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libexpr: Fix prim_replaceStrings() to work on an empty source string

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Otherwise, running e.g.

nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'

would just hang in an infinite loop.

Found by afl-fuzz.

First attempt of this was reverted in e2d71bd186 because it caused
another infinite loop, which is fixed now and a test added.
This commit is contained in:
Tuomas Tynkkynen 2018-02-19 17:52:33 +02:00
parent 24ec750003
commit 77e9e1ed91
3 changed files with 18 additions and 4 deletions
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17
src/libexpr/primops.cc
View file

@ -1913,21 +1913,32 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
auto s = state.forceString(*args[2], context, pos); auto s = state.forceString(*args[2], context, pos);
string res; string res;
for (size_t p = 0; p < s.size(); ) { // Loops one past last character to handle the case where 'from' contains an empty string.
for (size_t p = 0; p <= s.size(); ) {
bool found = false; bool found = false;
auto i = from.begin(); auto i = from.begin();
auto j = to.begin(); auto j = to.begin();
for (; i != from.end(); ++i, ++j) for (; i != from.end(); ++i, ++j)
if (s.compare(p, i->size(), *i) == 0) { if (s.compare(p, i->size(), *i) == 0) {
found = true; found = true;
p += i->size();
res += j->first; res += j->first;
if (i->empty()) {
if (p < s.size())
res += s[p];
p++;
} else {
p += i->size();
}
for (auto& path : j->second) for (auto& path : j->second)
context.insert(path); context.insert(path);
j->second.clear(); j->second.clear();
break; break;
} }
if (!found) res += s[p++]; if (!found) {
if (p < s.size())
res += s[p];
p++;
}
} }
mkString(v, res, context); mkString(v, res, context);

2
tests/lang/eval-okay-replacestrings.exp
View file

@ -1 +1 @@
[ "faabar" "fbar" "fubar" "faboor" "fubar" ] [ "faabar" "fbar" "fubar" "faboor" "fubar" "XaXbXcX" "X" "a_b" ]

3
tests/lang/eval-okay-replacestrings.nix
View file

@ -5,4 +5,7 @@ with builtins;
(replaceStrings ["oo"] ["u"] "foobar") (replaceStrings ["oo"] ["u"] "foobar")
(replaceStrings ["oo" "a"] ["a" "oo"] "foobar") (replaceStrings ["oo" "a"] ["a" "oo"] "foobar")
(replaceStrings ["oo" "oo"] ["u" "i"] "foobar") (replaceStrings ["oo" "oo"] ["u" "i"] "foobar")
(replaceStrings [""] ["X"] "abc")
(replaceStrings [""] ["X"] "")
(replaceStrings ["-"] ["_"] "a-b")
] ]