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syscall: add all ambient capabilities into permitted and inheritable sets

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According to the prctl man page, each capability from the ambient set
must already be present in both  the  permitted  and  the  inheritable
sets  of the process.

exec_linux_test suggests configuring the capabilities in the parent
process. This doesn't look nice, because:
* Capabilities are a per-thread attribute, so we need to use
LockOSThread.
* Need to restore capabilities after creating a process.
* Doesn't work with user namespaces, because a process gets capabilities
when a namespace is created.

Fixes #23152

Change-Id: Iba23e530fc7b9f5182d602fe855f82218f354219
Reviewed-on: https://go-review.googlesource.com/c/go/+/156577
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Andrei Vagin 2019-01-07 10:18:42 -08:00 • committed by Ian Lance Taylor
parent f1d5ce0185
commit 5930c7de93
2 changed files with 87 additions and 20 deletions
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51
src/syscall/exec_linux.go
View file

@ -94,6 +94,29 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
return pid, 0
}
const _LINUX_CAPABILITY_VERSION_3 = 0x20080522
type capHeader struct {
version uint32
pid int32
}
type capData struct {
effective uint32
permitted uint32
inheritable uint32
}
type caps struct {
hdr capHeader
data [2]capData
}
// See CAP_TO_INDEX in linux/capability.h:
func capToIndex(cap uintptr) uintptr { return cap >> 5 }
// See CAP_TO_MASK in linux/capability.h:
func capToMask(cap uintptr) uint32 { return 1 << uint(cap&31) }
// forkAndExecInChild1 implements the body of forkAndExecInChild up to
// the parent's post-fork path. This is a separate function so we can
// separate the child's and parent's stack frames if we're using
@ -122,6 +145,7 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
err2 Errno
nextfd int
i int
caps caps
)
// Record parent PID so child can test if it has died.
@ -286,11 +310,32 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
}
}
for _, c := range sys.AmbientCaps {
_, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0)
if err1 != 0 {
if len(sys.AmbientCaps) != 0 {
// Ambient capabilities were added in the 4.3 kernel,
// so it is safe to always use _LINUX_CAPABILITY_VERSION_3.
caps.hdr.version = _LINUX_CAPABILITY_VERSION_3
if _, _, err1 := RawSyscall(SYS_CAPGET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 {
goto childerror
}
for _, c := range sys.AmbientCaps {
// Add the c capability to the permitted and inheritable capability mask,
// otherwise we will not be able to add it to the ambient capability mask.
caps.data[capToIndex(c)].permitted |= capToMask(c)
caps.data[capToIndex(c)].inheritable |= capToMask(c)
}
if _, _, err1 := RawSyscall(SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 {
goto childerror
}
for _, c := range sys.AmbientCaps {
_, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0)
if err1 != 0 {
goto childerror
}
}
}
// Chdir