| Message ID | 20191003075826.7478-3-yamada.masahiro@socionext.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | module: various bug-fixes and clean-ups for module namespace | expand |
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>
Hi Shaun, On Thu, Oct 3, 2019 at 10:29 PM Shaun Ruffell <sruffell@sruffell.net> wrote: > > 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) You have a point. The change to check_exports() looks strange. It is actually related to my previous patch submission. See this patch: https://lore.kernel.org/patchwork/patch/1131970/ Currently, the NULL pointer means no namespace. I noticed passing an empty string as the namespace simplified <linux/export.h> a lot. So, I changed it in a way that an empty string also means no namespace. Anyway, Matthias took over the refactoring work. So, I am not sure if this change is still helpful... If it is no longer useful, I am happy to send v3 with the following: diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 442d5e2ad688..bdd3956e89c9 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -2453,6 +2453,8 @@ static void read_dump(const char *fname, unsigned int kernel) mod = new_module(modname); mod->skip = 1; } + if (namespace[0] == '\0') + namespace = NULL; s = sym_add_exported(symname, namespace, mod, export_no(export)); s->kernel = kernel;
+++ Masahiro Yamada [03/10/19 23:42 +0900]: >Hi Shaun, > >On Thu, Oct 3, 2019 at 10:29 PM Shaun Ruffell <sruffell@sruffell.net> wrote: >> >> 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) > >You have a point. > >The change to check_exports() looks strange. >It is actually related to my previous patch submission. > >See this patch: >https://lore.kernel.org/patchwork/patch/1131970/ > > >Currently, the NULL pointer means no namespace. > >I noticed passing an empty string as the namespace >simplified <linux/export.h> a lot. > >So, I changed it in a way that >an empty string also means no namespace. > > >Anyway, Matthias took over the refactoring work. >So, I am not sure if this change is still helpful... Hm, I agree that the inconsistency (empty string vs. NULL) is a bit confusing. I do not mind too much either way - but if we allow both NULL and the empty string to represent "no namespace", perhaps we should at least document this in a comment next to the namespace field in struct symbol and also next to the check in check_exports() so that it's clear that both can mean no namespace. >If it is no longer useful, I am happy to send v3 >with the following: > > >diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c >index 442d5e2ad688..bdd3956e89c9 100644 >--- a/scripts/mod/modpost.c >+++ b/scripts/mod/modpost.c >@@ -2453,6 +2453,8 @@ static void read_dump(const char *fname, >unsigned int kernel) > mod = new_module(modname); > mod->skip = 1; > } >+ if (namespace[0] == '\0') >+ namespace = NULL; > s = sym_add_exported(symname, namespace, mod, > export_no(export)); > s->kernel = kernel; >
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);