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echo: do not assume that free() leaves errno unmodified

musl libc's mallocng free() may modify errno if kernel does not support
MADV_FREE which causes echo to echo with error when it shouldn't.

Future versions of POSIX[1] will require that free() leaves errno
unmodified but til then, do not rely free() implementation.

Should fix downstream issues:
https://github.com/alpinelinux/docker-alpine/issues/134
https://gitlab.alpinelinux.org/alpine/aports/-/issues/12311

Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Natanael Copa 3 years ago
parent
commit
e880c9c100
1 changed files with 5 additions and 5 deletions
  1. 5 5
      coreutils/echo.c

+ 5 - 5
coreutils/echo.c

@@ -97,6 +97,7 @@ int echo_main(int argc UNUSED_PARAM, char **argv)
 #else
 	char nflag = 1;
 	char eflag = 0;
+	int err;
 
 	while ((arg = *++argv) != NULL) {
 		char n, e;
@@ -185,13 +186,12 @@ int echo_main(int argc UNUSED_PARAM, char **argv)
  do_write:
 	/* Careful to error out on partial writes too (think ENOSPC!) */
 	errno = 0;
-	/*r =*/ full_write(STDOUT_FILENO, buffer, out - buffer);
-	free(buffer);
-	if (/*WRONG:r < 0*/ errno) {
+	err = full_write(STDOUT_FILENO, buffer, out - buffer) != out - buffer;
+	if (err) {
 		bb_simple_perror_msg(bb_msg_write_error);
-		return 1;
 	}
-	return 0;
+	free(buffer);
+	return err;
 }
 
 /*