Create stubs for syscalls upto Linux 4.4.

Create syscall stubs for missing syscalls upto Linux 4.4 and advertise
a kernel version of 4.4.

PiperOrigin-RevId: 220667680
Change-Id: Idbdccde538faabf16debc22f492dd053a8af0ba7

4 files changed, 3 insertions, 11 deletions

diff --git a/pkg/sentry/fs/inode.go b/pkg/sentry/fs/inode.go
index 95769ccf8..38b140bd2 100644
--- a/pkg/sentry/fs/inode.go
+++ b/pkg/sentry/fs/inode.go
@@ -439,10 +439,7 @@ func (i *Inode) CheckOwnership(ctx context.Context) bool {
 // CheckCapability checks whether `ctx` has capability `cp` with respect to
 // operations on this Inode.
 //
-// Compare Linux's kernel/capability.c:capable_wrt_inode_uidgid(). Note that
-// this function didn't exist in Linux 3.11.10, but was added by upstream
-// 23adbe12ef7d "fs,userns: Change inode_capable to capable_wrt_inode_uidgid"
-// to fix local privilege escalation CVE-2014-4014.
+// Compare Linux's kernel/capability.c:capable_wrt_inode_uidgid().
 func (i *Inode) CheckCapability(ctx context.Context, cp linux.Capability) bool {
 	uattr, err := i.UnstableAttr(ctx)
 	if err != nil {
diff --git a/pkg/sentry/fs/proc/README.md b/pkg/sentry/fs/proc/README.md
index e1ed88512..686d40f0c 100644
--- a/pkg/sentry/fs/proc/README.md
+++ b/pkg/sentry/fs/proc/README.md
@@ -223,7 +223,7 @@ Number of seconds idle           | Always zero
 
 ```bash
 $ cat /proc/version
-Linux version 3.11.10 #1 SMP Fri Nov 29 10:47:50 PST 2013
+Linux version 4.4 #1 SMP Sun Jan 10 15:06:54 PST 2016
 ```
 
 ## Process-specific data
diff --git a/pkg/sentry/fs/proc/fds.go b/pkg/sentry/fs/proc/fds.go
index 5ebb33703..5acbce75e 100644
--- a/pkg/sentry/fs/proc/fds.go
+++ b/pkg/sentry/fs/proc/fds.go
@@ -173,11 +173,6 @@ func (f *fdDir) Check(ctx context.Context, inode *fs.Inode, req fs.PermMask) boo
 	if t := kernel.TaskFromContext(ctx); t != nil {
 		// Allow access if the task trying to access it is in the
 		// thread group corresponding to this directory.
-		//
-		// N.B. Technically, in Linux 3.11, this compares what would be
-		// the equivalent of task pointers. However, this was fixed
-		// later in 54708d2858e7 ("proc: actually make
-		// proc_fd_permission() thread-friendly").
 		if f.t.ThreadGroup() == t.ThreadGroup() {
 			return true
 		}
diff --git a/pkg/sentry/fs/proc/task.go b/pkg/sentry/fs/proc/task.go
index 404faea0a..9f13ff91c 100644
--- a/pkg/sentry/fs/proc/task.go
+++ b/pkg/sentry/fs/proc/task.go
@@ -76,7 +76,7 @@ func newTaskDir(t *kernel.Task, msrc *fs.MountSource, pidns *kernel.PIDNamespace
 		"gid_map": newGIDMap(t, msrc),
 		// TODO: This is incorrect for /proc/[pid]/task/[tid]/io, i.e. if
 		// showSubtasks is false:
-		// http://lxr.free-electrons.com/source/fs/proc/base.c?v=3.11#L2980
+		// https://elixir.bootlin.com/linux/v4.4/source/fs/proc/base.c#L3154
 		"io":        newIO(t, msrc),
 		"maps":      newMaps(t, msrc),
 		"mountinfo": seqfile.NewSeqFileInode(t, &mountInfoFile{t: t}, msrc),