From a769390da604b4815535e296d8a46fdf9094c2c7 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Mon, 3 Oct 2016 15:01:06 +0200 Subject: [PATCH] hush: fix a memory corruption when exported variable is modified The construct such as this: t=1 export t t=new_value1 had a small probability of momentarily using free()d value. Signed-off-by: Denys Vlasenko --- shell/hush.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) diff --git a/shell/hush.c b/shell/hush.c index d0d983018..668b1f2b7 100644 --- a/shell/hush.c +++ b/shell/hush.c @@ -1891,6 +1891,7 @@ static int set_local_var(char *str, int flg_export, int local_lvl, int flg_read_ { struct variable **var_pp; struct variable *cur; + char *free_me = NULL; char *eq_sign; int name_len; @@ -1907,6 +1908,7 @@ static int set_local_var(char *str, int flg_export, int local_lvl, int flg_read_ var_pp = &cur->next; continue; } + /* We found an existing var with this name */ if (cur->flg_read_only) { #if !BB_MMU @@ -1955,12 +1957,17 @@ static int set_local_var(char *str, int flg_export, int local_lvl, int flg_read_ strcpy(cur->varstr, str); goto free_and_exp; } - } else { - /* max_len == 0 signifies "malloced" var, which we can - * (and has to) free */ - free(cur->varstr); - } - cur->max_len = 0; + /* Can't reuse */ + cur->max_len = 0; + goto set_str_and_exp; + } + /* max_len == 0 signifies "malloced" var, which we can + * (and have to) free. But we can't free(cur->varstr) here: + * if cur->flg_export is 1, it is in the environment. + * We should either unsetenv+free, or wait until putenv, + * then putenv(new)+free(old). + */ + free_me = cur->varstr; goto set_str_and_exp; } @@ -1987,10 +1994,15 @@ static int set_local_var(char *str, int flg_export, int local_lvl, int flg_read_ cur->flg_export = 0; /* unsetenv was already done */ } else { + int i; debug_printf_env("%s: putenv '%s'\n", __func__, cur->varstr); - return putenv(cur->varstr); + i = putenv(cur->varstr); + /* only now we can free old exported malloced string */ + free(free_me); + return i; } } + free(free_me); return 0; } -- 2.25.1