Fix VFS2 getdents()/getdents64() alignment.

PiperOrigin-RevId: 306263615

1 files changed, 16 insertions, 4 deletions

diff --git a/pkg/sentry/syscalls/linux/vfs2/getdents.go b/pkg/sentry/syscalls/linux/vfs2/getdents.go
index a61cc5059..62e98817d 100644
--- a/pkg/sentry/syscalls/linux/vfs2/getdents.go
+++ b/pkg/sentry/syscalls/linux/vfs2/getdents.go
@@ -97,6 +97,7 @@ func (cb *getdentsCallback) Handle(dirent vfs.Dirent) error {
 		//     char           d_name[]; /* Filename (null-terminated) */
 		// };
 		size := 8 + 8 + 2 + 1 + 1 + len(dirent.Name)
+		size = (size + 7) &^ 7 // round up to multiple of 8
 		if size > cb.remaining {
 			return syserror.EINVAL
 		}
@@ -106,7 +107,12 @@ func (cb *getdentsCallback) Handle(dirent vfs.Dirent) error {
 		usermem.ByteOrder.PutUint16(buf[16:18], uint16(size))
 		buf[18] = dirent.Type
 		copy(buf[19:], dirent.Name)
-		buf[size-1] = 0 // NUL terminator
+		// Zero out all remaining bytes in buf, including the NUL terminator
+		// after dirent.Name.
+		bufTail := buf[19+len(dirent.Name):]
+		for i := range bufTail {
+			bufTail[i] = 0
+		}
 	} else {
 		// struct linux_dirent {
 		//     unsigned long  d_ino;     /* Inode number */
@@ -125,6 +131,7 @@ func (cb *getdentsCallback) Handle(dirent vfs.Dirent) error {
 			panic(fmt.Sprintf("unsupported sizeof(unsigned long): %d", cb.t.Arch().Width()))
 		}
 		size := 8 + 8 + 2 + 1 + 1 + 1 + len(dirent.Name)
+		size = (size + 7) &^ 7 // round up to multiple of sizeof(long)
 		if size > cb.remaining {
 			return syserror.EINVAL
 		}
@@ -133,9 +140,14 @@ func (cb *getdentsCallback) Handle(dirent vfs.Dirent) error {
 		usermem.ByteOrder.PutUint64(buf[8:16], uint64(dirent.NextOff))
 		usermem.ByteOrder.PutUint16(buf[16:18], uint16(size))
 		copy(buf[18:], dirent.Name)
-		buf[size-3] = 0 // NUL terminator
-		buf[size-2] = 0 // zero padding byte
-		buf[size-1] = dirent.Type
+		// Zero out all remaining bytes in buf, including the NUL terminator
+		// after dirent.Name and the zero padding byte between the name and
+		// dirent type.
+		bufTail := buf[18+len(dirent.Name):]
+		for i := range bufTail {
+			bufTail[i] = 0
+		}
+		bufTail[2] = dirent.Type
 	}
 	n, err := cb.t.CopyOutBytes(cb.addr, buf)
 	if err != nil {