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[RFA]: race safe fwalk
- From: Thomas Pfaff <tpfaff at gmx dot net>
- To: newlib at sources dot redhat dot com
- Date: Mon, 08 Mar 2004 21:24:59 +0100
- Subject: [RFA]: race safe fwalk
This time with attachment.
There is a possible race between fwalk and fopen:
When a thread make a call to fopen the FILE * _flags will be set to 1 in
findfp to mark it used and later it will be changed to the real FILE flag.
When another thread calls fwalk during that time fwalk will treat the
FILE as already opened and calls the callback functions with the yet
unopened and only partially initialized FILE *.
This can be avoided by checking for fp->_flags != 0 && fp->_flags != 1.
Since _flags is signed short i did not check for _flags > 1. The flag
should be set as the last step in an open call.
I do not think that 1 is a valid _flag for an open file. Correct me if
am wrong.
2004-03-08 Thomas Pfaff <tpfaff@gmx.net>
* libc/stdio/fdopen.c (_fdopen_r): Add missing
__lock_init_recursive.
Set FILE flags as the last step.
* libc/stdio/fopen.c (_fopen_r): Set FILE flags as the last
step.
* libc/stdio/fwalk.c: Check for _flags != 1 to make sure that
file is really open.
* libc/stdio64/fdopen64.c (_fdopen64_r): Set FILE flags as the
last step.
* libc/stdio64/fopen64.c (_fopen64_r): Ditto.
Index: stdio/fdopen.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio/fdopen.c,v
retrieving revision 1.6
diff -u -p -r1.6 fdopen.c
--- stdio/fdopen.c 19 Sep 2002 21:28:52 -0000 1.6
+++ stdio/fdopen.c 8 Mar 2004 20:01:06 -0000
@@ -76,18 +76,7 @@ _DEFUN (_fdopen_r, (ptr, fd, mode),
if ((fp = __sfp (ptr)) == 0)
return 0;
- fp->_flags = flags;
- /*
- * If opened for appending, but underlying descriptor
- * does not have O_APPEND bit set, assert __SAPP so that
- * __swrite() will lseek to end before each write.
- */
- if ((oflags & O_APPEND)
-#ifdef HAVE_FCNTL
- && !(fdflags & O_APPEND)
-#endif
- )
- fp->_flags |= __SAPP;
+
fp->_file = fd;
fp->_cookie = (_PTR) fp;
@@ -100,7 +89,21 @@ _DEFUN (_fdopen_r, (ptr, fd, mode),
fp->_write = __swrite;
fp->_seek = __sseek;
fp->_close = __sclose;
-
+#ifndef __SINGLE_THREAD__
+ __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
+#endif
+ fp->_flags = flags;
+ /*
+ * If opened for appending, but underlying descriptor
+ * does not have O_APPEND bit set, assert __SAPP so that
+ * __swrite() will lseek to end before each write.
+ */
+ if ((oflags & O_APPEND)
+#ifdef HAVE_FCNTL
+ && !(fdflags & O_APPEND)
+#endif
+ )
+ fp->_flags |= __SAPP;
#ifdef __SCLE
/* Explicit given mode results in explicit setting mode on fd */
if (oflags & O_BINARY)
Index: stdio/fopen.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio/fopen.c,v
retrieving revision 1.5
diff -u -p -r1.5 fopen.c
--- stdio/fopen.c 22 Aug 2003 18:52:25 -0000 1.5
+++ stdio/fopen.c 8 Mar 2004 20:01:07 -0000
@@ -143,12 +143,15 @@ _DEFUN (_fopen_r, (ptr, file, mode),
}
fp->_file = f;
- fp->_flags = flags;
fp->_cookie = (_PTR) fp;
fp->_read = __sread;
fp->_write = __swrite;
fp->_seek = __sseek;
fp->_close = __sclose;
+#ifndef __SINGLE_THREAD__
+ __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
+#endif
+ fp->_flags = flags;
if (fp->_flags & __SAPP)
_fseek_r (ptr, fp, 0, SEEK_END);
@@ -156,10 +159,6 @@ _DEFUN (_fopen_r, (ptr, file, mode),
