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ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

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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: e2f34481b2 ("cifsd: add server-side procedures for SMB3")
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steve French <smfrench@gmail.com>
Signed-off-by: Sean Shen <grayhat@foxmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Sean Shen 2026-05-26 22:07:16 +09:00 committed by Steve French
parent 2f15dcd0d4
commit cc57232cae
1 changed files with 11 additions and 0 deletions
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11
fs/smb/server/smb2pdu.c
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@ -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;