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modpost: fix broken sym->namespace for external module builds 

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.

Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
This commit is contained in:
Masahiro Yamada 2019-10-03 16:58:22 +09:00 committed by Jessica Yu
parent bf70b0503a
commit 389eb3f5f4
1 changed files with 8 additions and 5 deletions
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13
scripts/mod/modpost.c
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@ -166,7 +166,7 @@ struct symbol {
struct module *module; struct module *module;
unsigned int crc; unsigned int crc;
int crc_valid; int crc_valid;
const char *namespace; char *namespace;
unsigned int weak:1; unsigned int weak:1;
unsigned int vmlinux:1; /* 1 if symbol is defined in vmlinux */ unsigned int vmlinux:1; /* 1 if symbol is defined in vmlinux */
unsigned int kernel:1; /* 1 if symbol is from kernel 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; return export_unknown;
} }
static const char *sym_extract_namespace(const char **symname) static char *sym_extract_namespace(const char **symname)
{ {
char *namespace = NULL; char *namespace = NULL;
char *ns_separator; char *ns_separator;
@ -373,7 +373,6 @@ static struct symbol *sym_add_exported(const char *name, const char *namespace,
if (!s) { if (!s) {
s = new_symbol(name, mod, export); s = new_symbol(name, mod, export);
s->namespace = namespace;
} else { } else {
if (!s->preloaded) { if (!s->preloaded) {
warn("%s: '%s' exported twice. Previous export was in %s%s\n", 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; s->module = mod;
} }
} }
free(s->namespace);
s->namespace = namespace ? strdup(namespace) : NULL;
s->preloaded = 0; s->preloaded = 0;
s->vmlinux = is_vmlinux(mod->name); s->vmlinux = is_vmlinux(mod->name);
s->kernel = 0; s->kernel = 0;
@ -670,7 +671,8 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
unsigned int crc; unsigned int crc;
enum export export; enum export export;
bool is_crc = false; bool is_crc = false;
const char *name, *namespace; const char *name;
char *namespace;
if ((!is_vmlinux(mod->name) || mod->is_dot_o) && if ((!is_vmlinux(mod->name) || mod->is_dot_o) &&
strstarts(symname, "__ksymtab")) strstarts(symname, "__ksymtab"))
@ -745,6 +747,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
name = symname + strlen("__ksymtab_"); name = symname + strlen("__ksymtab_");
namespace = sym_extract_namespace(&name); namespace = sym_extract_namespace(&name);
sym_add_exported(name, namespace, mod, export); sym_add_exported(name, namespace, mod, export);
free(namespace);
} }
if (strcmp(symname, "init_module") == 0) if (strcmp(symname, "init_module") == 0)
mod->has_init = 1; mod->has_init = 1;
@ -2193,7 +2196,7 @@ static int check_exports(struct module *mod)
else else
basename = mod->name; basename = mod->name;
if (exp->namespace) { if (exp->namespace && exp->namespace[0]) {
add_namespace(&mod->required_namespaces, add_namespace(&mod->required_namespaces,
exp->namespace); exp->namespace);