path: root/src/env/getenv.c
diff options
authorAlexander Monakov <>2017-09-03 22:12:20 +0300
committerRich Felker <>2017-09-04 15:55:05 -0400
commit8e932792c917d11545c2953b35159149f7411eca (patch)
tree330b20d848bf624c9b7a00c1c0ae0181e3b85e93 /src/env/getenv.c
parent39db00afadc9d8d0456c46eab42b8cb8ff9f375c (diff)
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.
Diffstat (limited to 'src/env/getenv.c')
1 files changed, 8 insertions, 7 deletions
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 <string.h>
#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;