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Merge pull request #2326 from aszlig/fix-symlink-leak

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Fix symlink leak in restricted eval mode
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Eelco Dolstra 2018-08-03 17:01:34 +02:00 committed by GitHub
commit bc65e02d96
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2 changed files with 21 additions and 4 deletions
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14
src/libexpr/eval.cc
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@ -349,19 +349,25 @@ Path EvalState::checkSourcePath(const Path & path_)
bool found = false;
/* First canonicalize the path without symlinks, so we make sure an
* attacker can't append ../../... to a path that would be in allowedPaths
* and thus leak symlink targets.
*/
Path abspath = canonPath(path_);
for (auto & i : *allowedPaths) {
if (isDirOrInDir(path_, i)) {
if (isDirOrInDir(abspath, i)) {
found = true;
break;
}
}
if (!found)
throw RestrictedPathError("access to path '%1%' is forbidden in restricted mode", path_);
throw RestrictedPathError("access to path '%1%' is forbidden in restricted mode", abspath);
/* Resolve symlinks. */
debug(format("checking access to '%s'") % path_);
Path path = canonPath(path_, true);
debug(format("checking access to '%s'") % abspath);
Path path = canonPath(abspath, true);
for (auto & i : *allowedPaths) {
if (isDirOrInDir(path, i)) {

11
tests/restricted.sh
View file

@ -38,3 +38,14 @@ ln -sfn $(pwd)/restricted.nix $TEST_ROOT/restricted.nix
nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix -I $TEST_ROOT -I .
[[ $(nix eval --raw --restrict-eval -I . '(builtins.readFile "${import ./simple.nix}/hello")') == 'Hello World!' ]]
# Check whether we can leak symlink information through directory traversal.
traverseDir="$(pwd)/restricted-traverse-me"
ln -sfn "$(pwd)/restricted-secret" "$(pwd)/restricted-innocent"
mkdir -p "$traverseDir"
goUp="..$(echo "$traverseDir" | sed -e 's,[^/]\+,..,g')"
output="$(nix eval --raw --restrict-eval -I "$traverseDir" \
"(builtins.readFile \"$traverseDir/$goUp$(pwd)/restricted-innocent\")" \
2>&1 || :)"
echo "$output" | grep "is forbidden"
! echo "$output" | grep -F restricted-secret