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makeStoreWritable: Use statvfs instead of /proc/self/mountinfo to find out if /nix/store is a read-only bind mount

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/nix/store could be a read-only bind mount even if it is / in its own filesystem, so checking the 4th field in mountinfo is insufficient.

Signed-off-by: Shea Levy <shea@shealevy.com>
This commit is contained in:
Shea Levy 2013-03-07 19:39:55 -05:00 committed by Eelco Dolstra
parent c3fc60d936
commit 2c9cf50746
2 changed files with 14 additions and 22 deletions
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1
configure.ac
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@ -106,6 +106,7 @@ AC_LANG_POP(C++)
# Check for chroot support (requires chroot() and bind mounts).
AC_CHECK_FUNCS([chroot])
AC_CHECK_FUNCS([unshare])
AC_CHECK_FUNCS([statvfs])
AC_CHECK_HEADERS([sched.h])
AC_CHECK_HEADERS([sys/param.h])
AC_CHECK_HEADERS([sys/mount.h], [], [],

25
src/libstore/local-store.cc
View file

@ -19,8 +19,9 @@
#include <stdio.h>
#include <time.h>
#if HAVE_UNSHARE
#if HAVE_UNSHARE && HAVE_STATVFS && HAVE_SYS_MOUNT_H
#include <sched.h>
#include <sys/statvfs.h>
#include <sys/mount.h>
#endif
@ -434,30 +435,20 @@ void LocalStore::openDB(bool create)
bind mount. So make the Nix store writable for this process. */
void LocalStore::makeStoreWritable()
{
#if HAVE_UNSHARE
#if HAVE_UNSHARE && HAVE_STATVFS && HAVE_SYS_MOUNT_H && defined(MS_BIND) && defined(MS_REMOUNT)
if (getuid() != 0) return;
if (!pathExists("/proc/self/mountinfo")) return;
/* Check if /nix/store is a read-only bind mount. */
bool found = false;
Strings mounts = tokenizeString<Strings>(readFile("/proc/self/mountinfo", true), "\n");
foreach (Strings::iterator, i, mounts) {
vector<string> fields = tokenizeString<vector<string> >(*i, " ");
if (fields.at(3) == "/" || fields.at(4) != settings.nixStore) continue;
Strings options = tokenizeString<Strings>(fields.at(5), ",");
if (std::find(options.begin(), options.end(), "ro") == options.end()) continue;
found = true;
break;
}
if (!found) return;
struct statvfs stat;
if (statvfs(settings.nixStore.c_str(), &stat) !=0)
throw SysError("Getting info of nix store mountpoint");
if (stat.f_flag & (ST_RDONLY | MS_BIND)) {
if (unshare(CLONE_NEWNS) == -1)
throw SysError("setting up a private mount namespace");
if (mount(0, settings.nixStore.c_str(), 0, MS_REMOUNT | MS_BIND, 0) == -1)
throw SysError(format("remounting %1% writable") % settings.nixStore);
}
#endif
}