From: Alexey Spiridonov <snarkmaster@gmail.com>
Date: Mon, 2 Feb 2015 03:26:26 +0000 (-0800)
Subject: Do not request 0-length skips; sanity-check return.
X-Git-Tag: v3.1.900a~145^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=afcc3e49ad6689288245d1540ac8a1d8de27a921;p=thirdparty%2Flibarchive.git

Do not request 0-length skips; sanity-check return.

I noticed that my skip callback was always being invoked with a request of
0.  This is a bit wasteful since skip callbacks commonly involve a syscall
like lseek().

Also, it seems good to error out when the skip callback is buggy, and claims
to skip more than requested.

Test Plan:

```
autoreconf -ivf && ./configure && make && make check
```

The same tests fail as before, with the same error messages. If interested,
both failure logs are here:

https://github.com/snarkmaster/libarchive/commit/00c9751cde6cc888fb844b7a1fcc0f82dbaaedb1

These are on Ubuntu 14.04.
---

diff --git a/libarchive/archive_read.c b/libarchive/archive_read.c
index d649e9aae..2cd9726a6 100644
--- a/libarchive/archive_read.c
+++ b/libarchive/archive_read.c
@@ -195,10 +195,12 @@ client_skip_proxy(struct archive_read_filter *self, int64_t request)
 				ask = skip_limit;
 			get = (self->archive->client.skipper)
 				(&self->archive->archive, self->data, ask);
-			if (get == 0)
+			total += get;
+			if (get == 0 || get == request)
 				return (total);
+			if (get > request)
+				return ARCHIVE_FATAL;
 			request -= get;
-			total += get;
 		}
 	} else if (self->archive->client.seeker != NULL
 		&& request > 64 * 1024) {