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lix/tests/restricted.sh
aszlig 43e28a1b75
Fix symlink leak in restricted eval mode
In EvalState::checkSourcePath, the path is checked against the list of
allowed paths first and later it's checked again *after* resolving
symlinks.

The resolving of the symlinks is done via canonPath, which also strips
out "../" and "./". However after the canonicalisation the error message
pointing out that the path is not allowed prints the symlink target in
the error message.

Even if we'd suppress the message, symlink targets could still be leaked
if the symlink target doesn't exist (in this case the error is thrown in
canonPath).

So instead, we now do canonPath() without symlink resolving first before
even checking against the list of allowed paths and then later do the
symlink resolving and checking the allowed paths again.

The first call to canonPath() should get rid of all the "../" and "./",
so in theory the only way to leak a symlink if the attacker is able to
put a symlink in one of the paths allowed by restricted evaluation mode.

For the latter I don't think this is part of the threat model, because
if the attacker can write to that path, the attack vector is even
larger.

Signed-off-by: aszlig <aszlig@nix.build>
2018-08-03 06:46:43 +02:00

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source common.sh
clearStore
nix-instantiate --restrict-eval --eval -E '1 + 2'
(! nix-instantiate --restrict-eval ./restricted.nix)
(! nix-instantiate --eval --restrict-eval <(echo '1 + 2'))
nix-instantiate --restrict-eval ./simple.nix -I src=.
nix-instantiate --restrict-eval ./simple.nix -I src1=simple.nix -I src2=config.nix -I src3=./simple.builder.sh
(! nix-instantiate --restrict-eval --eval -E 'builtins.readFile ./simple.nix')
nix-instantiate --restrict-eval --eval -E 'builtins.readFile ./simple.nix' -I src=..
(! nix-instantiate --restrict-eval --eval -E 'builtins.readDir ../src/nix-channel')
nix-instantiate --restrict-eval --eval -E 'builtins.readDir ../src/nix-channel' -I src=../src
(! nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>')
nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>' -I src=.
p=$(nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --restrict-eval --allowed-uris "file://$(pwd)")
cmp $p restricted.sh
(! nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --restrict-eval)
(! nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --restrict-eval --allowed-uris "file://$(pwd)/restricted.sh/")
nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --restrict-eval --allowed-uris "file://$(pwd)/restricted.sh"
(! nix eval --raw "(builtins.fetchurl https://github.com/NixOS/patchelf/archive/master.tar.gz)" --restrict-eval)
(! nix eval --raw "(builtins.fetchTarball https://github.com/NixOS/patchelf/archive/master.tar.gz)" --restrict-eval)
(! nix eval --raw "(fetchGit git://github.com/NixOS/patchelf.git)" --restrict-eval)
ln -sfn $(pwd)/restricted.nix $TEST_ROOT/restricted.nix
[[ $(nix-instantiate --eval $TEST_ROOT/restricted.nix) == 3 ]]
(! nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix)
(! nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix -I $TEST_ROOT)
(! nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix -I .)
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