[PATCH v3] fixdep: exit with error code in error branches of do_config_file()

[Lukas Bulwahn <lukas.bulwahn@gmail.com>]

do_config_file() should exit with an error code on internal run-time
errors, and not return if it fails as then the error in do_config_file()
would go unnoticed in the current code and allow the build to continue.
The exit with error code will make the build fail in those very
exceptional cases. If this occurs, this actually indicates a deeper
problem in the execution of the kernel build process.

Now, in these error cases, we do not explicitly free memory and close
the file handlers in do_config_file(), as this is covered by exit().

This issue in the fixdep script was introduced with its initial
implementation back in 2002 by the original author Kai Germaschewski with
this commit 04bd72170653 ("kbuild: Make dependencies at compile time")
in the linux history git tree, i.e.,
git://git.kernel.org/pub/scm/linux/kernel/git/history/history.git.

This issue was identified during the review of a previous patch that
intended to address a memory leak detected by a static analysis tool.

Link: https://lkml.org/lkml/2017/12/14/736

Suggested-by: Nicholas Mc Guire <der.herr@hofr.at>
Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
---
compile tested on top of next-20180108 with clang and gcc
Changes in v2:
  - no code change; only include proper Fixes tag and explain it
Changes in v3:
  - Clarify history commit reference and dropped Fixes tag
  - Do not error on empty files (reverts one hunk of v2)

 scripts/basic/fixdep.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index bbf62cb..86a61d6 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -290,13 +290,11 @@ static void do_config_file(const char *filename)
 	map = malloc(st.st_size + 1);
 	if (!map) {
 		perror("fixdep: malloc");
-		close(fd);
-		return;
+		exit(2);
 	}
 	if (read(fd, map, st.st_size) != st.st_size) {
 		perror("fixdep: read");
-		close(fd);
-		return;
+		exit(2);
 	}
 	map[st.st_size] = '\0';
 	close(fd);
-- 
2.5.5