_sizes(inode, &i_size, &remote_i_size, &zero_point);
+
 	if (end > remote_i_size && i_size > remote_i_size) {
 		unsigned long long extend_to = umin(end, i_size);
 		rc = SMB2_set_eof(xid, tcon, cfile->fid.persistent_fid,
 				  cfile->fid.volatile_fid, cfile->pid, extend_to);
-		if (rc >= 0)
-			netfs_inode(inode)->remote_i_size = extend_to;
+		if (rc >= 0) {
+			spin_lock(&inode->i_lock);
+			netfs_write_remote_i_size(inode, extend_to);
+			spin_unlock(&inode->i_lock);
+		}
 	}
 
 unlock:
@@ -3787,7 +3790,6 @@ static long smb3_collapse_range(struct file *file, struct cifs_tcon *tcon,
 	struct inode *inode = file_inode(file);
 	struct cifsInodeInfo *cifsi = CIFS_I(inode);
 	struct cifsFileInfo *cfile = file->private_data;
-	struct netfs_inode *ictx = &cifsi->netfs;
 	loff_t old_eof, new_eof;
 
 	xid = get_xid();
@@ -3805,7 +3807,9 @@ static long smb3_collapse_range(struct file *file, struct cifs_tcon *tcon,
 		goto out_2;
 
 	truncate_pagecache_range(inode, off, old_eof);
-	ictx->zero_point = old_eof;
+	spin_lock(&inode->i_lock);
+	netfs_write_zero_point(inode, old_eof);
+	spin_unlock(&inode->i_lock);
 	netfs_wait_for_outstanding_io(inode);
 
 	rc = smb2_copychunk_range(xid, cfile, cfile, off + len,
@@ -3822,8 +3826,10 @@ static long smb3_collapse_range(struct file *file, struct cifs_tcon *tcon,
 	rc = 0;
 
 	truncate_setsize(inode, new_eof);
+	spin_lock(&inode->i_lock);
 	netfs_resize_file(&cifsi->netfs, new_eof, true);
-	ictx->zero_point = new_eof;
+	netfs_write_zero_point(inode, new_eof);
+	spin_unlock(&inode->i_lock);
 	fscache_resize_cookie(cifs_inode_cookie(inode), new_eof);
 out_2:
 	filemap_invalidate_unlock(inode->i_mapping);
@@ -3866,13 +3872,17 @@ static long smb3_insert_range(struct file *file, struct cifs_tcon *tcon,
 		goto out_2;
 
 	truncate_setsize(inode, new_eof);
+	spin_lock(&inode->i_lock);
 	netfs_resize_file(&cifsi->netfs, i_size_read(inode), true);
+	spin_unlock(&inode->i_lock);
 	fscache_resize_cookie(cifs_inode_cookie(inode), i_size_read(inode));
 
 	rc = smb2_copychunk_range(xid, cfile, cfile, off, count, off + len);
 	if (rc < 0)
 		goto out_2;
-	cifsi->netfs.zero_point = new_eof;
+	spin_lock(&inode->i_lock);
+	netfs_write_zero_point(inode, new_eof);
+	spin_unlock(&inode->i_lock);
 
 	rc = smb3_zero_data(file, tcon, off, len, xid);
 	if (rc < 0)
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 995fcdd30681..3bd300347f16 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -4608,6 +4608,7 @@ smb2_readv_callback(struct TCP_Server_Info *server, struct mid_q_entry *mid)
 	struct netfs_inode *ictx = netfs_inode(rdata->rreq->inode);
 	struct cifs_tcon *tcon = tlink_tcon(rdata->req->cfile->tlink);
 	struct smb2_hdr *shdr = (struct smb2_hdr *)rdata->iov[0].iov_base;
+	struct inode *inode = &ictx->inode;
 	struct cifs_credits credits = {
 		.value = 0,
 		.instance = 0,
@@ -4721,7 +4722,7 @@ do_retry:
 	} else {
 		size_t trans = rdata->subreq.transferred + rdata->got_bytes;
 		if (trans < rdata->subreq.len &&
-		    rdata->subreq.start + trans >= ictx->remote_i_size) {
+		    rdata->subreq.start + trans >= netfs_read_remote_i_size(inode)) {
 			__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
 			rdata->result = 0;
 		}