Linux: Rewrite __old_getdents64 [BZ #23497]

Commit 298d0e3129c0b5137f4989275b13fe30d0733c4d ("Consolidate Linux
getdents{64} implementation") broke the implementation because it does
not take into account struct offset differences.

The new implementation is close to the old one, before the
consolidation, but has been cleaned up slightly.

1 files changed, 64 insertions, 25 deletions

diff --git a/sysdeps/unix/sysv/linux/getdents64.c b/sysdeps/unix/sysv/linux/getdents64.c
index 3bde0cf4f0..bc140b5a7f 100644
--- a/sysdeps/unix/sysv/linux/getdents64.c
+++ b/sysdeps/unix/sysv/linux/getdents64.c
@@ -33,41 +33,80 @@ strong_alias (__getdents64, __getdents)
 # include <shlib-compat.h>
 
 # if SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2)
-# include <olddirent.h>
+#  include <olddirent.h>
+#  include <unistd.h>
 
-/* kernel definition of as of 3.2.  */
-struct compat_linux_dirent
+static ssize_t
+handle_overflow (int fd, __off64_t offset, ssize_t count)
 {
-  /* Both d_ino and d_off are compat_ulong_t which are defined in all
-     architectures as 'u32'.  */
-  uint32_t        d_ino;
-  uint32_t        d_off;
-  unsigned short  d_reclen;
-  char            d_name[1];
-};
+  /* If this is the first entry in the buffer, we can report the
+     error.  */
+  if (count == 0)
+    {
+      __set_errno (EOVERFLOW);
+      return -1;
+    }
+
+  /* Otherwise, seek to the overflowing entry, so that the next call
+     will report the error, and return the data read so far..  */
+  if (__lseek64 (fd, offset, SEEK_SET) != 0)
+    return -1;
+  return count;
+}
 
 ssize_t
 __old_getdents64 (int fd, char *buf, size_t nbytes)
 {
-  ssize_t retval = INLINE_SYSCALL_CALL (getdents, fd, buf, nbytes);
+  /* We do not move the individual directory entries.  This is only
+     possible if the target type (struct __old_dirent64) is smaller
+     than the source type.  */
+  _Static_assert (offsetof (struct __old_dirent64, d_name)
+		  <= offsetof (struct dirent64, d_name),
+		  "__old_dirent64 is larger than dirent64");
+  _Static_assert (__alignof__ (struct __old_dirent64)
+		  <= __alignof__ (struct dirent64),
+		  "alignment of __old_dirent64 is larger than dirent64");
 
-  /* The kernel added the d_type value after the name.  Change this now.  */
-  if (retval != -1)
+  ssize_t retval = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
+  if (retval > 0)
     {
-      union
-      {
-	struct compat_linux_dirent k;
-	struct dirent u;
-      } *kbuf = (void *) buf;
-
-      while ((char *) kbuf < buf + retval)
+      char *p = buf;
+      char *end = buf + retval;
+      while (p < end)
 	{
-	  char d_type = *((char *) kbuf + kbuf->k.d_reclen - 1);
-	  memmove (kbuf->u.d_name, kbuf->k.d_name,
-		   strlen (kbuf->k.d_name) + 1);
-	  kbuf->u.d_type = d_type;
+	  struct dirent64 *source = (struct dirent64 *) p;
+
+	  /* Copy out the fixed-size data.  */
+	  __ino_t ino = source->d_ino;
+	  __off64_t offset = source->d_off;
+	  unsigned int reclen = source->d_reclen;
+	  unsigned char type = source->d_type;
+
+	  /* Check for ino_t overflow.  */
+	  if (__glibc_unlikely (ino != source->d_ino))
+	    return handle_overflow (fd, offset, p - buf);
+
+	  /* Convert to the target layout.  Use a separate struct and
+	     memcpy to side-step aliasing issues.  */
+	  struct __old_dirent64 result;
+	  result.d_ino = ino;
+	  result.d_off = offset;
+	  result.d_reclen = reclen;
+	  result.d_type = type;
+
+	  /* Write the fixed-sized part of the result to the
+	     buffer.  */
+	  size_t result_name_offset = offsetof (struct __old_dirent64, d_name);
+	  memcpy (p, &result, result_name_offset);
+
+	  /* Adjust the position of the name if necessary.  Copy
+	     everything until the end of the record, including the
+	     terminating NUL byte.  */
+	  if (result_name_offset != offsetof (struct dirent64, d_name))
+	    memmove (p + result_name_offset, source->d_name,
+		     reclen - offsetof (struct dirent64, d_name));
 
-	  kbuf = (void *) ((char *) kbuf + kbuf->k.d_reclen);
+	  p += reclen;
 	}
      }
   return retval;