[PATCH 24/37] modpost: fix potential mmap'ed file overrun in get_src_version()

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

I do not know how reliably this function works, but it looks dangerous
to me.

strchr(sources, '\n');

... continues searching until it finds '\n' or it reaches the '\0'
terminator. In other words, 'sources' should be a null-terminated
string.

However, grab_file() just mmaps a file, so 'sources' is not terminated
with null byte. If the file does not contain '\n' at all, strchr() will
go beyond the mmap'ed memory.

Use read_text_file(), which loads the file content into a malloc'ed
buffer, appending null byte.

Here we are interested only in the first line of *.mod files. Use
get_line() helper to get the first line.

This also makes missing *.mod file a fatal error.

Commit 4be40e22233c ("kbuild: do not emit src version warning for
non-modules") ignored missing *.mod files.

I do not fully understand what that commit addressed, but commit
91341d4b2c19 ("kbuild: introduce new option to enhance section mismatch
analysis") introduced partial section checks by using modpost. built-in.o
was parsed by modpost. Even modules had a problem because *.mod files
were created after the modpost check.

Commit b7dca6dd1e59 ("kbuild: create *.mod with full directory path and
remove MODVERDIR") stopped doing that. Now that modpost is only invoked
after the directory descend, *.mod files should always exist at the
modpost stage.

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

scripts/mod/sumversion.c | 28 +++++++++++-----------------
1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/scripts/mod/sumversion.c b/scripts/mod/sumversion.c
index f27f22420cbc..5fb142db6195 100644
--- a/scripts/mod/sumversion.c
+++ b/scripts/mod/sumversion.c
@@ -392,40 +392,34 @@ static int parse_source_files(const char *objfile, struct md4_ctx *md)
/* Calc and record src checksum. */
void get_src_version(const char *modname, char sum[], unsigned sumlen)
{
- void *file;
- unsigned long len;
+ char *buf, *pos, *firstline;
struct md4_ctx md;
- char *sources, *end, *fname;
+ char *fname;
char filelist[PATH_MAX + 1];

/* objects for a module are listed in the first line of *.mod file. */
snprintf(filelist, sizeof(filelist), "%.*smod",
(int)strlen(modname) - 1, modname);

- file = grab_file(filelist, &len);
- if (!file)
- /* not a module or .mod file missing - ignore */
- return;
+ buf = read_text_file(filelist);

- sources = file;
-
- end = strchr(sources, '\n');
- if (!end) {
+ pos = buf;
+ firstline = get_line(&pos);
+ if (!firstline) {
warn("bad ending versions file for %s\n", modname);
- goto release;
+ goto free;
}
- *end = '\0';

md4_init(&md);
- while ((fname = strsep(&sources, " ")) != NULL) {
+ while ((fname = strsep(&firstline, " "))) {
if (!*fname)
continue;
if (!(is_static_library(fname)) &&
!parse_source_files(fname, &md))
- goto release;
+ goto free;
}

md4_final_ascii(&md, sum, sumlen);
-release:
- release_file(file, len);
+free:
+ free(buf);
}
--
2.25.1