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ftell: seek to end only when there are unflushed bytes (BZ #17647)

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Currently we seek to end of file if there are unflushed writes or the
stream is in write mode, to get the current offset for writing in
append mode, which is the end of file.  The latter case (i.e. stream
is in write mode, but no unflushed writes) is unnecessary since it
will only happen when the stream has just been flushed, in which case
the recorded offset ought to be reliable.

Removing that case lets ftell give the correct offset when it follows
an ftruncate.  The latter truncates the file, but does not change the
file position, due to which it is permissible to call ftell without an
intervening fseek call.

Tested on x86_64 to verify that the added test case fails without the
patch and succeeds with it, and that there are no additional
regressions due to it.

	[BZ #17647]
	* libio/fileops.c (do_ftell): Seek only when there are
	unflushed writes.
	* libio/wfileops.c (do_ftell_wide): Likewise.
	* libio/tst-ftell-active-handler.c (do_ftruncate_test): New
	test case.
	(do_one_test): Call it.
This commit is contained in:
Siddhesh Poyarekar 2014-12-04 08:08:37 +05:30
parent e3d6dba5df
commit be349d7042
5 changed files with 108 additions and 10 deletions
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10
ChangeLog
View File

@ -1,3 +1,13 @@
2914-12-04 Siddhesh Poyarekar <siddhesh@redhat.com>
[BZ #17647]
* libio/fileops.c (do_ftell): Seek only when there are
unflushed writes.
* libio/wfileops.c (do_ftell_wide): Likewise.
* libio/tst-ftell-active-handler.c (do_ftruncate_test): New
test case.
(do_one_test): Call it.
2014-12-03 Joseph Myers <joseph@codesourcery.com>
* conform/list-header-symbols.pl (%extra_syms): Add getdate_err

2
NEWS
View File

@ -13,7 +13,7 @@ Version 2.21
16619, 16740, 16857, 17192, 17266, 17344, 17363, 17370, 17371, 17411,
17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555, 17570, 17571,
17572, 17573, 17574, 17581, 17582, 17583, 17584, 17585, 17589, 17594,
17601, 17608, 17616, 17625, 17633, 17664, 17665, 17668.
17601, 17608, 17616, 17625, 17633, 17647, 17664, 17665, 17668.
* CVE-2104-7817 The wordexp function could ignore the WRDE_NOCMD flag
under certain input conditions resulting in the execution of a shell for

7
libio/fileops.c
View File

@ -943,15 +943,14 @@ do_ftell (_IO_FILE *fp)
yet. */
if (fp->_IO_buf_base != NULL)
{
bool was_writing = (fp->_IO_write_ptr > fp->_IO_write_base
|| _IO_in_put_mode (fp));
bool unflushed_writes = fp->_IO_write_ptr > fp->_IO_write_base;
bool append_mode = (fp->_flags & _IO_IS_APPENDING) == _IO_IS_APPENDING;
/* When we have unflushed writes in append mode, seek to the end of the
file and record that offset. This is the only time we change the file
stream state and it is safe since the file handle is active. */
if (was_writing && append_mode)
if (unflushed_writes && append_mode)
{
result = _IO_SYSSEEK (fp, 0, _IO_seek_end);
if (result == _IO_pos_BAD)
@ -961,7 +960,7 @@ do_ftell (_IO_FILE *fp)
}
/* Adjust for unflushed data. */
if (!was_writing)
if (!unflushed_writes)
offset -= fp->_IO_read_end - fp->_IO_read_ptr;
/* We don't trust _IO_read_end to represent the current file offset when
writing in append mode because the value would have to be shifted to

90
libio/tst-ftell-active-handler.c
View File

@ -88,6 +88,95 @@ static size_t file_len;
typedef int (*fputs_func_t) (const void *data, FILE *fp);
fputs_func_t fputs_func;
/* This test verifies that the offset reported by ftell is correct after the
file is truncated using ftruncate. ftruncate does not change the file
offset on truncation and hence, SEEK_CUR should continue to point to the
old offset and not be changed to the new offset. */
static int
do_ftruncate_test (const char *filename)
{
FILE *fp = NULL;
int fd;
int ret = 0;
struct test
{
const char *mode;
int fd_mode;
} test_modes[] = {
{"r+", O_RDWR},
{"w", O_WRONLY},
{"w+", O_RDWR},
{"a", O_WRONLY},
{"a+", O_RDWR}
};
for (int j = 0; j < 2; j++)
{
for (int i = 0; i < sizeof (test_modes) / sizeof (struct test); i++)
{
int fileret;
printf ("\tftruncate: %s (file, \"%s\"): ",
j == 0 ? "fopen" : "fdopen",
test_modes[i].mode);
if (j == 0)
fileret = get_handles_fopen (filename, fd, fp, test_modes[i].mode);
else
fileret = get_handles_fdopen (filename, fd, fp,
test_modes[i].fd_mode,
test_modes[i].mode);
if (fileret != 0)
return fileret;
/* Write some data. */
size_t written = fputs_func (data, fp);
if (written == EOF)
{
printf ("fputs[1] failed to write data\n");
ret |= 1;
}
/* Record the offset. */
long offset = ftell (fp);
/* Flush data to allow switching active handles. */
if (fflush (fp))
{
printf ("Flush failed: %m\n");
ret |= 1;
}
/* Now truncate the file. */
if (ftruncate (fd, 0) != 0)
{
printf ("Failed to truncate file: %m\n");
ret |= 1;
}
/* ftruncate does not change the offset, so there is no need to call
anything to be able to switch active handles. */
long new_offset = ftell (fp);
/* The offset should remain unchanged since ftruncate does not update
it. */
if (offset != new_offset)
{
printf ("Incorrect offset. Expected %zu, but got %ld\n",
offset, new_offset);
ret |= 1;
}
else
printf ("offset = %ld\n", offset);
fclose (fp);
}
}
return ret;
}
/* Test that ftell output after a rewind is correct. */
static int
do_rewind_test (const char *filename)
@ -481,6 +570,7 @@ do_one_test (const char *filename)
ret |= do_write_test (filename);
ret |= do_append_test (filename);
ret |= do_rewind_test (filename);
ret |= do_ftruncate_test (filename);
return ret;
}

9
libio/wfileops.c
View File

@ -626,16 +626,15 @@ do_ftell_wide (_IO_FILE *fp)
const wchar_t *wide_read_base;
const wchar_t *wide_read_ptr;
const wchar_t *wide_read_end;
bool was_writing = ((fp->_wide_data->_IO_write_ptr
> fp->_wide_data->_IO_write_base)
|| _IO_in_put_mode (fp));
bool unflushed_writes = (fp->_wide_data->_IO_write_ptr
> fp->_wide_data->_IO_write_base);
bool append_mode = (fp->_flags & _IO_IS_APPENDING) == _IO_IS_APPENDING;
/* When we have unflushed writes in append mode, seek to the end of the
file and record that offset. This is the only time we change the file
stream state and it is safe since the file handle is active. */
if (was_writing && append_mode)
if (unflushed_writes && append_mode)
{
result = _IO_SYSSEEK (fp, 0, _IO_seek_end);
if (result == _IO_pos_BAD)
@ -674,7 +673,7 @@ do_ftell_wide (_IO_FILE *fp)
struct _IO_codecvt *cv = fp->_codecvt;
int clen = (*cv->__codecvt_do_encoding) (cv);
if (!was_writing)
if (!unflushed_writes)
{
if (clen > 0)
{