From cc57232cae23c0df91b4a59d0f519141ce9b5b02 Mon Sep 17 00:00:00 2001 From: Sean Shen Date: Tue, 26 May 2026 22:07:16 +0900 Subject: [PATCH] ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE FSCTL_SET_SPARSE in fsctl_set_sparse() modifies the file's sparse attribute and saves it through xattr without any permission checks. This exposes two issues: 1) A client on a read-only share can change the sparse attribute on files it opened, even though the share is read-only. Other FSCTL write operations already check test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE), but FSCTL_SET_SPARSE does not. 2) Even on writable shares, clients without FILE_WRITE_DATA or FILE_WRITE_ATTRIBUTES access should not modify the sparse attribute. Similar handle-level checks exist in other functions but are missing here. Add both share-level writable check and per-handle access check. Use goto out on error to avoid leaking file references. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: Namjae Jeon Cc: Sergey Senozhatsky Cc: Steve French Signed-off-by: Sean Shen Acked-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/smb2pdu.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index 5128a693aca6..620bcfbbfd92 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -8202,9 +8202,20 @@ static inline int fsctl_set_sparse(struct ksmbd_work *work, u64 id, int ret = 0; __le32 old_fattr; + if (!test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE)) { + ksmbd_debug(SMB, "User does not have write permission\n"); + return -EACCES; + } + fp = ksmbd_lookup_fd_fast(work, id); if (!fp) return -ENOENT; + + if (!(fp->daccess & (FILE_WRITE_DATA_LE | FILE_WRITE_ATTRIBUTES_LE))) { + ret = -EACCES; + goto out; + } + idmap = file_mnt_idmap(fp->filp); old_fattr = fp->f_ci->m_fattr;