[PATCH 25/37] modpost: avoid false-positive file open error

Masahiro Yamada
2020-06-01T05:58:21Z

One problem of grab_file() is that it cannot distinguish the following
two cases:

- It cannot read the file (the file does not exist, or read permission
is not set)

- It can read the file, but the file size is zero

This is because grab_file() calls mmap(), which requires the mapped
length is greater than 0. Hence, grab_file() fails for both cases.

If an empty header file were included for checksum calculation, the
following warning would be printed:

WARNING: modpost: could not open ...: Invalid argument

An empty file is a valid source file, so it should not fail.

Use read_text_file() instead. It can read a zero-length file.
Then, parse_file() will succeed with doing nothing.

Going forward, the first case (it cannot read the file) is a fatal
error. If the source file from which an object was compiled is missing,
something went wrong.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

scripts/mod/sumversion.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/scripts/mod/sumversion.c b/scripts/mod/sumversion.c
index 5fb142db6195..9f77c9dfce20 100644
--- a/scripts/mod/sumversion.c
+++ b/scripts/mod/sumversion.c
@@ -258,9 +258,8 @@ static int parse_file(const char *fname, struct md4_ctx *md)
char *file;
unsigned long i, len;

- file = grab_file(fname, &len);
- if (!file)
- return 0;
+ file = read_text_file(fname);
+ len = strlen(file);

for (i = 0; i < len; i++) {
/* Collapse and ignore \ and CR. */
@@ -287,7 +286,7 @@ static int parse_file(const char *fname, struct md4_ctx *md)

add_char(file[i], md);
}
- release_file(file, len);
+ free(file);
return 1;
}
/* Check whether the file is a static library or not */
--
2.25.1