compat getdents64: Use correct offset for retry [BZ #23972]

d_off is the offset of the *next* entry, not the offset of the current
entry.

diff --git a/ChangeLog b/ChangeLog
index 4d57829477469d95da7f552f203b7652cc014e5b..1d21435858ee21148f2ae699b330eb9933ac75b3 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2018-12-10  Florian Weimer  <fweimer@redhat.com>
+
+       [BZ #23972]
+       * sysdeps/unix/sysv/linux/getdents64.c (handle_overflow): Check
+       offset instead of count for clarity.  Fix typo in comment.
+       (__old_getdents64): Keep track of previous offset.  Use it to call
+       handle_overflow.
+       * sysdeps/unix/sysv/linux/tst-readdir64-compat.c (do_test): Check
+       that d_off is never zero.
+
 2018-12-10  Andreas Schwab  <schwab@suse.de>
 
        * sysdeps/unix/sysv/linux/powerpc/powerpc64/*-le.abilist: Move to

diff --git a/sysdeps/unix/sysv/linux/getdents64.c b/sysdeps/unix/sysv/linux/getdents64.c
index bc140b5a7fac3040b2ecb7313b7dd2da05a361c7..46eb5f441986607e2a84235cd5a4139424a2fc89 100644 (file)
--- a/sysdeps/unix/sysv/linux/getdents64.c
+++ b/sysdeps/unix/sysv/linux/getdents64.c
@@ -41,14 +41,14 @@ handle_overflow (int fd, __off64_t offset, ssize_t count)
 {
   /* If this is the first entry in the buffer, we can report the
      error.  */
-  if (count == 0)
+  if (offset == 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..  */
+     will report the error, and return the data read so far.  */
   if (__lseek64 (fd, offset, SEEK_SET) != 0)
     return -1;
   return count;
@@ -70,6 +70,15 @@ __old_getdents64 (int fd, char *buf, size_t nbytes)
   ssize_t retval = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
   if (retval > 0)
     {
+      /* This is the marker for the first entry.  Offset 0 is reserved
+        for the first entry (see rewinddir).  Here, we use it as a
+        marker for the first entry in the buffer.  We never actually
+        seek to offset 0 because handle_overflow reports the error
+        directly, so it does not matter that the offset is incorrect
+        if entries have been read from the descriptor before (so that
+        the descriptor is not actually at offset 0).  */
+      __off64_t previous_offset = 0;
+
       char *p = buf;
       char *end = buf + retval;
       while (p < end)
@@ -84,7 +93,7 @@ __old_getdents64 (int fd, char *buf, size_t nbytes)
 
          /* Check for ino_t overflow.  */
          if (__glibc_unlikely (ino != source->d_ino))
-           return handle_overflow (fd, offset, p - buf);
+           return handle_overflow (fd, previous_offset, p - buf);
 
          /* Convert to the target layout.  Use a separate struct and
             memcpy to side-step aliasing issues.  */
@@ -107,6 +116,7 @@ __old_getdents64 (int fd, char *buf, size_t nbytes)
                     reclen - offsetof (struct dirent64, d_name));
 
          p += reclen;
+         previous_offset = offset;
        }
      }
   return retval;

diff --git a/sysdeps/unix/sysv/linux/tst-readdir64-compat.c b/sysdeps/unix/sysv/linux/tst-readdir64-compat.c
index 43c4a8477c7403c54eb4ac439123ed1683adf1e0..cb78bc9be40e975d3e81b574e4a62f5083d6a5a1 100644 (file)
--- a/sysdeps/unix/sysv/linux/tst-readdir64-compat.c
+++ b/sysdeps/unix/sysv/linux/tst-readdir64-compat.c
@@ -88,6 +88,10 @@ do_test (void)
       else
         TEST_VERIFY_EXIT (entry_test != NULL);
 
+      /* d_off is never zero because it is the offset of the next
+         entry (not the current entry).  */
+      TEST_VERIFY (entry_reference->d_off > 0);
+
       /* Check that the entries are the same.  */
       TEST_COMPARE_BLOB (entry_reference->d_name,
                          strlen (entry_reference->d_name),