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s3:smbd: let mkdir_internal() try VFS_RENAME_HOW_NO_REPLACE first

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With renameat2(RENAME_NOREPLACE) being available
it's even better, as we don't even have the short
window where the incomplete directory is visible
to others.

The flow will be this:

tmp_name = ".::TMPNAME:D:$PID:client_name"
mkdirat(tmp_name, mode=client_mode);
prepare_acls(tmp_name);
renameat2(tmp_name, client_name, NOREPLACE);
if (EEXIST) {
   unlinkat(tmp_name);
   return EEXIST;
}
if (EINVAL) {
   /* fallback if NOREPLACE is not supported */
   mkdirat(client_name, mode=0);
   if (EEXIST) {
      unlinkat(tmp_name);
      return EEXIST;
   }
   renameat(tmp_name, client_name);
}

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15693

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This commit is contained in:
Stefan Metzmacher 2024-08-07 17:01:53 +02:00
parent fe8b4617dd
commit 1bacaae526
1 changed files with 24 additions and 2 deletions
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26
source3/smbd/open.c
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@ -4681,7 +4681,7 @@ static NTSTATUS mkdir_internal(connection_struct *conn,
struct server_id_buf idbuf;
char *idstr = server_id_str_buf_unique_ex(id, '%', &idbuf);
struct vfs_open_how how = { .flags = O_RDONLY|O_DIRECTORY, };
struct vfs_rename_how rhow = { .flags = 0, };
struct vfs_rename_how rhow = { .flags = VFS_RENAME_HOW_NO_REPLACE, };
int ret;
if (!CAN_WRITE(conn) || (access_mask & ~(conn->share_access))) {
@ -4896,7 +4896,27 @@ mkdir_first:
*/
tmp_atname->st = smb_dname->st;
{
/*
* We first try VFS_RENAME_HOW_NO_REPLACE,
* if it's implemented in the kernel,
* we'll always get EEXIST if the target
* exist, as it's handled at the linux vfs
* layer. But if it doesn't exist we
* can still get EINVAL if the actual
* filesystem doesn't support RENAME_NOREPLACE.
*
* If the kernel doesn't support rename2()
* we get EINVAL instead of ENOSYS (this
* is mapped in the libreplace replacement
* (as well as the glibc replacement).
*/
ret = SMB_VFS_RENAMEAT(conn,
parent_dir_fname->fsp,
tmp_atname,
parent_dir_fname->fsp,
smb_fname_atname,
&rhow);
if (ret == -1 && errno == EINVAL) {
/*
* This is the strategie we use without having
* renameat2(RENAME_NOREPLACE):
@ -4916,6 +4936,8 @@ mkdir_first:
* the incomplete directory, which has a mode of 0.
*/
rhow.flags &= ~VFS_RENAME_HOW_NO_REPLACE;
DBG_DEBUG("MKDIRAT/RENAMEAT '%s' -> '%s'\n",
tmp_dname, orig_dname);