[UNIX] Squid's ICAP Implementation Lacks Defer Check When Reading From ICAP Server

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Squid's ICAP Implementation Lacks Defer Check When Reading From ICAP
Server
------------------------------------------------------------------------

SUMMARY

A vulnerability in Squid's ICAP implementation allows attackers to cause
Squid to consume large amounts of memory.

DETAILS

Vulnerable Systems:
* Squid version 2.5
* Squid version 2.6

Squid's ICAP implementation does not check mem-store size before reading
from an ICAP-server. If the user does not confirm browsers
download-message-box, Squid keeps on reading data from the ICAP server
into the memory store, whilst no more data can be delivered to the client.
Thus the memory store is growing and Squid may - in worst case - consume
memory up to the size of the users download.

Patch:
diff -Naur squid-2.5.STABLE10.ICAP.orig/src/icap_respmod.c
squid-2.5.STABLE10.ICAP/src/icap_respmod.c
--- squid-2.5.STABLE10.ICAP.orig/src/icap_respmod.c 2007-12-07
08:48:14.124859537 +0100
+++ squid-2.5.STABLE10.ICAP/src/icap_respmod.c 2007-12-07
08:49:23.501573696 +0100
@@ -49,6 +49,7 @@
static int icapReadReply2(IcapStateData * icap);
static void icapReadReply3(IcapStateData * icap);
static void write_av_stat(char *virus, char *statsrc, char *statdst);
+static int icapCheckDeferRead(int fd, void *data);

#define EXPECTED_ICAP_HEADER_LEN 256
const char *crlf = "\r\n";
@@ -415,7 +416,7 @@
ErrorState *err;
const char *start;
const char *end;
-
+
debug(81, 5) ("icapRespModReadReply: FD %d data = %p\n", fd, data);
statCounter.syscalls.sock.reads++;

@@ -1100,6 +1102,7 @@
} else if (!icap->flags.no_content) {
/* Wait for EOF condition */
commSetSelect(fd, COMM_SELECT_READ, icapReadReply, icap, 0);
+ commSetDefer(fd, icapCheckDeferRead, icap);
debug(81,
3)
("icapReadReply3: Going to read mode data throught
icapReadReply\n");
@@ -1134,3 +1137,27 @@
strcat(subsrvProto, statsrc);
send_service_stat(rid, 10, avServer, avService, subsrvProto, virus,
statdst, 0, 1, featured);
}
+
+static int
+icapCheckDeferRead(int fd, void *data)
+{
+ IcapStateData *httpState = data;
+ StoreEntry *e = httpState->respmod.entry;
+ MemObject *mem = e->mem_obj;
+
+ int rc=0;
+
+ if (EBIT_TEST(e->flags, ENTRY_FWD_HDR_WAIT))
+ return rc;
+ if (EBIT_TEST(e->flags, RELEASE_REQUEST)) {
+ if (mem->inmem_hi - mem->inmem_lo > SM_PAGE_SIZE +
Config.Store.maxInMemObjSize + READ_AHEAD_GAP){
+ debug(81, 5) ("icapCheckDeferRead: Defering read\n");
+ return 1;
+ }
+ }
+ if (mem->inmem_hi - storeLowestMemReaderOffset(e) > READ_AHEAD_GAP){
+ debug(81, 5) ("icapCheckDeferRead: Defering read\n");
+ return 1;
+ }
+ return 0;
+}

ADDITIONAL INFORMATION

The information has been provided by <mailto:m.huter@phion.com> Martin
Huter.
The original article can be found at:
<http://www.squid-cache.org/bugs/show_bug.cgi?id=2136>

http://www.squid-cache.org/bugs/show_bug.cgi?id=2136

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