segfault bb_make_directory + dirname with musl
Tito
farmatito at tiscali.it
Tue Dec 6 21:32:04 UTC 2016
On 11/30/2016 11:52 PM, Denys Vlasenko wrote:
> On Wed, Nov 30, 2016 at 3:46 AM, Daniel Sabogal <dsabogalcc at gmail.com> wrote:
>> The following commands cause busybox to segfault on musl-based systems.
>>
>> $ install -D a /
>> $ install -D a /b
>> $ install -D a /b/
>>
>> This happens because the code in
>>
>> https://git.busybox.net/busybox/tree/coreutils/install.c?h=1_25_1#n196
>>
>> passes the result of dirname() to bb_make_directory() which modifies its
>> contents. For paths of the above forms, musl's dirname returns a string
>> literal "/" which shouldn't be modified.
>>
>> See http://git.musl-libc.org/cgit/musl/tree/src/misc/dirname.c
>>
>> There are a few other occurrences of the code shown above, but I've not
>> checked to see if they could be made to segfault.
>
> Does this fix the problem?
>
> /* Bypass leading non-'/'s and then subsequent '/'s */
> while (*s) {
> if (*s == '/') {
> do {
> ++s;
> } while (*s == '/');
> c = *s; /* Save the current char */
> ====added line==> if (c)
> *s = '\0'; /* and
> replace it with nul */
> break;
> _______________________________________________
Hi,
don't know if this could be useful, but reading this thread inspired
me to write dirname and basename replacement functions for busybox
that return a malloced string that could be modified by the caller.
The functions seem to work nice as standalone program and both
pass the tests as in the man 3 basename examples and a few more
added by me.
/* Man 3 BASENAME examples (taken from SUSv2)
path dirname basename
/usr/lib /usr lib
/usr/ / usr
usr . usr
/ / /
. . .
.. . ..
Added examples:
usr/lib usr lib
usr/lib/ usr lib
usr/ . usr
/usr . usr
/a/b/c /a/b c
/a/b/c/ /a/b c
a/b/c a/b c
a/b/c/ a/b c
// / /
/// / /
//// / /
'/a/b/ ' /a/b ' '
*/
The functions look like this:
char* bb_basename_malloc(const char *name)
{
const char *p1 = NULL;
const char *p2 = NULL;
const char *s = name;
char *last = last_char_is(s, '/');
while (*s) {
if (*s == '/') {
p2 = p1;
p1 = s;
}
s++;
}
if (last) {
if(p2)
name = p2 + 1;
} else if (p1) {
name = p1 + 1;
}
return xstrndup(name, strlen(name) - (last && last != name));
}
char* bb_dirname_malloc(const char *name)
{
int len = 0;
const char *p1 = NULL;
const char *p2 = NULL;
const char *s = name;
while (*s) {
if (*s == '/' && ((s[1] && s[1] != '/') || s == name)) {
p2 = p1;
p1 = s;
}
s++;
}
if (!p2 && !p1)
return xstrdup(".");
if (p1 == name && !p2)
return xstrdup("/");
if (p1)
len = strlen(p1);
return xstrndup(name, strlen(name) - len);
}
Attached you will find the standalone version to test the functions.
Hints, critics, improvements are welcome.
Ciao,
Tito
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