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List:       glibc-cvs
Subject:    [glibc/azanella/bz23960-dirent] linux: Use getdents64 on non-LFS readdir
From:       Adhemerval Zanella via Glibc-cvs <glibc-cvs () sourceware ! org>
Date:       2023-01-27 20:39:49
Message-ID: 20230127203949.C53F73858416 () sourceware ! org
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b18673fbcfa7b467fec409dbf2276fb7bb8bdcdf

commit b18673fbcfa7b467fec409dbf2276fb7bb8bdcdf
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Tue Oct 20 13:37:15 2020 -0300

    linux: Use getdents64 on non-LFS readdir
    
    The non-LFS opendir reserves a translation entry to be used to return
    the entry and the dirent64 struct is translated to the temporary buffer
    on each readdir call.
    
    Entries that overflow d_off/d_ino and the buffer reallocation failure
    (in case of large d_name) are ignored.
    
    Checked on x86_64-linux-gnu and i686-linux-gnu.

Diff:
---
 dirent/tst-scandir.c                |  6 ++-
 include/dirent.h                    |  2 +-
 sysdeps/unix/sysv/linux/dirstream.h |  5 +++
 sysdeps/unix/sysv/linux/readdir.c   | 83 +++++++++++++++++++++++++------------
 4 files changed, 67 insertions(+), 29 deletions(-)

diff --git a/dirent/tst-scandir.c b/dirent/tst-scandir.c
index 8d87d4dd74..7bc666449e 100644
--- a/dirent/tst-scandir.c
+++ b/dirent/tst-scandir.c
@@ -155,8 +155,12 @@ do_test (void)
     }
   if (n != 6)
     {
+      /* Non-lfs opendir skips entries that can not be represented (for
+	 instance if d_off is not an offset but rather an internal filesystem
+	 representation.  For this case there is no point in continue the
+	 testcase.  */
       printf ("scandir returned %d entries instead of 6\n", n);
-      return 1;
+      return EXIT_UNSUPPORTED;
     }
 
   struct
diff --git a/include/dirent.h b/include/dirent.h
index d7567f5e86..17827176ba 100644
--- a/include/dirent.h
+++ b/include/dirent.h
@@ -1,8 +1,8 @@
 #ifndef _DIRENT_H
+# include <dirent/dirent.h>
 # ifndef _ISOMAC
 #  include <dirstream.h>
 # endif
-# include <dirent/dirent.h>
 # ifndef _ISOMAC
 # include <sys/stat.h>
 # include <stdbool.h>
diff --git a/sysdeps/unix/sysv/linux/dirstream.h b/sysdeps/unix/sysv/linux/dirstream.h
index 3cb313b410..adcf8234f1 100644
--- a/sysdeps/unix/sysv/linux/dirstream.h
+++ b/sysdeps/unix/sysv/linux/dirstream.h
@@ -18,6 +18,7 @@
 #ifndef	_DIRSTREAM_H
 #define	_DIRSTREAM_H	1
 
+#include <dirent.h>
 #include <sys/types.h>
 
 #include <libc-lock.h>
@@ -41,6 +42,10 @@ struct __dirstream
 
     int errcode;		/* Delayed error code.  */
 
+#if !defined __OFF_T_MATCHES_OFF64_T || !defined __INO_T_MATCHES_INO64_T
+    struct dirent tdp;
+#endif
+
     /* Directory block.  We must make sure that this block starts
        at an address that is aligned adequately enough to store
        dirent entries.  Using the alignment of "void *" is not
diff --git a/sysdeps/unix/sysv/linux/readdir.c b/sysdeps/unix/sysv/linux/readdir.c
index 4a4c00ea07..cd0ccaf33a 100644
--- a/sysdeps/unix/sysv/linux/readdir.c
+++ b/sysdeps/unix/sysv/linux/readdir.c
@@ -21,42 +21,71 @@
 #if !_DIRENT_MATCHES_DIRENT64
 #include <dirstream.h>
 
+/* Translate the DP64 entry to the non-LFS one in the translation entry
+   at dirstream DS.  Return true is the translation was possible or
+   false if either an internal field can not be represented in the non-LFS
+   entry or if the name is too long.  */
+static bool
+dirstream_entry (struct __dirstream *ds, const struct dirent64 *dp64)
+{
+  /* Check for overflow.  */
+  if (!in_off_t_range (dp64->d_off) || !in_ino_t_range (dp64->d_ino))
+    return false;
+
+  /* And if name is too large.  */
+  if (dp64->d_reclen - offsetof (struct dirent64, d_name) > NAME_MAX)
+    return false;
+
+  ds->filepos = dp64->d_off;
+
+  ds->tdp.d_off = dp64->d_off;
+  ds->tdp.d_ino = dp64->d_ino;
+  ds->tdp.d_reclen = sizeof (struct dirent)
+    + dp64->d_reclen - offsetof (struct dirent64, d_name);
+  ds->tdp.d_type = dp64->d_type;
+  memcpy (ds->tdp.d_name, dp64->d_name,
+	  dp64->d_reclen - offsetof (struct dirent64, d_name));
+
+  return true;
+}
+
 /* Read a directory entry from DIRP.  */
 struct dirent *
 __readdir_unlocked (DIR *dirp)
 {
-  struct dirent *dp;
   int saved_errno = errno;
 
-  if (dirp->offset >= dirp->size)
+  while (1)
     {
-      /* We've emptied out our buffer.  Refill it.  */
-
-      size_t maxread = dirp->allocation;
-      ssize_t bytes;
-
-      bytes = __getdents (dirp->fd, dirp->data, maxread);
-      if (bytes <= 0)
+      if (dirp->offset >= dirp->size)
 	{
-	  /* Linux may fail with ENOENT on some file systems if the
-	     directory inode is marked as dead (deleted).  POSIX
-	     treats this as a regular end-of-directory condition, so
-	     do not set errno in that case, to indicate success.  */
-	  if (bytes == 0 || errno == ENOENT)
-	    __set_errno (saved_errno);
-	  return NULL;
-	}
-      dirp->size = (size_t) bytes;
-
-      /* Reset the offset into the buffer.  */
-      dirp->offset = 0;
+	  /* We've emptied out our buffer.  Refill it.  */
+	  ssize_t bytes = __getdents64 (dirp->fd, dirp->data,
+					dirp->allocation);
+	  if (bytes <= 0)
+	    {
+	      /* Linux may fail with ENOENT on some file systems if the
+		 directory inode is marked as dead (deleted).  POSIX
+		 treats this as a regular end-of-directory condition, so
+		 do not set errno in that case, to indicate success.  */
+	      if (bytes < 0 && errno == ENOENT)
+		__set_errno (saved_errno);
+	      return NULL;
+	    }
+	  dirp->size = bytes;
+
+ 	  /* Reset the offset into the buffer.  */
+	  dirp->offset = 0;
+ 	}
+
+      struct dirent64 *dp64 = (struct dirent64 *) &dirp->data[dirp->offset];
+      dirp->offset += dp64->d_reclen;
+
+      /* Skip entries which might overflow d_off/d_ino or if the translation
+	 buffer can not be resized.  */
+      if (dirstream_entry (dirp, dp64))
+	return &dirp->tdp;
     }
-
-  dp = (struct dirent *) &dirp->data[dirp->offset];
-  dirp->offset += dp->d_reclen;
-  dirp->filepos = dp->d_off;
-
-  return dp;
 }
 
 struct dirent *
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