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indirect-root-store: Fix race condition in makeSymlink

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Replace rand() with atomic counter and add retry loop to handle
race conditions when creating temporary symlinks for garbage
collector roots.
This commit is contained in:
Jörg Thalheim 2025-06-12 17:40:30 +02:00
parent ef05a2fa0f
commit 975b2c2edd
1 changed files with 26 additions and 5 deletions
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31
src/libstore/indirect-root-store.cc
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@ -1,4 +1,5 @@
#include "nix/store/indirect-root-store.hh"
#include "nix/util/file-system.hh"
namespace nix {
@ -7,12 +8,32 @@ void IndirectRootStore::makeSymlink(const Path & link, const Path & target)
/* Create directories up to `gcRoot'. */
createDirs(dirOf(link));
/* Create the new symlink. */
Path tempLink = fmt("%1%.tmp-%2%-%3%", link, getpid(), rand());
createSymlink(target, tempLink);
/* Retry loop for temporary symlink creation to handle race conditions */
while (true) {
Path tempLink = makeTempPath(dirOf(link), baseNameOf(link) + ".tmp");
/* Atomically replace the old one. */
std::filesystem::rename(tempLink, link);
createSymlink(target, tempLink);
/* Atomically replace the old one. */
try {
std::filesystem::rename(tempLink, link);
break; /* Success! */
} catch (std::filesystem::filesystem_error & e) {
try {
std::filesystem::remove(tempLink);
} catch (...) {
/* Ignore errors removing the temp link */
}
if (e.code() == std::errc::file_exists) {
/* Race condition: another process created the same temp link.
Try again with a different name. */
continue;
}
throw SysError("failed to create symlink '%1%' -> '%2%'", link, target);
}
}
}
Path IndirectRootStore::addPermRoot(const StorePath & storePath, const Path & _gcRoot)