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Date: Tue, 24 Nov 2020 06:39:59 +0300
From: Alexey Izbyshev <izbyshev@...ras.ru>
To: musl@...ts.openwall.com
Subject: Re: realpath without procfs -- should be ready for inclusion
On 2020-11-23 23:53, Rich Felker wrote:
> On Mon, Nov 23, 2020 at 01:56:33PM -0500, Rich Felker wrote:
>> On Sun, Nov 22, 2020 at 10:19:33PM -0500, Rich Felker wrote:
>> --- realpath8.c 2020-11-22 17:52:17.586481571 -0500
>> +++ realpath9.c 2020-11-23 13:55:06.808458893 -0500
>> @@ -19,7 +19,7 @@
>> char *output = resolved ? resolved : buf;
>> size_t p, q, l, cnt=0;
>>
>> - l = strnlen(filename, sizeof stack + 1);
>> + l = strnlen(filename, sizeof stack);
>> if (!l) {
>> errno = ENOENT;
>> return 0;
>> @@ -80,11 +80,16 @@
>> return 0;
>> }
>> if (k==p) goto toolong;
>> + if (!k) {
>> + errno = ENOENT;
>> + return 0;
>> + }
>> if (++cnt == SYMLOOP_MAX) {
>> errno = ELOOP;
>> return 0;
>> }
>> p -= k;
>> + if (stack[k-1]=='/') p++;
>> memmove(stack+p, stack, k);
>
> This is wrong and needs further consideration.
>
Yes, now memmove() overwrites NUL if p was at the end and stack[k-1] ==
'/'. Is it true per POSIX that "rr/home" must resolve to "//home" if
"rr" -> "//"? If so, maybe something like the following instead:
+ while (stack[p] == '/') p++;
+ if (stack[p] && stack[k-1] != '/') p--;
p -= k;
- if (stack[k-1]=='/') p++;
>> }
>>
>> @@ -95,7 +100,8 @@
>> l = strlen(stack);
>> /* Cancel any initial .. components. */
>> p = 0;
>> - while (q-p>=2 && at_dotdot(output+p+2, p+2)) {
>> + while (output[p]=='.' && output[p+1]=='.'
>> + && (!output[p+2] || output[p+2]=='/')) {
>> while(l>1 && stack[l-1]!='/') l--;
>> if (l>1) l--;
>> p += 2;
>
> OK, I have a better improvement for this: counting the number of
> levels of .. as they're built at the head of output. Then it's just
> while (nup--) here, and the condition for canceling .. in the first
> loop no longer needs any string inspection; it's just (q>3*nup).
>
Sounds good.
I've missed the last time that the immediately following code is also
broken:
> if (q-p && stack[l-1]!='/') output[--p] = '/';
It will underflow the output in case of a simple relative path that
doesn't start with "..".
I've also noticed other issues to be fixed, per POSIX:
* ENOENT should be returned if filename is NULL
* ENOTDIR should be returned if the last component is not a directory
and the path has one or more trailing slashes
Alexey
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