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s3:smbd: fix NULL dereference in case of readlink failure

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When VFS readlinkat hook returns with error the following sequence
yields NULL-pointer dereference (SIGSEGV):

  symlink_target_below_conn (source3/smbd/open.c)
    char *target = NULL;
    ...
    readlink_talloc (source3/smbd/files.c)
      SMB_VFS_READLINKAT
        smb_vfs_call_readlinkat (source3/smbd/vfs.c)
          handle->fns->readlinkat_fn --> returns error

  status = safe_symlink_target_path(.., target /* NULL */ ..)
    safe_symlink_target_path (source3/smbd/filename.c)
      if (target[0] == '/') { /* NULL pointer dereference */

A failure in VFS module's readlinkat hook may happen due to run-time
error (e.g., network failure which cases libcephfs to disconnect from
MDS).

Bug: https://bugzilla.samba.org/show_bug.cgi?id=15700
Signed-off-by: Shachar Sharon <ssharon@redhat.com>
Reviewed-by: John Mulligan <jmulligan@redhat.com>
Reviewed-by: Volker Lendecke <vl@samba.org>

Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Fri Aug 23 09:27:06 UTC 2024 on atb-devel-224

(cherry picked from commit 168966a053045476a84044aa73f66722eb702fe0)

Autobuild-User(v4-21-test): Jule Anger <janger@samba.org>
Autobuild-Date(v4-21-test): Mon Aug 26 11:09:31 UTC 2024 on atb-devel-224
This commit is contained in:
Shachar Sharon 2024-08-22 14:44:28 +03:00 committed by Jule Anger
parent 0d41094f13
commit 37bbe0ca09
1 changed files with 4 additions and 0 deletions
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4
source3/smbd/open.c
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@ -582,6 +582,10 @@ static NTSTATUS symlink_target_below_conn(
talloc_tos(), dirfsp, symlink_name, &target);
}
if (!NT_STATUS_IS_OK(status)) {
return status;
}
status = safe_symlink_target_path(talloc_tos(),
connection_path,
dirfsp->fsp_name->base_name,