From 4fc4efeb6afd9dcf2661df8a5b01ee1dc112d822 Mon Sep 17 00:00:00 2001
From: Jeremy Allison <jra@samba.org>
Date: Wed, 5 Jan 2022 11:40:46 -0800
Subject: [PATCH] s3: smbd: Create and use a common function for generating a
 fileid - create_clock_itime().

This first gets the clock_gettime_mono() value, converts to an NTTIME (as
this is what is stored in the dos attribute EA), then mixes in 8 bits of
randomness shifted up by 55 bits to cope with poor resolution clocks to
avoid duplicate inodes.

Using 8 bits of randomness on top of an NTTIME gives us around 114
years headroom.

The top bit is then set to avoid collisions with system inode
numbers.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14928

Signed-off-by: Jeremy Allison <jra@samba.org>
---
 source3/include/proto.h |  1 +
 source3/lib/system.c    | 43 +++++++++++++++++++++++++++++++++++++++++
 source3/smbd/open.c     |  6 +++---
 3 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/source3/include/proto.h b/source3/include/proto.h
index 6154b1ab26d..dba728b3d86 100644
--- a/source3/include/proto.h
+++ b/source3/include/proto.h
@@ -175,6 +175,7 @@ void update_stat_ex_create_time(struct stat_ex *dst, struct timespec create_time
 void update_stat_ex_file_id(struct stat_ex *dst, uint64_t file_id);
 void update_stat_ex_from_saved_stat(struct stat_ex *dst,
 				    const struct stat_ex *src);
+void create_clock_itime(struct stat_ex *dst);
 int sys_stat(const char *fname, SMB_STRUCT_STAT *sbuf,
 	     bool fake_dir_create_times);
 int sys_fstat(int fd, SMB_STRUCT_STAT *sbuf,
diff --git a/source3/lib/system.c b/source3/lib/system.c
index 671fc2760a0..9f62748a3f7 100644
--- a/source3/lib/system.c
+++ b/source3/lib/system.c
@@ -310,6 +310,49 @@ void init_stat_ex_from_stat (struct stat_ex *dst,
 	dst->st_ex_iflags |= ST_EX_IFLAG_CALCULATED_FILE_ID;
 }
 
+/*******************************************************************
+ Create a clock-derived itime (imaginary) birthtime.
+********************************************************************/
+
+void create_clock_itime(struct stat_ex *dst)
+{
+	NTTIME tval;
+	struct timespec itime;
+	uint64_t mixin;
+	uint8_t rval;
+
+	/* Start with the system clock. */
+	clock_gettime_mono(&itime);
+
+	/* Convert to NTTIME. */
+	tval = unix_timespec_to_nt_time(itime);
+
+	/* Generate a random byte. */
+	generate_random_buffer((unsigned char *)&rval, 1);
+	mixin = rval;
+
+	/*
+	 * Shift up by 55 bits. This gives us 114 years
+	 * of headroom.
+	 */
+	mixin <<= 55;
+
+	/*
+	 * Set the top bit to differentiate this
+	 * from a system inode.
+	 */
+	mixin |= 0x8000000000000000LL;
+
+	/* And OR into the nttime. */
+	tval |= mixin;
+
+	/* Convert back to a timespec. */
+	itime = nt_time_to_full_timespec(tval);
+
+	/* And set as a generated itime. */
+	update_stat_ex_itime(dst, itime);
+}
+
 /*******************************************************************
 A stat() wrapper.
 ********************************************************************/
diff --git a/source3/smbd/open.c b/source3/smbd/open.c
index e3bb304292e..cf5c620fe21 100644
--- a/source3/smbd/open.c
+++ b/source3/smbd/open.c
@@ -4129,13 +4129,13 @@ static NTSTATUS open_file_ntcreate(connection_struct *conn,
 	 * If we created a file and it's not a stream, this is the point where
 	 * we set the itime (aka invented time) that get's stored in the DOS
 	 * attribute xattr. The value is going to be either what the filesystem
-	 * provided or a copy of the creation date.
+	 * provided or a generated itime value.
 	 *
 	 * Either way, we turn the itime into a File-ID, unless the filesystem
 	 * provided one (unlikely).
 	 */
 	if (info == FILE_WAS_CREATED && !is_named_stream(smb_fname)) {
-		smb_fname->st.st_ex_iflags &= ~ST_EX_IFLAG_CALCULATED_ITIME;
+		create_clock_itime(&smb_fname->st);
 
 		if (lp_store_dos_attributes(SNUM(conn)) &&
 		    smb_fname->st.st_ex_iflags & ST_EX_IFLAG_CALCULATED_FILE_ID)
@@ -4317,7 +4317,7 @@ static NTSTATUS mkdir_internal(connection_struct *conn,
 		return NT_STATUS_NOT_A_DIRECTORY;
 	}
 
-	smb_dname->st.st_ex_iflags &= ~ST_EX_IFLAG_CALCULATED_ITIME;
+	create_clock_itime(&smb_dname->st);
 
 	if (lp_store_dos_attributes(SNUM(conn))) {
 		if (smb_dname->st.st_ex_iflags & ST_EX_IFLAG_CALCULATED_FILE_ID)
-- 
2.30.2