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Fixes for GHSA-g948-229j-48j3

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Squashed commit of the following:

commit 04fff3a637d455cbb1d75937a235950e43008db9
Author: Eelco Dolstra <edolstra@gmail.com>
Date:   Thu Jun 12 12:30:32 2025 +0200

    Chown structured attr files safely

commit 5417ad445e414c649d0cfc71a05661c7bf8f3ef5
Author: Eelco Dolstra <edolstra@gmail.com>
Date:   Thu Jun 12 12:14:04 2025 +0200

    Replace 'bool sync' with an enum for clarity

    And drop writeFileAndSync().

commit 7ae0141f328d8e8e1094be24665789c05f974ba6
Author: Eelco Dolstra <edolstra@gmail.com>
Date:   Thu Jun 12 11:35:28 2025 +0200

    Drop guessOrInventPathFromFD()

    No need to do hacky stuff like that when we already know the original path.

commit 45b05098bd019da7c57cd4227a89bfd0fa65bb08
Author: Eelco Dolstra <edolstra@gmail.com>
Date:   Thu Jun 12 11:15:58 2025 +0200

    Tweak comment

commit 0af15b31209d1b7ec8addfae9a1a6b60d8f35848
Author: Raito Bezarius <raito@lix.systems>
Date:   Thu Mar 27 12:22:26 2025 +0100

    libstore: ensure that temporary directory is always 0o000 before deletion

    In the case the deletion fails, we should ensure that the temporary
    directory cannot be used for nefarious purposes.

    Change-Id: I498a2dd0999a74195d13642f44a5de1e69d46120
    Signed-off-by: Raito Bezarius <raito@lix.systems>

commit 2c20fa37b15cfa03ac6a1a6a47cdb2ed66c0827e
Author: Raito Bezarius <raito@lix.systems>
Date:   Wed Mar 26 12:42:55 2025 +0100

    libutil: ensure that `_deletePath` does NOT use absolute paths with dirfds

    When calling `_deletePath` with a parent file descriptor, `openat` is
    made effective by using relative paths to the directory file descriptor.

    To avoid the problem, the signature is changed to resist misuse with an
    assert in the prologue of the function.

    Change-Id: I6b3fc766bad2afe54dc27d47d1df3873e188de96
    Signed-off-by: Raito Bezarius <raito@lix.systems>

commit d3c370bbcae48bb825ce19fd0f73bb4eefd2c9ea
Author: Raito Bezarius <raito@lix.systems>
Date:   Wed Mar 26 01:07:47 2025 +0100

    libstore: ensure that `passAsFile` is created in the original temp dir

    This ensures that `passAsFile` data is created inside the expected
    temporary build directory by `openat()` from the parent directory file
    descriptor.

    This avoids a TOCTOU which is part of the attack chain of CVE-????.

    Change-Id: Ie5273446c4a19403088d0389ae8e3f473af8879a
    Signed-off-by: Raito Bezarius <raito@lix.systems>

commit 45d3598724f932d024ef6bc2ffb00c1bb90e6018
Author: Raito Bezarius <raito@lix.systems>
Date:   Wed Mar 26 01:06:03 2025 +0100

    libutil: writeFile variant for file descriptors

    `writeFile` lose its `sync` boolean flag to make things simpler.

    A new `writeFileAndSync` function is created and all call sites are
    converted to it.

    Change-Id: Ib871a5283a9c047db1e4fe48a241506e4aab9192
    Signed-off-by: Raito Bezarius <raito@lix.systems>

commit 732bd9b98cabf4aaf95a01fd318923de303f9996
Author: Raito Bezarius <raito@lix.systems>
Date:   Wed Mar 26 01:05:34 2025 +0100

    libstore: chown to builder variant for file descriptors

    We use it immediately for the build temporary directory.

