pipe: writeLocked has to return ErrWouldBlock if the pipe is full

PiperOrigin-RevId: 356450303

2 files changed, 9 insertions, 2 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
index 6255a7c84..82a743ff3 100644
--- a/pkg/sentry/fsimpl/tmpfs/regular_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -656,6 +656,9 @@ func (rw *regularFileReadWriter) WriteFromBlocks(srcs safemem.BlockSeq) (uint64,
 
 			// Write to that memory as usual.
 			seg, gap = rw.file.data.Insert(gap, gapMR, fr.Start), fsutil.FileRangeGapIterator{}
+
+		default:
+			panic("unreachable")
 		}
 	}
 exitLoop:
diff --git a/pkg/sentry/kernel/pipe/pipe.go b/pkg/sentry/kernel/pipe/pipe.go
index c551acd99..2c8668fc4 100644
--- a/pkg/sentry/kernel/pipe/pipe.go
+++ b/pkg/sentry/kernel/pipe/pipe.go
@@ -247,11 +247,15 @@ func (p *Pipe) writeLocked(count int64, f func(safemem.BlockSeq) (uint64, error)
 		return 0, syscall.EPIPE
 	}
 
-	// POSIX requires that a write smaller than atomicIOBytes (PIPE_BUF) be
-	// atomic, but requires no atomicity for writes larger than this.
 	avail := p.max - p.size
+	if avail == 0 {
+		return 0, syserror.ErrWouldBlock
+	}
 	short := false
 	if count > avail {
+		// POSIX requires that a write smaller than atomicIOBytes
+		// (PIPE_BUF) be atomic, but requires no atomicity for writes
+		// larger than this.
 		if count <= atomicIOBytes {
 			return 0, syserror.ErrWouldBlock
 		}