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authorMichal Nazarewicz <mina86@mina86.com>2013-11-12 15:08:41 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-11-13 12:09:12 +0900
commitc725ee54c30b34427cb8fa68d1fe8804aca6d400 (patch)
treeb455af08fbecb6a3f7ddf027cbc4b36d3865bf9e /usr
parent0ca43435188b9f911c8efcdf10731f726142dda1 (diff)
gen_init_cpio: avoid NULL pointer dereference and rework env expanding
getenv() may return NULL if given environment variable does not exist which leads to NULL dereference when calling strncat. Besides that, the environment variable name was copied to a temporary env_var buffer, but this copying can be avoided by simply using the input string. Lastly, the whole loop can be greatly simplified by using the snprintf function instead of the playing with strncat. By the way, the current implementation allows a recursive variable expansion, as in: $ echo 'out ${A} out ' | A='a ${B} a' B=b /tmp/a out a b a out I'm assuming this is just a side effect and not a conscious decision (especially as this may lead to infinite loop), but I didn't want to change this behaviour without consulting. If the current behaviour is deamed incorrect, I'll be happy to send a patch without recursive processing. Signed-off-by: Michal Nazarewicz <mina86@mina86.com> Cc: Kees Cook <keescook@chromium.org> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Jesper Juhl <jj@codesealer.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'usr')
-rw-r--r--usr/gen_init_cpio.c27
1 files changed, 9 insertions, 18 deletions
diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
index af8c925e93eb..225ad244cf88 100644
--- a/usr/gen_init_cpio.c
+++ b/usr/gen_init_cpio.c
@@ -382,24 +382,15 @@ error:
static char *cpio_replace_env(char *new_location)
{
char expanded[PATH_MAX + 1];
- char env_var[PATH_MAX + 1];
- char *start;
- char *end;
-
- for (start = NULL; (start = strstr(new_location, "${")); ) {
- end = strchr(start, '}');
- if (start < end) {
- *env_var = *expanded = '\0';
- strncat(env_var, start + 2, end - start - 2);
- strncat(expanded, new_location, start - new_location);
- strncat(expanded, getenv(env_var),
- PATH_MAX - strlen(expanded));
- strncat(expanded, end + 1,
- PATH_MAX - strlen(expanded));
- strncpy(new_location, expanded, PATH_MAX);
- new_location[PATH_MAX] = 0;
- } else
- break;
+ char *start, *end, *var;
+
+ while ((start = strstr(new_location, "${")) &&
+ (end = strchr(start + 2, '}'))) {
+ *start = *end = 0;
+ var = getenv(start + 2);
+ snprintf(expanded, sizeof expanded, "%s%s%s",
+ new_location, var ? var : "", end + 1);
+ strcpy(new_location, expanded);
}
return new_location;

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