    Change-Id: I180193c63a2b98721f5fb8e542c4e39c099bb947
    Signed-off-by: Raito Bezarius <raito@lix.systems>

commit 962c65f8dcd5570dd92c72370a862c7b38942e0d
Author: Raito Bezarius <raito@lix.systems>
Date:   Wed Mar 26 01:04:59 2025 +0100

    libstore: open build directory as a dirfd as well

    We now keep around a proper AutoCloseFD around the temporary directory
    which we plan to use for openat operations and avoiding the build
    directory being swapped out while we are doing something else.

    Change-Id: I18d387b0f123ebf2d20c6405cd47ebadc5505f2a
    Signed-off-by: Raito Bezarius <raito@lix.systems>

commit c9b42462b75b5a37ee6564c2b53cff186c8323da
Author: Raito Bezarius <raito@lix.systems>
Date:   Wed Mar 26 01:04:12 2025 +0100

    libutil: guess or invent a path from file descriptors

    This is useful for certain error recovery paths (no pun intended) that
    does not thread through the original path name.

    Change-Id: I2d800740cb4f9912e64c923120d3f977c58ccb7e
    Signed-off-by: Raito Bezarius <raito@lix.systems>
This commit is contained in:
Eelco Dolstra 2025-06-19 16:20:34 +02:00
parent 7d15dbf9d5
commit b0fab9f90b
5 changed files with 97 additions and 36 deletions
Download patch file Download diff file Expand all files Collapse all files

6
src/libstore/local-store.cc
View file

@ -187,7 +187,7 @@ void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
txn.commit();
}
writeFile(schemaPath, fmt("%d", nixCASchemaVersion), 0666, true);
writeFile(schemaPath, fmt("%d", nixCASchemaVersion), 0666, FsSync::Yes);
lockFile(lockFd.get(), ltRead, true);
}
}
@ -345,7 +345,7 @@ LocalStore::LocalStore(
else if (curSchema == 0) { /* new store */
curSchema = nixSchemaVersion;
openDB(*state, true);
writeFile(schemaPath, fmt("%1%", curSchema), 0666, true);
writeFile(schemaPath, fmt("%1%", curSchema), 0666, FsSync::Yes);
}
else if (curSchema < nixSchemaVersion) {
@ -394,7 +394,7 @@ LocalStore::LocalStore(
txn.commit();
}
writeFile(schemaPath, fmt("%1%", nixSchemaVersion), 0666, true);
writeFile(schemaPath, fmt("%1%", nixSchemaVersion), 0666, FsSync::Yes);
lockFile(globalLock.get(), ltRead, true);
}

