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daemon: Address shortcoming in previous security fix for CVE-2024-27297. 

This is a followup to 8f4ffb3fae.

Commit 8f4ffb3fae fell short in two
ways: (1) it didn’t have any effet for fixed-output derivations
performed in a chroot, which is the case for all of them except those
using “builtin:download” and “builtin:git-download”, and (2) it did not
preserve ownership when copying, leading to “suspicious ownership or
permission […] rejecting this build output” errors.

* nix/libstore/build.cc (DerivationGoal::buildDone): Account for
‘chrootRootDir’ when copying ‘drv.outputs’.
* nix/libutil/util.cc (copyFileRecursively): Add ‘fchown’ and ‘fchownat’
calls to preserve file ownership; this is necessary for chrooted
fixed-output derivation builds.
* nix/libutil/util.hh: Update comment.

Change-Id: Ib59f040e98fed59d1af81d724b874b592cbef156
This commit is contained in:
Ludovic Courtès 2024-03-12 11:53:35 +01:00
parent fc1762fe38
commit ff1251de0b
No known key found for this signature in database
GPG Key ID: 090B11993D9AEBB5
3 changed files with 14 additions and 8 deletions
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11
nix/libstore/build.cc
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@ -1387,13 +1387,14 @@ void DerivationGoal::buildDone()
make sure that there's no stale file descriptor pointing to it
(CVE-2024-27297). */
foreach (DerivationOutputs::iterator, i, drv.outputs) {
if (pathExists(i->second.path)) {
Path pivot = i->second.path + ".tmp";
copyFileRecursively(i->second.path, pivot, true);
int err = rename(pivot.c_str(), i->second.path.c_str());
Path output = chrootRootDir + i->second.path;
if (pathExists(output)) {
Path pivot = output + ".tmp";
copyFileRecursively(output, pivot, true);
int err = rename(pivot.c_str(), output.c_str());
if (err != 0)
throw SysError(format("renaming `%1%' to `%2%'")
% pivot % i->second.path);
% pivot % output);
}
}
}

4
nix/libutil/util.cc
View File

@ -422,6 +422,7 @@ static void copyFileRecursively(int sourceroot, const Path &source,
if (destinationFd == -1) throw SysError(format("opening `%1%'") % source);
copyFile(sourceFd, destinationFd);
fchown(destinationFd, st.st_uid, st.st_gid);
} else if (S_ISLNK(st.st_mode)) {
char target[st.st_size + 1];
ssize_t result = readlinkat(sourceroot, source.c_str(), target, st.st_size);
@ -430,6 +431,8 @@ static void copyFileRecursively(int sourceroot, const Path &source,
int err = symlinkat(target, destinationroot, destination.c_str());
if (err != 0)
throw SysError(format("creating symlink `%1%'") % destination);
fchownat(destinationroot, destination.c_str(),
st.st_uid, st.st_gid, AT_SYMLINK_NOFOLLOW);
} else if (S_ISDIR(st.st_mode)) {
int err = mkdirat(destinationroot, destination.c_str(), 0755);
if (err != 0)
@ -455,6 +458,7 @@ static void copyFileRecursively(int sourceroot, const Path &source,
for (auto & i : readDirectory(sourceFd))
copyFileRecursively((int)sourceFd, i.name, (int)destinationFd, i.name,
deleteSource);
fchown(destinationFd, st.st_uid, st.st_gid);
} else throw Error(format("refusing to copy irregular file `%1%'") % source);
if (deleteSource)

7
nix/libutil/util.hh
View File

@ -102,9 +102,10 @@ void deletePath(const Path & path);
void deletePath(const Path & path, unsigned long long & bytesFreed,
size_t linkThreshold = 1);
/* Copy SOURCE to DESTINATION, recursively. Throw if SOURCE contains a file
that is not a regular file, symlink, or directory. When DELETESOURCE is
true, delete source files once they have been copied. */
/* Copy SOURCE to DESTINATION, recursively, preserving ownership. Throw if
SOURCE contains a file that is not a regular file, symlink, or directory.
When DELETESOURCE is true, delete source files once they have been
copied. */
void copyFileRecursively(const Path &source, const Path &destination,
bool deleteSource = false);