#ifdef __SCLE
if (__stextmode (fp->_file))
fp->_flags |= __SCLE;
-#endif
-
-#ifndef __SINGLE_THREAD__
- __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
#endif
return fp;
Index: stdio/fwalk.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio/fwalk.c,v
retrieving revision 1.3
diff -u -p -r1.3 fwalk.c
--- stdio/fwalk.c 31 Jan 2004 00:39:07 -0000 1.3
+++ stdio/fwalk.c 8 Mar 2004 20:01:07 -0000
@@ -40,14 +40,14 @@ _fwalk (ptr, function)
{
for (g = &ptr->__sglue; g != NULL; g = g->_next)
for (fp = g->_iobs, n = g->_niobs; --n >= 0; fp++)
- if (fp->_flags != 0)
+ if (fp->_flags != 0 && fp->_flags != 1)
ret |= (*function) (fp);
}
/* Must traverse global list for all other streams. */
for (g = &_GLOBAL_REENT->__sglue; g != NULL; g = g->_next)
for (fp = g->_iobs, n = g->_niobs; --n >= 0; fp++)
- if (fp->_flags != 0)
+ if (fp->_flags != 0 && fp->_flags != 1)
ret |= (*function) (fp);
return ret;
Index: stdio64/fdopen64.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio64/fdopen64.c,v
retrieving revision 1.2
diff -u -p -r1.2 fdopen64.c
--- stdio64/fdopen64.c 25 Jul 2003 16:19:55 -0000 1.2
+++ stdio64/fdopen64.c 8 Mar 2004 20:01:07 -0000
@@ -63,18 +63,6 @@ _DEFUN (_fdopen64_r, (ptr, fd, mode),
if ((fp = __sfp (ptr)) == 0)
return 0;
- fp->_flags = flags;
- /*
- * If opened for appending, but underlying descriptor
- * does not have O_APPEND bit set, assert __SAPP so that
- * __swrite() will lseek to end before each write.
- */
- if ((oflags & O_APPEND)
-#ifdef HAVE_FCNTL
- && !(fdflags & O_APPEND)
-#endif
- )
- fp->_flags |= __SAPP;
fp->_file = fd;
fp->_cookie = (_PTR) fp;
@@ -89,6 +77,21 @@ _DEFUN (_fdopen64_r, (ptr, fd, mode),
fp->_seek64 = __sseek64;
fp->_close = __sclose;
+#ifndef __SINGLE_THREAD__
+ __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
+#endif
+ fp->_flags = flags;
+ /*
+ * If opened for appending, but underlying descriptor
+ * does not have O_APPEND bit set, assert __SAPP so that
+ * __swrite() will lseek to end before each write.
+ */
+ if ((oflags & O_APPEND)
+#ifdef HAVE_FCNTL
+ && !(fdflags & O_APPEND)
+#endif
+ )
+ fp->_flags |= __SAPP;
#ifdef __SCLE
/* Explicit given mode results in explicit setting mode on fd */
if (oflags & O_BINARY)
@@ -99,9 +102,6 @@ _DEFUN (_fdopen64_r, (ptr, fd, mode),
fp->_flags |= __SCLE;
#endif
-#ifndef __SINGLE_THREAD__
- __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
-#endif
fp->_flags |= __SL64;
Index: stdio64/fopen64.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio64/fopen64.c,v
retrieving revision 1.4
diff -u -p -r1.4 fopen64.c
--- stdio64/fopen64.c 22 Aug 2003 18:52:25 -0000 1.4
+++ stdio64/fopen64.c 8 Mar 2004 20:01:07 -0000
@@ -96,13 +96,17 @@ _DEFUN (_fopen64_r, (ptr, file, mode),
}
fp->_file = f;
- fp->_flags = flags;
fp->_cookie = (_PTR) fp;
fp->_read = __sread;
fp->_write = __swrite64;
fp->_seek = __sseek;
fp->_seek64 = __sseek64;
fp->_close = __sclose;
+#ifndef __SINGLE_THREAD__
+ __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
+#endif
+
+ fp->_flags = flags;
if (fp->_flags & __SAPP)
_fseeko64_r (ptr, fp, 0, SEEK_END);
@@ -113,10 +117,6 @@ _DEFUN (_fopen64_r, (ptr, file, mode),
#endif
fp->_flags |= __SL64;
-
-#ifndef __SINGLE_THREAD__
- __lock_init_recursive (*(_LOCK_RECURSIVE_T *)&fp->_lock);
-#endif
return fp;
}