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authorEelco Dolstra <edolstra@gmail.com>2017-07-04T13·43+0200
committerEelco Dolstra <edolstra@gmail.com>2017-07-04T13·48+0200
commit6cf23c3e8fa12e6bf297ca87d1b47889bf115d52 (patch)
treeee3a793b215fc0d1cca59034a61171b19c1aa77b /src
parentad8b96f1f2c80bf3f91ceab4d955aa368b7c85d4 (diff)
Add allow-new-privileges option
This allows builds to call setuid binaries. This was previously
possible until we started using seccomp. Turns out that seccomp by
default disallows processes from acquiring new privileges. Generally,
any use of setuid binaries (except those created by the builder
itself) is by definition impure, but some people were relying on this
ability for certain tests.

Example:

  $ nix build '(with import <nixpkgs> {}; runCommand "foo" {} "/run/wrappers/bin/ping -c 1 8.8.8.8; exit 1")' --no-allow-new-privileges
  builder for ‘/nix/store/j0nd8kv85hd6r4kxgnwzvr0k65ykf6fv-foo.drv’ failed with exit code 1; last 2 log lines:
    cannot raise the capability into the Ambient set
    : Operation not permitted

  $ nix build '(with import <nixpkgs> {}; runCommand "foo" {} "/run/wrappers/bin/ping -c 1 8.8.8.8; exit 1")' --allow-new-privileges
  builder for ‘/nix/store/j0nd8kv85hd6r4kxgnwzvr0k65ykf6fv-foo.drv’ failed with exit code 1; last 6 log lines:
    PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
    64 bytes from 8.8.8.8: icmp_seq=1 ttl=46 time=15.2 ms

Fixes #1429.
Diffstat (limited to 'src')
-rw-r--r--src/libstore/build.cc3
-rw-r--r--src/libstore/globals.hh6
2 files changed, 9 insertions, 0 deletions
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index f40a8c5498ee..355fb3b7dfe5 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2340,6 +2340,9 @@ void setupSeccomp()
         seccomp_rule_add(ctx, SCMP_ACT_ERRNO(ENOTSUP), SCMP_SYS(fsetxattr), 0) != 0)
         throw SysError("unable to add seccomp rule");
 
+    if (seccomp_attr_set(ctx, SCMP_FLTATR_CTL_NNP, settings.allowNewPrivileges ? 0 : 1) != 0)
+        throw SysError("unable to set 'no new privileges' seccomp attribute");
+
     if (seccomp_load(ctx) != 0)
         throw SysError("unable to load seccomp BPF program");
 #endif
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index af37ec61d7a1..c8d67b07110b 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -321,6 +321,12 @@ public:
 
     Setting<std::string> userAgentSuffix{this, "", "user-agent-suffix",
         "String appended to the user agent in HTTP requests."};
+
+#if __linux__
+    Setting<bool> allowNewPrivileges{this, false, "allow-new-privileges",
+        "Whether builders can acquire new privileges by calling programs with "
+        "setuid/setgid bits or with file capabilities."};
+#endif
 };