46
src/libstore/unix/build/local-derivation-goal.cc
View file

@ -526,7 +526,14 @@ void LocalDerivationGoal::startBuilder()
} else {
tmpDir = topTmpDir;
}
chownToBuilder(tmpDir);
/* The TOCTOU between the previous mkdir call and this open call is unavoidable due to
POSIX semantics.*/
tmpDirFd = AutoCloseFD{open(tmpDir.c_str(), O_RDONLY | O_NOFOLLOW | O_DIRECTORY)};
if (!tmpDirFd)
throw SysError("failed to open the build temporary directory descriptor '%1%'", tmpDir);
chownToBuilder(tmpDirFd.get(), tmpDir);
for (auto & [outputName, status] : initialOutputs) {
/* Set scratch path we'll actually use during the build.
@ -1110,9 +1117,7 @@ void LocalDerivationGoal::initTmpDir() {
} else {
auto hash = hashString(HashAlgorithm::SHA256, i.first);
std::string fn = ".attr-" + hash.to_string(HashFormat::Nix32, false);
Path p = tmpDir + "/" + fn;
writeFile(p, rewriteStrings(i.second, inputRewrites));
chownToBuilder(p);
writeBuilderFile(fn, rewriteStrings(i.second, inputRewrites));
env[i.first + "Path"] = tmpDirInSandbox + "/" + fn;
}
}
@ -1217,11 +1222,9 @@ void LocalDerivationGoal::writeStructuredAttrs()
auto jsonSh = writeStructuredAttrsShell(json);
writeFile(tmpDir + "/.attrs.sh", rewriteStrings(jsonSh, inputRewrites));
chownToBuilder(tmpDir + "/.attrs.sh");
writeBuilderFile(".attrs.sh", rewriteStrings(jsonSh, inputRewrites));
env["NIX_ATTRS_SH_FILE"] = tmpDirInSandbox + "/.attrs.sh";
writeFile(tmpDir + "/.attrs.json", rewriteStrings(json.dump(), inputRewrites));
chownToBuilder(tmpDir + "/.attrs.json");
writeBuilderFile(".attrs.json", rewriteStrings(json.dump(), inputRewrites));
env["NIX_ATTRS_JSON_FILE"] = tmpDirInSandbox + "/.attrs.json";
}
}
@ -1730,6 +1733,24 @@ void setupSeccomp()
#endif
}
void LocalDerivationGoal::chownToBuilder(int fd, const Path & path)
{
if (!buildUser) return;
if (fchown(fd, buildUser->getUID(), buildUser->getGID()) == -1)
throw SysError("cannot change ownership of file '%1%'", path);
}
void LocalDerivationGoal::writeBuilderFile(
const std::string & name,
std::string_view contents)
{
auto path = std::filesystem::path(tmpDir) / name;
AutoCloseFD fd{openat(tmpDirFd.get(), name.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC | O_EXCL | O_NOFOLLOW, 0666)};
if (!fd)
throw SysError("creating file %s", path);
writeFile(fd, path, contents);
chownToBuilder(fd.get(), path);
}
void LocalDerivationGoal::runChild()
{
@ -3006,6 +3027,15 @@ void LocalDerivationGoal::checkOutputs(const std::map<std::string, ValidPathInfo
void LocalDerivationGoal::deleteTmpDir(bool force)
{
if (topTmpDir != "") {
/* As an extra precaution, even in the event of `deletePath` failing to
* clean up, the `tmpDir` will be chowned as if we were to move
* it inside the Nix store.
*
* This hardens against an attack which smuggles a file descriptor
* to make use of the temporary directory.
*/
chmod(topTmpDir.c_str(), 0000);
/* Don't keep temporary directories for builtins because they
might have privileged stuff (like a copy of netrc). */
if (settings.keepFailed && !force && !drv->isBuiltin()) {

20
src/libstore/unix/build/local-derivation-goal.hh
View file

@ -37,6 +37,11 @@ struct LocalDerivationGoal : public DerivationGoal
*/
Path topTmpDir;
/**
* The file descriptor of the temporary directory.
*/
AutoCloseFD tmpDirFd;
/**
* The path of the temporary directory in the sandbox.
*/
@ -232,9 +237,24 @@ struct LocalDerivationGoal : public DerivationGoal
/**
* Make a file owned by the builder.
*
* SAFETY: this function is prone to TOCTOU as it receives a path and not a descriptor.
* It's only safe to call in a child of a directory only visible to the owner.
*/
void chownToBuilder(const Path & path);
/**
* Make a file owned by the builder addressed by its file descriptor.
*/
void chownToBuilder(int fd, const Path & path);
/**
* Create a file in `tmpDir` owned by the builder.
*/
void writeBuilderFile(
const std::string & name,
std::string_view contents);
int getChildStatus() override;
/**

