Don't read beyond EOF when inserting into sentry page cache.

The sentry page cache stores file contents at page granularity; this is
necessary for memory mappings. Thus file offset ranges passed to
fsutil.FileRangeSet.Fill() must be page-aligned. If the read callback passed to
Fill() returns (partial read, nil error) when reading up to EOF (which is the
case for p9.ClientFile.ReadAt() since 9P's Rread cannot convey both a partial
read and EOF), Fill() will re-invoke the read callback to try to read from EOF
to the end of the containing page, which is harmless but needlessly expensive.
Fix this by handling file size explicitly in fsutil.FileRangeSet.Fill().

PiperOrigin-RevId: 336934075

1 files changed, 6 insertions, 6 deletions

diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index eeaf6e444..f8b19bae7 100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -395,7 +395,7 @@ func (rw *dentryReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error)
 					End:   gapEnd,
 				}
 				optMR := gap.Range()
-				err := rw.d.cache.Fill(rw.ctx, reqMR, maxFillRange(reqMR, optMR), mf, usage.PageCache, h.readToBlocksAt)
+				err := rw.d.cache.Fill(rw.ctx, reqMR, maxFillRange(reqMR, optMR), rw.d.size, mf, usage.PageCache, h.readToBlocksAt)
 				mf.MarkEvictable(rw.d, pgalloc.EvictableRange{optMR.Start, optMR.End})
 				seg, gap = rw.d.cache.Find(rw.off)
 				if !seg.Ok() {
@@ -403,10 +403,10 @@ func (rw *dentryReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error)
 					rw.d.handleMu.RUnlock()
 					return done, err
 				}
-				// err might have occurred in part of gap.Range() outside
-				// gapMR. Forget about it for now; if the error matters and
-				// persists, we'll run into it again in a later iteration of
-				// this loop.
+				// err might have occurred in part of gap.Range() outside gapMR
+				// (in particular, gap.End() might be beyond EOF). Forget about
+				// it for now; if the error matters and persists, we'll run
+				// into it again in a later iteration of this loop.
 			} else {
 				// Read directly from the file.
 				gapDsts := dsts.TakeFirst64(gapMR.Length())
@@ -780,7 +780,7 @@ func (d *dentry) Translate(ctx context.Context, required, optional memmap.Mappab
 
 	mf := d.fs.mfp.MemoryFile()
 	h := d.readHandleLocked()
-	cerr := d.cache.Fill(ctx, required, maxFillRange(required, optional), mf, usage.PageCache, h.readToBlocksAt)
+	cerr := d.cache.Fill(ctx, required, maxFillRange(required, optional), d.size, mf, usage.PageCache, h.readToBlocksAt)
 
 	var ts []memmap.Translation
 	var translatedEnd uint64