Messages in this thread | | | Date | Thu, 1 Apr 2021 13:53:27 -0700 | From | Eric Biggers <> | Subject | Re: [PATCH v6 4/4] fs: unicode: Add utf8 module and a unicode layer |
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On Thu, Apr 01, 2021 at 02:37:51AM +0530, Shreeya Patel wrote: > +# utf8data.h_shipped has a large database table which is an auto-generated > +# decodification trie for the unicode normalization functions and it is not > +# necessary to carry this large table in the kernel. > +# Enabling UNICODE_UTF8 option will allow UTF-8 encoding to be built as a > +# module and this module will be loaded by the unicode subsystem layer only > +# when any filesystem needs it. > +config UNICODE_UTF8 > + tristate "UTF-8 module" > help > Say Y here to enable UTF-8 NFD normalization and NFD+CF casefolding > support.
Please update this help text to properly describe this option, especially the consequences of setting it to 'm'.
> + select UNICODE
'select' should go before 'help'.
> struct unicode_map *unicode_load(const char *version) > { > + try_then_request_module(utf8mod, "utf8"); > + if (!utf8mod) { > + pr_err("Failed to load UTF-8 module\n"); > + return ERR_PTR(-ENODEV); > } > > + spin_lock(&utf8mod_lock); > + if (!utf8mod || !try_module_get(utf8mod)) { > + spin_unlock(&utf8mod_lock); > + return ERR_PTR(-ENODEV); > + } > + spin_unlock(&utf8mod_lock); > + return static_call(unicode_load_static_call)(version); > } > EXPORT_SYMBOL(unicode_load); > > void unicode_unload(struct unicode_map *um) > { > kfree(um); > + > + spin_lock(&utf8mod_lock); > + if (utf8mod) > + module_put(utf8mod); > + spin_unlock(&utf8mod_lock); > + > } > EXPORT_SYMBOL(unicode_unload); > > +void unicode_register(struct module *owner) > +{ > + utf8mod = owner; > +} > +EXPORT_SYMBOL(unicode_register); > + > +void unicode_unregister(void) > +{ > + spin_lock(&utf8mod_lock); > + utf8mod = NULL; > + spin_unlock(&utf8mod_lock); > +} > +EXPORT_SYMBOL(unicode_unregister);
This all looks very broken. First, when !CONFIG_MODULES, utf8mod will always be NULL so unicode_load() will always fail.
Also, if the unicode_load_static_call() fails, a reference to the utf8mod will be leaked.
Also, unicode_unload() can put a reference to the utf8mod that was never acquired.
Also there is a data race on utf8mod because the accesses to it aren't properly synchronized.
Please consider something like the following, which I think would address all these bugs:
static bool utf8mod_get(void) { bool ret;
spin_lock(&utf8mod_lock); ret = utf8mod_loaded && try_module_get(utf8mod); spin_unlock(&utf8mod_lock); return ret; }
struct unicode_map *unicode_load(const char *version) { struct unicode_map *um;
if (!try_then_request_module(utf8mod_get(), "utf8")) { pr_err("Failed to load UTF-8 module\n"); return ERR_PTR(-ENODEV); } um = static_call(unicode_load_static_call)(version); if (IS_ERR(um)) module_put(utf8mod); return um; } EXPORT_SYMBOL(unicode_load);
void unicode_unload(struct unicode_map *um) { if (um) { kfree(um); module_put(utf8mod); } } EXPORT_SYMBOL(unicode_unload);
void unicode_register(struct module *owner) { spin_lock(&utf8mod_lock); utf8mod = owner; /* note: will be NULL if !CONFIG_MODULES */ utf8mod_loaded = true; spin_unlock(&utf8mod_lock); } EXPORT_SYMBOL(unicode_register);
void unicode_unregister(void) { spin_lock(&utf8mod_lock); utf8mod = NULL; utf8mod_loaded = false; spin_unlock(&utf8mod_lock); } EXPORT_SYMBOL(unicode_unregister);
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