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libio: Synthesize ESPIPE error if lseek returns 0 after reading bytes

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This is required so that fclose, when trying to seek to the right
position after filling the input buffer, does not fail with EINVAL.
This fclose code path only ignores ESPIPE errors.

Reported by Petr Pisar on
<https://bugzilla.redhat.com/show_bug.cgi?id=2358265>.

Fixes commit be6818be31e756398e45f70e2819d78be0961223 ("Make fclose
seek input file to right offset (bug 12724)").

Reviewed-by: Frédéric Bérat <fberat@redhat.com>
This commit is contained in:
Florian Weimer 2025-04-08 18:38:38 +02:00
parent de14f1959e
commit 7b47b3dd21
3 changed files with 61 additions and 0 deletions
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10
libio/fileops.c
View File

@ -928,6 +928,16 @@ do_ftell (FILE *fp)
if (result == EOF)
return result;
if (result == 0 && offset < 0)
{
/* This happens for some character devices that always report
file offset 0 even after some data has been read (instead of
failing with ESPIPE). The fclose path ignores this
error. */
__set_errno (ESPIPE);
return EOF;
}
result += offset;
if (result < 0)

1
stdio-common/Makefile
View File

@ -262,6 +262,7 @@ tests := \
tst-bz11319-fortify2 \
tst-cookie \
tst-dprintf-length \
tst-fclose-devzero \
tst-fclose-offset \
tst-fdopen \
tst-fdopen2 \

50
stdio-common/tst-fclose-devzero.c Normal file
View File

@ -0,0 +1,50 @@
/* Test that always-zero lseek does not cause fclose failure after fread.
Copyright (C) 2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <support/check.h>
#include <support/xstdio.h>
int
do_test (void)
{
for (int do_ftello = 0; do_ftello < 2; ++do_ftello)
{
FILE *fp = xfopen ("/dev/zero", "r");
char buf[17];
memset (buf, 0xcc, sizeof (buf));
xfread (buf, 1, sizeof (buf), fp);
static const char zeros[sizeof (buf)] = { 0 };
TEST_COMPARE_BLOB (buf, sizeof (buf), zeros, sizeof (zeros));
if (do_ftello)
{
errno = 0;
TEST_COMPARE (ftello (fp), -1);
TEST_COMPARE (errno, ESPIPE);
}
/* Do not use xfclose because it flushes first. */
TEST_COMPARE (fclose (fp), 0);
}
return 0;
}
#include <support/test-driver.c>