From a8603b52b39f520ea8a34def74c23fba87396d3e Mon Sep 17 00:00:00 2001 From: Paulo Alcantara Date: Fri, 28 Aug 2026 19:08:09 -0300 Subject: [PATCH] smb: client: fix data corruption with concurrent writes and O_TRUNC cifs_do_truncate() flushes dirty pages with filemap_write_and_wait() and truncates the file on the server, but in the old code both operations ran without holding i_rwsem or invalidate_lock. A concurrent buffered write via netfs_perform_write() -- which only needs i_rwsem shared -- could dirty new pages after the flush but before the local truncation, and those pages would be silently discarded by cifs_setsize() -> truncate_pagecache(). Fix by acquiring inode_lock (exclusive i_rwsem) and filemap_invalidate_lock at the top of cifs_do_truncate(), so the entire flush-truncate-resize sequence is atomic with respect to: - buffered writes (blocked by exclusive i_rwsem, since netfs_start_io_write takes i_rwsem shared), - read page faults (blocked by exclusive invalidate_lock, since filemap_fault takes it shared), - writeback collection (blocked by netfs_wb_begin/netfs_wb_end around the server truncate and local resize, since netfs_writepages also acquires the wb lock). Fixes: 110fee6b9bb5 ("smb: client: fix missing timestamp updates with O_TRUNC") Signed-off-by: Paulo Alcantara Reviewed-by: Namjae Jeon Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: Bharath SM Cc: stable@vger.kernel.org --- fs/smb/client/file.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-) diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c index 100acc76e9be..61f9c6ccc6be 100644 --- a/fs/smb/client/file.c +++ b/fs/smb/client/file.c @@ -999,42 +999,50 @@ static int cifs_do_truncate(const unsigned int xid, struct dentry *dentry) struct cifs_tcon *tcon; int rc; - rc = filemap_write_and_wait(inode->i_mapping); - if (is_interrupt_error(rc)) + rc = inode_lock_killable(inode); + if (rc) return -ERESTARTSYS; + + filemap_invalidate_lock(inode->i_mapping); + + rc = filemap_write_and_wait(inode->i_mapping); + if (is_interrupt_error(rc)) { + rc = -ERESTARTSYS; + goto out; + } mapping_set_error(inode->i_mapping, rc); cfile = find_writable_file(cinode, FIND_FSUID_ONLY); rc = cifs_file_flush(xid, inode, cfile); if (!rc) { if (cfile) { + struct netfs_inode *ictx = netfs_inode(inode); + tcon = tlink_tcon(cfile->tlink); server = tcon->ses->server; + netfs_wb_begin(ictx, false); rc = server->ops->set_file_size(xid, tcon, cfile, 0, false); if (!rc) { - inode_lock(inode); - filemap_invalidate_lock(inode->i_mapping); netfs_resize_file(&cinode->netfs, 0, true); cifs_setsize(inode, 0); - filemap_invalidate_unlock(inode->i_mapping); - inode_unlock(inode); cifs_invalidate_cache(inode, 0); } + netfs_wb_end(ictx); } else { /* * No cached handle; evict stale pages so they can't * be served after the file is later extended; let * the server's O_TRUNC open response set the i_size */ - inode_lock(inode); - filemap_invalidate_lock(inode->i_mapping); truncate_inode_pages(inode->i_mapping, 0); - filemap_invalidate_unlock(inode->i_mapping); - inode_unlock(inode); cifs_invalidate_cache(inode, 0); } } + +out: + filemap_invalidate_unlock(inode->i_mapping); + inode_unlock(inode); if (cfile) cifsFileInfo_put(cfile); return rc;