From 7c8206bf26b8ef6020b543bbc027305dee8f2308 Mon Sep 17 00:00:00 2001 From: David Kalnischkies Date: Mon, 31 Aug 2015 11:00:12 +0200 Subject: if file is inaccessible for _apt, disable privilege drop in acquire We had a very similar method previously for our own private usage, but with some generalisation we can move this check into the acquire system proper so that all frontends profit from this compatibility change. As we are disabling a security feature here a warning is issued and frontends are advised to consider reworking their download logic if possible. Note that this is implemented as an all or nothing situation: We can't just (not) drop privileges for a subset of the files in a fetcher, so in case you have to download some files with and some without you need to use two fetchers. --- apt-pkg/acquire.cc | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) (limited to 'apt-pkg/acquire.cc') diff --git a/apt-pkg/acquire.cc b/apt-pkg/acquire.cc index f8b077367..cb32e8f2b 100644 --- a/apt-pkg/acquire.cc +++ b/apt-pkg/acquire.cc @@ -34,6 +34,7 @@ #include #include #include +#include #include #include #include @@ -446,8 +447,58 @@ void pkgAcquire::RunFds(fd_set *RSet,fd_set *WSet) /* This runs the queues. It manages a select loop for all of the Worker tasks. The workers interact with the queues and items to manage the actual fetch. */ +static void CheckDropPrivsMustBeDisabled(pkgAcquire const &Fetcher) +{ + if(getuid() != 0) + return; + + std::string SandboxUser = _config->Find("APT::Sandbox::User"); + if (SandboxUser.empty()) + return; + + struct passwd const * const pw = getpwnam(SandboxUser.c_str()); + if (pw == NULL) + return; + + if (setegid(pw->pw_gid) != 0) + _error->Errno("setegid", "setegid %u failed", pw->pw_gid); + if (seteuid(pw->pw_uid) != 0) + _error->Errno("seteuid", "seteuid %u failed", pw->pw_uid); + + bool dropPrivs = true; + for (pkgAcquire::ItemCIterator I = Fetcher.ItemsBegin(); + I != Fetcher.ItemsEnd() && dropPrivs == true; ++I) + { + if ((*I)->DestFile.empty()) + continue; + + // we check directory instead of file as the file might or might not + // exist already as a link or not which complicates everything… + std::string dirname = flNotFile((*I)->DestFile); + if (DirectoryExists(dirname)) + ; + else + continue; // assume it is created correctly by the acquire system + + if (faccessat(AT_FDCWD, dirname.c_str(), R_OK | W_OK | X_OK, AT_EACCESS | AT_SYMLINK_NOFOLLOW) != 0) + { + dropPrivs = false; + _error->WarningE("pkgAcquire::Run", _("Can't drop privileges for downloading as file '%s' couldn't be accessed by user '%s'."), + (*I)->DestFile.c_str(), SandboxUser.c_str()); + _config->Set("APT::Sandbox::User", ""); + break; + } + } + + if (seteuid(0) != 0) + _error->Errno("seteuid", "seteuid %u failed", 0); + if (setegid(0) != 0) + _error->Errno("setegid", "setegid %u failed", 0); +} pkgAcquire::RunResult pkgAcquire::Run(int PulseIntervall) { + CheckDropPrivsMustBeDisabled(*this); + Running = true; for (Queue *I = Queues; I != 0; I = I->Next) -- cgit v1.2.3