Move maxListenBacklog check to sentry

Move maxListenBacklog check to the caller of endpoint Listen so that it
is applicable to Unix domain sockets as well.
This was changed in cl/366935921.

Reported-by: syzbot+a35ae7cdfdde0c41cf7a@syzkaller.appspotmail.com
PiperOrigin-RevId: 367728052

1 files changed, 14 insertions, 1 deletions

diff --git a/pkg/sentry/syscalls/linux/vfs2/socket.go b/pkg/sentry/syscalls/linux/vfs2/socket.go
index 7cc0be892..936614eab 100644
--- a/pkg/sentry/syscalls/linux/vfs2/socket.go
+++ b/pkg/sentry/syscalls/linux/vfs2/socket.go
@@ -46,6 +46,9 @@ const maxOptLen = 1024 * 8
 // buffers upto INT_MAX.
 const maxControlLen = 10 * 1024 * 1024
 
+// maxListenBacklog is the maximum limit of listen backlog supported.
+const maxListenBacklog = 1024
+
 // nameLenOffset is the offset from the start of the MessageHeader64 struct to
 // the NameLen field.
 const nameLenOffset = 8
@@ -365,7 +368,7 @@ func Bind(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallC
 // Listen implements the linux syscall listen(2).
 func Listen(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	fd := args[0].Int()
-	backlog := args[1].Int()
+	backlog := args[1].Uint()
 
 	// Get socket from the file descriptor.
 	file := t.GetFileVFS2(fd)
@@ -380,6 +383,16 @@ func Listen(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscal
 		return 0, nil, syserror.ENOTSOCK
 	}
 
+	if backlog > maxListenBacklog {
+		// Linux treats incoming backlog as uint with a limit defined by
+		// sysctl_somaxconn.
+		// https://github.com/torvalds/linux/blob/7acac4b3196/net/socket.c#L1666
+		//
+		// We use the backlog to allocate a channel of that size, hence enforce
+		// a hard limit for the backlog.
+		backlog = maxListenBacklog
+	}
+
 	return 0, nil, s.Listen(t, int(backlog)).ToError()
 }