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bugfix: Adding depth limit to resolveExprPath

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There is no termination condition for evaluation of cyclical
expression paths which can lead to infinite loops. This addresses
one spot in the parser in a similar fashion as utils.cc/canonPath
does.

This issue can be reproduced by something like:

```
ln -s a b
ln -s b a

nix-instantiate -E 'import ./a'
```
This commit is contained in:
Dima 2019-12-13 14:44:14 +01:00
parent 3e787423c2
commit d89d9958a7
1 changed files with 5 additions and 0 deletions
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5
src/libexpr/parser.y
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@ -576,10 +576,15 @@ Path resolveExprPath(Path path)
{
assert(path[0] == '/');
unsigned int followCount = 0, maxFollow = 1024;
/* If `path' is a symlink, follow it. This is so that relative
path references work. */
struct stat st;
while (true) {
// Basic cycle/depth limit to avoid infinite loops.
if (++followCount >= maxFollow)
throw Error(format("can't resolve expression. infinite symlink recursion in path '%1%'") % path);
if (lstat(path.c_str(), &st))
throw SysError(format("getting status of '%1%'") % path);
if (!S_ISLNK(st.st_mode)) break;