classes/reproducible_build: Use atomic rename for SDE file

If an existing source date epoch file was found during do_unpack, it was
deleted and a new one would be written in its place. This causes a race
with check-before-use code in get_source_date_epoch_value. Resolve the
problem by making do_unpack write the new source date epoch to a
temporary file, then do an atomic rename to ensure it's always present,
and change the check-before-use code to use a EAFP exception instead of
checking for file existence.

[YOCTO #14384]

(From OE-Core rev: b98d37da1554f524bd5b16287731d7b34945e92d)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 0b5e3b33187bf78a2d62cc886463e4b27d6bd228)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/meta/classes/reproducible_build.bbclass b/meta/classes/reproducible_build.bbclass
index 43cf9dc894..62655c2a5b 100644
--- a/meta/classes/reproducible_build.bbclass
+++ b/meta/classes/reproducible_build.bbclass
@@ -77,17 +77,16 @@ python create_source_date_epoch_stamp() {
     import oe.reproducible
 
     epochfile = d.getVar('SDE_FILE')
-    # If it exists we need to regenerate as the sources may have changed
-    if os.path.isfile(epochfile):
-        bb.debug(1, "Deleting existing SOURCE_DATE_EPOCH from: %s" % epochfile)
-        os.remove(epochfile)
+    tmp_file = "%s.new" % epochfile
 
     source_date_epoch = oe.reproducible.get_source_date_epoch(d, d.getVar('S'))
 
     bb.debug(1, "SOURCE_DATE_EPOCH: %d" % source_date_epoch)
     bb.utils.mkdirhier(d.getVar('SDE_DIR'))
-    with open(epochfile, 'w') as f:
+    with open(tmp_file, 'w') as f:
         f.write(str(source_date_epoch))
+
+    os.rename(tmp_file, epochfile)
 }
 
 def get_source_date_epoch_value(d):
@@ -100,7 +99,7 @@ def get_source_date_epoch_value(d):
         bb.debug(1, "Epoch file changed from %s to %s" % (efile, epochfile))
 
     source_date_epoch = int(d.getVar('SOURCE_DATE_EPOCH_FALLBACK'))
-    if os.path.isfile(epochfile):
+    try:
         with open(epochfile, 'r') as f:
             s = f.read()
             try:
@@ -113,7 +112,7 @@ def get_source_date_epoch_value(d):
                 bb.warn("SOURCE_DATE_EPOCH value '%s' is invalid. Reverting to SOURCE_DATE_EPOCH_FALLBACK" % s)
                 source_date_epoch = int(d.getVar('SOURCE_DATE_EPOCH_FALLBACK'))
         bb.debug(1, "SOURCE_DATE_EPOCH: %d" % source_date_epoch)
-    else:
+    except FileNotFoundError:
         bb.debug(1, "Cannot find %s. SOURCE_DATE_EPOCH will default to %d" % (epochfile, source_date_epoch))
 
     d.setVar('__CACHED_SOURCE_DATE_EPOCH', (str(source_date_epoch), epochfile))