This clarifies comments about static linking made in commit a8608b5b67.
1. There are two ways to create a static binary, one is to disable
cgo, the other is to set linker flags. When cgo is disabled,
there is no need to use osusergo build tag.
2. osusergo only needs to be set when linking against glibc.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
TL;DR: there is no way to do this right.
We do know that in some combination of build tags set (or unset),
linker flags, environment variables, and libc implementation,
this package won't work right. In fact, there is one specific
combination:
1. `CGO_ENABLED=1` (or unset)
2. static binary is being built (e.g. `go build` is run with `-extldflags -static`)
3. `go build` links the binary against glibc
4. `osusergo` is not set
This particular combination results in the following legitimate linker warning:
> cgo_lookup_unix.go: warning: Using 'getpwuid_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
If this warning is ignored and the resulting binary is used on a system
with files from a different glibc version (or without those files), it
could result in a segfault.
The commit being reverted tried to guard against such possibility,
but the problem is, we can only use build tags to account for items
1 and 4 from the above list, while items 2 and 3 do not result in
any build tags being set or unset, making this guard excessive.
Remove it.
This reverts commit 023b072288.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
This is to ensure that users of the homedir package cannot
compile statically (CGO_ENABLED=0) without also setting the osusergo
build tag.
Signed-off-by: Tibor Vass <tibor@docker.com>
About github.com/opencontainers/runc/libcontainer/user:
According to 195d8d544a
this package has two functions:
- Have a static implementation of user lookup, which is now supported in the
os/user stdlib package with the osusergo build tag, but wasn't at the time.
- Have extra functions that os/user doesn't have, but none of those are used
in homedir.
Since https://github.com/moby/moby/pull/11287, homedir depended directly on
libcontainer's user package for CurrentUser().
This is being replaced with os/user.Current(), because all of our static
binaries are compiled with the osusergo tag, and for dynamic libraries it
is more correct to use libc's implementation than parsing /etc/passwd.
About github.com/docker/docker/pkg/idtools:
Only dependency was from GetStatic() which uses idtools.LookupUID(uid).
The implementation of idtools.LookupUID just calls to
github.com/opencontainers/runc/libcontainer/user.LookupUid or fallbacks
to exec-ing to getent (since https://github.com/moby/moby/pull/27599).
This patch replaces calls to homedir.GetStatic by homedir.Get(), opting out
of supporting nss lookups in static binaries via exec-ing to getent for
the homedir package.
If homedir package users need to support nss lookups, they are advised
to compile dynamically instead.
Signed-off-by: Tibor Vass <tibor@docker.com>
libcontainer/user does not build at all on Windows any more, and
this was breaking the client on Windows with upstream `runc`. As
these functions are not used anyway, just split out and stop
checking `runtime`.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
