From 8e932792c917d11545c2953b35159149f7411eca Mon Sep 17 00:00:00 2001 From: Alexander Monakov Date: Sun, 3 Sep 2017 22:12:20 +0300 Subject: overhaul environment functions Rewrite environment access functions to slim down code, fix bugs and avoid invoking undefined behavior. * avoid using int-typed iterators where size_t would be correct; * use strncmp instead of memcmp consistently; * tighten prologues by invoking __strchrnul; * handle NULL environ. putenv: * handle "=value" input via unsetenv too (will return -1/EINVAL); * rewrite and simplify __putenv; fix the leak caused by failure to deallocate entry added by preceding setenv when called from putenv. setenv: * move management of libc-allocated entries to this translation unit, and use no-op weak symbols in putenv/unsetenv; unsetenv: * rewrite; this fixes UB caused by testing a free'd pointer against NULL on entry to subsequent loops. Not changed: Failure to extend allocation tracking array (previously __env_map, now env_alloced) is ignored rather than causing to report -1/ENOMEM to the caller; the worst-case consequence is leaking this allocation when it is removed or replaced in a subsequent environment access. Initially UB in unsetenv was reported by Alexander Cherepanov. Using a weak alias to avoid pulling in malloc via unsetenv was suggested by Rich Felker. --- src/env/getenv.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) (limited to 'src/env/getenv.c') diff --git a/src/env/getenv.c b/src/env/getenv.c index 00c1bce0..cf34672c 100644 --- a/src/env/getenv.c +++ b/src/env/getenv.c @@ -2,13 +2,14 @@ #include #include "libc.h" +char *__strchrnul(const char *, int); + char *getenv(const char *name) { - int i; - size_t l = strlen(name); - if (!__environ || !*name || strchr(name, '=')) return NULL; - for (i=0; __environ[i] && (strncmp(name, __environ[i], l) - || __environ[i][l] != '='); i++); - if (__environ[i]) return __environ[i] + l+1; - return NULL; + size_t l = __strchrnul(name, '=') - name; + if (l && !name[l] && __environ) + for (char **e = __environ; *e; e++) + if (!strncmp(name, *e, l) && l[*e] == '=') + return *e + l+1; + return 0; } -- cgit v1.2.1