53
src/libutil/file-system.cc
View file

@ -247,7 +247,7 @@ void readFile(const Path & path, Sink & sink)
}
void writeFile(const Path & path, std::string_view s, mode_t mode, bool sync)
void writeFile(const Path & path, std::string_view s, mode_t mode, FsSync sync)
{
AutoCloseFD fd = toDescriptor(open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT
// TODO
@ -257,22 +257,29 @@ void writeFile(const Path & path, std::string_view s, mode_t mode, bool sync)
, mode));
if (!fd)
throw SysError("opening file '%1%'", path);
try {
writeFull(fd.get(), s);
} catch (Error & e) {
e.addTrace({}, "writing file '%1%'", path);
throw;
}
if (sync)
fd.fsync();
// Explicitly close to make sure exceptions are propagated.
writeFile(fd, path, s, mode, sync);
/* Close explicitly to propagate the exceptions. */
fd.close();
if (sync)
syncParent(path);
}
void writeFile(AutoCloseFD & fd, const Path & origPath, std::string_view s, mode_t mode, FsSync sync)
{
assert(fd);
try {
writeFull(fd.get(), s);
void writeFile(const Path & path, Source & source, mode_t mode, bool sync)
if (sync == FsSync::Yes)
fd.fsync();
} catch (Error & e) {
e.addTrace({}, "writing file '%1%'", origPath);
throw;
}
}
void writeFile(const Path & path, Source & source, mode_t mode, FsSync sync)
{
AutoCloseFD fd = toDescriptor(open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT
// TODO
@ -296,11 +303,11 @@ void writeFile(const Path & path, Source & source, mode_t mode, bool sync)
e.addTrace({}, "writing file '%1%'", path);
throw;
}
if (sync)
if (sync == FsSync::Yes)
fd.fsync();
// Explicitly close to make sure exceptions are propagated.
fd.close();
if (sync)
if (sync == FsSync::Yes)
syncParent(path);
}
@ -318,7 +325,8 @@ static void _deletePath(Descriptor parentfd, const fs::path & path, uint64_t & b
#ifndef _WIN32
checkInterrupt();
std::string name(baseNameOf(path.native()));
std::string name(path.filename());
assert(name != "." && name != ".." && !name.empty());
struct stat st;
if (fstatat(parentfd, name.c_str(), &st,
@ -359,7 +367,7 @@ static void _deletePath(Descriptor parentfd, const fs::path & path, uint64_t & b
throw SysError("chmod '%1%'", path);
}
int fd = openat(parentfd, path.c_str(), O_RDONLY);
int fd = openat(parentfd, name.c_str(), O_RDONLY | O_DIRECTORY | O_NOFOLLOW);
if (fd == -1)
throw SysError("opening directory '%1%'", path);
AutoCloseDir dir(fdopendir(fd));
@ -371,7 +379,7 @@ static void _deletePath(Descriptor parentfd, const fs::path & path, uint64_t & b
checkInterrupt();
std::string childName = dirent->d_name;
if (childName == "." || childName == "..") continue;
_deletePath(dirfd(dir.get()), path + "/" + childName, bytesFreed);
_deletePath(dirfd(dir.get()), path / childName, bytesFreed);
}
if (errno) throw SysError("reading directory '%1%'", path);
}
@ -389,14 +397,13 @@ static void _deletePath(Descriptor parentfd, const fs::path & path, uint64_t & b
static void _deletePath(const fs::path & path, uint64_t & bytesFreed)
{
Path dir = dirOf(path.string());
if (dir == "")
dir = "/";
assert(path.is_absolute());
assert(path.parent_path() != path);
AutoCloseFD dirfd = toDescriptor(open(dir.c_str(), O_RDONLY));
AutoCloseFD dirfd = toDescriptor(open(path.parent_path().string().c_str(), O_RDONLY));
if (!dirfd) {
if (errno == ENOENT) return;
throw SysError("opening directory '%1%'", path);
throw SysError("opening directory %s", path.parent_path());
}
_deletePath(dirfd.get(), path, bytesFreed);

8
src/libutil/file-system.hh
View file

@ -148,12 +148,16 @@ Descriptor openDirectory(const std::filesystem::path & path);
std::string readFile(const Path & path);
void readFile(const Path & path, Sink & sink);
enum struct FsSync { Yes, No };
/**
* Write a string to a file.
*/
void writeFile(const Path & path, std::string_view s, mode_t mode = 0666, bool sync = false);
void writeFile(const Path & path, std::string_view s, mode_t mode = 0666, FsSync sync = FsSync::No);
void writeFile(const Path & path, Source & source, mode_t mode = 0666, bool sync = false);
void writeFile(const Path & path, Source & source, mode_t mode = 0666, FsSync sync = FsSync::No);
void writeFile(AutoCloseFD & fd, const Path & origPath, std::string_view s, mode_t mode = 0666, FsSync sync = FsSync::No);
/**
* Flush a file's parent directory to disk