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libio: Add terminating NUL when the first character is EOF in getdelim [BZ #28038]

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POSIX requires that the buffer used by getdelim/getline add a
terminating NUL whenever an EOF is read.

* libio/iogetdelim.c (__getdelim): Add a NUL byte when the first
__underflow is called.
* libio/tst-getdelim.c (do_test): Add a test case for the bug.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
Collin Funk
2025-10-08 20:10:44 -07:00
parent 5a83a403d1
commit 33eff78c8b
2 changed files with 18 additions and 0 deletions
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1
libio/iogetdelim.c
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@@ -77,6 +77,7 @@ __getdelim (char **lineptr, size_t *n, int delimiter, FILE *fp)
if (__underflow (fp) == EOF)
{
result = -1;
(*lineptr)[0] = '\0';
goto unlock_return;
}
len = fp->_IO_read_end - fp->_IO_read_ptr;

17
libio/tst-getdelim.c
View File

@@ -27,6 +27,7 @@
#include <support/support.h>
#include <support/test-driver.h>
#include <support/xstdio.h>
#include <support/temp_file.h>
static int
do_test (void)
@@ -50,6 +51,22 @@ do_test (void)
xfclose (memstream);
free (lineptr);
/* Test that getdelim NUL terminates upon reading an EOF from an empty
file (BZ #28038). This test fails on glibc 2.42 and earlier. */
lineptr = xmalloc (1);
lineptr[0] = 'A';
linelen = 1;
char *file_name;
TEST_VERIFY_EXIT (create_temp_file ("tst-getdelim.", &file_name) != -1);
FILE *fp = fopen (file_name, "r");
TEST_VERIFY_EXIT (fp != NULL);
TEST_VERIFY (getdelim (&lineptr, &linelen, '\n', fp) == -1);
TEST_VERIFY (linelen > 0);
TEST_VERIFY (lineptr[0] == '\0');
fclose (fp);
free (file_name);
free (lineptr);
return 0;
}