From: Shaun Ruffell <sruffell@sruffell.net>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Jessica Yu <jeyu@kernel.org>,
Matthias Maennich <maennich@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kbuild@vger.kernel.org,
Michal Marek <michal.lkml@markovi.net>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/6] modpost: fix broken sym->namespace for external module builds
Date: Thu, 3 Oct 2019 01:29:27 -0500 [thread overview]
Message-ID: <20191003062927.4pusu3sfjyfayigy@sruffell.net> (raw)
In-Reply-To: <20191003075826.7478-3-yamada.masahiro@socionext.com>
On Thu, Oct 03, 2019 at 04:58:22PM +0900, Masahiro Yamada wrote:
> Currently, external module builds produce tons of false-positives:
>
> WARNING: module <mod> uses symbol <sym> from namespace <ns>, but does not import it.
>
> Here, the <ns> part shows a random string.
>
> When you build external modules, the symbol info of vmlinux and
> in-kernel modules are read from $(objtree)/Module.symvers, but
> read_dump() is buggy in multiple ways:
>
> [1] When the modpost is run for vmlinux and in-kernel modules,
> sym_extract_namespace() allocates memory for the namespace. On the
> other hand, read_dump() does not, then sym->namespace will point to
> somewhere in the line buffer of get_next_line(). The data in the
> buffer will be replaced soon, and sym->namespace will end up with
> pointing to unrelated data. As a result, check_exports() will show
> random strings in the warning messages.
>
> [2] When there is no namespace, sym_extract_namespace() returns NULL.
> On the other hand, read_dump() sets namespace to an empty string "".
> (but, it will be later replaced with unrelated data due to bug [1].)
> The check_exports() shows a warning unless exp->namespace is NULL,
> so every symbol read from read_dump() emits the warning, which is
> mostly false positive.
>
> To address [1], sym_add_exported() calls strdup() for s->namespace.
> The namespace from sym_extract_namespace() must be freed to avoid
> memory leak.
>
> For [2], I changed the if-conditional in check_exports().
>
> This commit also fixes sym_add_exported() to set s->namespace correctly
> when the symbol is preloaded.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Reviewed-by: Matthias Maennich <maennich@google.com>
> ---
>
> Changes in v2:
> - Change the approach to deal with ->preloaded
>
> scripts/mod/modpost.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 2c644086c412..936d3ad23c83 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -166,7 +166,7 @@ struct symbol {
> struct module *module;
> unsigned int crc;
> int crc_valid;
> - const char *namespace;
> + char *namespace;
> unsigned int weak:1;
> unsigned int vmlinux:1; /* 1 if symbol is defined in vmlinux */
> unsigned int kernel:1; /* 1 if symbol is from kernel
> @@ -348,7 +348,7 @@ static enum export export_from_sec(struct elf_info *elf, unsigned int sec)
> return export_unknown;
> }
>
> -static const char *sym_extract_namespace(const char **symname)
> +static char *sym_extract_namespace(const char **symname)
> {
> char *namespace = NULL;
> char *ns_separator;
> @@ -373,7 +373,6 @@ static struct symbol *sym_add_exported(const char *name, const char *namespace,
>
> if (!s) {
> s = new_symbol(name, mod, export);
> - s->namespace = namespace;
> } else {
> if (!s->preloaded) {
> warn("%s: '%s' exported twice. Previous export was in %s%s\n",
> @@ -384,6 +383,8 @@ static struct symbol *sym_add_exported(const char *name, const char *namespace,
> s->module = mod;
> }
> }
> + free(s->namespace);
> + s->namespace = namespace ? strdup(namespace) : NULL;
> s->preloaded = 0;
> s->vmlinux = is_vmlinux(mod->name);
> s->kernel = 0;
> @@ -670,7 +671,8 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
> unsigned int crc;
> enum export export;
> bool is_crc = false;
> - const char *name, *namespace;
> + const char *name;
> + char *namespace;
>
> if ((!is_vmlinux(mod->name) || mod->is_dot_o) &&
> strstarts(symname, "__ksymtab"))
> @@ -745,6 +747,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
> name = symname + strlen("__ksymtab_");
> namespace = sym_extract_namespace(&name);
> sym_add_exported(name, namespace, mod, export);
> + free(namespace);
> }
> if (strcmp(symname, "init_module") == 0)
> mod->has_init = 1;
> @@ -2193,7 +2196,7 @@ static int check_exports(struct module *mod)
> else
> basename = mod->name;
>
> - if (exp->namespace) {
> + if (exp->namespace && exp->namespace[0]) {
> add_namespace(&mod->required_namespaces,
> exp->namespace);
>
This looks good to me and is better than what I had originally proposed.
I confirmed that I can still build an external module without any
warnings. (But I did have to convince myself that it was OK to store
empty namespace strings in the symbol structure and that check_exports()
would cover it sufficiently)
If you would like, feel free to add my
Reviewed-by: Shaun Ruffell <sruffell@sruffell.net>
or
Tested-by: Shaun Ruffell <sruffell@sruffell.net>
next prev parent reply other threads:[~2019-10-03 13:29 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 7:58 [PATCH v2 0/6] module: various bug-fixes and clean-ups for module namespace Masahiro Yamada
2019-10-03 7:58 ` [PATCH v2 1/6] module: swap the order of symbol.namespace Masahiro Yamada
2019-10-03 7:58 ` [PATCH v2 2/6] modpost: fix broken sym->namespace for external module builds Masahiro Yamada
2019-10-03 6:29 ` Shaun Ruffell [this message]
2019-10-03 14:42 ` Masahiro Yamada
2019-10-04 15:10 ` Jessica Yu
2019-10-03 7:58 ` [PATCH v2 3/6] module: rename __kstrtab_ns_* to __kstrtabns_* to avoid symbol conflict Masahiro Yamada
2019-10-03 7:58 ` [PATCH v2 4/6] kbuild: fix build error of 'make nsdeps' in clean tree Masahiro Yamada
2019-10-03 7:58 ` [PATCH v2 5/6] nsdeps: fix hashbang of scripts/nsdeps Masahiro Yamada
2019-10-03 7:58 ` [PATCH v2 6/6] nsdeps: make generated patches independent of locale Masahiro Yamada
2019-10-07 16:43 ` [PATCH v2 0/6] module: various bug-fixes and clean-ups for module namespace Jessica Yu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191003062927.4pusu3sfjyfayigy@sruffell.net \
--to=sruffell@sruffell.net \
--cc=gregkh@linuxfoundation.org \
--cc=jeyu@kernel.org \
--cc=linux-kbuild@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maennich@google.com \
--cc=michal.lkml@markovi.net \
--cc=yamada.masahiro@socionext.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).