Public bug reported:
[Impact]
If you set Dir::Cache or Dir::Cache::pkgcache to /dev/null, /dev/null is
chmodded as we chmod the cache file to 666. This is a semi-common pattern to
not use a cache, and breaks user scripts.
[Test plan]
1. autopkgtests run the large integration test suite
2. run manually
apt-cache gencaches -o Dir::Cache::pkgcache=/dev/null
apt-cache gencaches -o Dir::Cache::srcpkgcache=/dev/null
apt-cache gencaches -o Dir::Cache=/dev/null
and observe that /dev/null is still correct.
[Where problems could occur]
We have eliminated writing the cache to /dev/null entirely:
--- a/apt-pkg/pkgcachegen.cc
+++ b/apt-pkg/pkgcachegen.cc
@@ -1637,6 +1637,10 @@ static DynamicMMap* CreateDynamicMMap(FileFd * const
CacheF, unsigned long Flags
static bool writeBackMMapToFile(pkgCacheGenerator * const Gen, DynamicMMap *
const Map,
std::string const &FileName)
{
+ // Do not write the file back to /dev/null or try to change its mode...
+ if (FileName == "/dev/null")
+ return true;
It's possible we may introduce issues later because something in there
does fancy bits and the cache in memory becomes invalid, but so far I
only saw that we calculate the hash in there, but we set dirty
afterwards and don't actually use the cache hash if we don't load from
disk so I think in reality this is not a problem, at least now. Just
gotta be careful to not stuff anything other than writing in there.
** Affects: apt (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2067138
Title:
Dir::Cache=/dev/null chmods /dev/null
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