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Hard-link loop detection for VFS tar file-system

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Detect loops by walking hard-links at two different speeds and checking
for lapping. Tar link walking is no longer a recursive procedure.

Caught a loop created by GNU tar 1.29.

Fix #2611
This commit is contained in:
Emery Hemingway 2017-12-11 21:06:41 -06:00 committed by Christian Helmuth
parent 16b395dce3
commit 4d9037d112
1 changed files with 22 additions and 8 deletions
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30
repos/os/src/lib/vfs/tar_file_system.h
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@ -428,19 +428,33 @@ class Vfs::Tar_file_system : public File_system
/** /**
* Walk hardlinks until we reach a file * Walk hardlinks until we reach a file
*
* XXX: check for hardlink loops
*/ */
Node const *dereference(char const *path) Node const *dereference(char const *path)
{ {
Node const *node = _root_node.lookup(path); Node const *node = _root_node.lookup(path);
if (!node) return 0; Node const *slow_node = node;
int i = 0;
while (node) {
Record const *record = node->record;
if (!record || record->type() != Record::TYPE_HARDLINK)
break; /* got it */
Record const *record = node->record; /*
if (!record || record->type() != Record::TYPE_HARDLINK) * The `node` pointer is followed every iteration and
return node; * `slow_node` every-other iteration. If there is a
* loop then eventually we catch it as the faster
return dereference(record->linked_name()); * laps the slower.
*/
node = _root_node.lookup(record->linked_name());
if (i++ & 1) {
slow_node = _root_node.lookup(slow_node->record->linked_name());
if (node == slow_node) {
Genode::error(_rom_name, " contains a hard-link loop at '", path, "'");
node = nullptr;
}
}
}
return node;
} }
public: public: