File systemtap-CVE-unwind-table-size-checks.patch of Package systemtap

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File systemtap-CVE-unwind-table-size-checks.patch of Package systemtap (Revision 40f4f2d646ae9ba15ec9a17ed78b01ea)

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From: Jan Lieskovsky <jlieskov@redhat.com>
Subject: Three SystemTap-1.0 denial of service issues
References: CVE-2009-2911, BNC#548361
Upstream: yes

Three denial of service flaws were found in the SystemTap
instrumentation system of version 1.0, when the --unprivileged mode was
activated:

c, Absent check(s) for the upper bound of the size of the unwind table
   and for the upper bound of the size of each of the CIE/CFI records, could
   allow an attacker to cause a denial of service (infinite loop).

diff --git a/runtime/unwind.c b/runtime/unwind.c
index 00108a3..7607770 100644
--- a/runtime/unwind.c
+++ b/runtime/unwind.c
@@ -88,7 +88,7 @@ static sleb128_t get_sleb128(const u8 **pcur, const u8 *end)
 
 /* given an FDE, find its CIE */
 static const u32 *cie_for_fde(const u32 *fde, void *unwind_data,
-			      int is_ehframe)
+			      uint32_t table_len, int is_ehframe)
 {
 	const u32 *cie;
 
@@ -118,6 +118,11 @@ static const u32 *cie_for_fde(const u32 *fde, void *unwind_data,
 	else
 		cie = unwind_data + fde[1];
 
+	/* Make sure address falls in the table */
+	if (((void *)cie) < ((void*)unwind_data)
+	    || ((void*)cie) > ((void*)(unwind_data + table_len)))
+	  return NULL;
+
 	if (*cie <= sizeof(*cie) + 4 || *cie >= fde[1] - sizeof(*fde)
 	    || (*cie & (sizeof(*cie) - 1))
 	    || (cie[1] != 0xffffffff && cie[1] != 0)) {
@@ -200,7 +205,8 @@ static unsigned long read_pointer(const u8 **pLoc, const void *end, signed ptrTy
 	return value;
 }
 
-static signed fde_pointer_type(const u32 *cie)
+static signed fde_pointer_type(const u32 *cie, void *unwind_data,
+			       uint32_t table_len)
 {
 	const u8 *ptr = (const u8 *)(cie + 2);
 	unsigned version = *ptr;
@@ -212,11 +218,16 @@ static signed fde_pointer_type(const u32 *cie)
 		const u8 *end = (const u8 *)(cie + 1) + *cie;
 		uleb128_t len;
 
+		/* end of cie should fall within unwind table. */
+		if (((void*)end) < ((void *)unwind_data)
+		    || ((void *)end) > ((void *)(unwind_data + table_len)))
+		  return -1;
+
 		/* check if augmentation size is first (and thus present) */
 		if (*ptr != 'z')
 			return -1;
 		/* check if augmentation string is nul-terminated */
-		if ((ptr = memchr(aug = (const void *)ptr, 0, end - ptr)) == NULL)
+		if ((ptr = memchr(aug = (const void *)ptr, 0, end - ptr)) == NULL) 
 			return -1;
 		++ptr;		/* skip terminator */
 		get_uleb128(&ptr, end);	/* skip code alignment */
@@ -267,6 +278,10 @@ static void set_rule(uleb128_t reg, enum item_location where, uleb128_t value, s
 	}
 }
 
+/* Limit the number of instructions we process. Arbitrary limit.
+   512 should be enough for anybody... */
+#define MAX_CFI 512
+
 static int processCFI(const u8 *start, const u8 *end, unsigned long targetLoc, signed ptrType, struct unwind_state *state)
 {
 	union {
@@ -276,6 +291,9 @@ static int processCFI(const u8 *start, const u8 *end, unsigned long targetLoc, s
 	} ptr;
 	int result = 1;
 
+	if (end - start > MAX_CFI)
+	  return 0;
+
 	dbug_unwind(1, "targetLoc=%lx state->loc=%lx\n", targetLoc, state->loc);
 	if (start != state->cieStart) {
 		state->loc = state->org;
@@ -606,10 +624,10 @@ static int unwind_frame(struct unwind_frame_info *frame,
 
 	/* found the fde, now set startLoc and endLoc */
 	if (fde != NULL) {
-		cie = cie_for_fde(fde, table, is_ehframe);
+		cie = cie_for_fde(fde, table, table_len, is_ehframe);
 		if (likely(cie != NULL && cie != &bad_cie && cie != &not_fde)) {
 			ptr = (const u8 *)(fde + 2);
-			ptrType = fde_pointer_type(cie);
+			ptrType = fde_pointer_type(cie, table, table_len);
 			startLoc = read_pointer(&ptr, (const u8 *)(fde + 1) + *fde, ptrType);
 			startLoc = adjustStartLoc(startLoc, m, s, ptrType, is_ehframe);
 
@@ -632,12 +650,12 @@ static int unwind_frame(struct unwind_frame_info *frame,
 	    for (fde = table, tableSize = table_len; cie = NULL, tableSize > sizeof(*fde)
 		 && tableSize - sizeof(*fde) >= *fde; tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
 			dbug_unwind(3, "fde=%lx tableSize=%d\n", (long)*fde, (int)tableSize);
-			cie = cie_for_fde(fde, table, is_ehframe);
+			cie = cie_for_fde(fde, table, table_len, is_ehframe);
 			if (cie == &bad_cie) {
 				cie = NULL;
 				break;
 			}
-			if (cie == NULL || cie == &not_fde || (ptrType = fde_pointer_type(cie)) < 0)
+			if (cie == NULL || cie == &not_fde || (ptrType = fde_pointer_type(cie, table, table_len)) < 0)
 				continue;
 
 			ptr = (const u8 *)(fde + 2);
@@ -666,6 +684,12 @@ static int unwind_frame(struct unwind_frame_info *frame,
 	state.cieEnd = ptr;	/* keep here temporarily */
 	ptr = (const u8 *)(cie + 2);
 	end = (const u8 *)(cie + 1) + *cie;
+
+	/* end should fall within unwind table. */
+	if (((void *)end) < table
+	    || ((void *)end) > ((void *)(table + table_len)))
+	  goto err;
+
 	frame->call_frame = 1;
 	if ((state.version = *ptr) != 1) {
 		dbug_unwind(1, "CIE version number is %d.  1 is supported.\n", state.version);
@@ -723,6 +747,11 @@ static int unwind_frame(struct unwind_frame_info *frame,
 	state.cieEnd = end;
 	end = (const u8 *)(fde + 1) + *fde;
 
+	/* end should fall within unwind table. */
+	if (((void*)end) < table
+	    || ((void *)end) > ((void *)(table + table_len)))
+	  goto err;
+
 	/* skip augmentation */
 	if (((const char *)(cie + 2))[1] == 'z') {
 		uleb128_t augSize = get_uleb128(&ptr, end);
diff --git a/runtime/unwind/unwind.h b/runtime/unwind/unwind.h
index 285a3a3..023ea60 100644
--- a/runtime/unwind/unwind.h
+++ b/runtime/unwind/unwind.h
@@ -143,8 +143,10 @@ static unsigned long read_pointer(const u8 **pLoc,
                                   const void *end,
                                   signed ptrType);
 static const u32 bad_cie, not_fde;
-static const u32 *cie_for_fde(const u32 *fde, void *table, int is_ehframe);
-static signed fde_pointer_type(const u32 *cie);
+static const u32 *cie_for_fde(const u32 *fde, void *table,
+			      uint32_t table_len, int is_ehframe);
+static signed fde_pointer_type(const u32 *cie,
+			       void *table, uint32_t table_len);
 
 
 #endif /* STP_USE_DWARF_UNWINDER */
diff --git a/translate.cxx b/translate.cxx
index bc5d615..9d456bc 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -29,6 +29,11 @@ extern "C" {
 #include <elfutils/libdwfl.h>
 }
 
+// Max unwind table size (debug or eh) per module. Somewhat arbitrary
+// limit (a bit more than twice the .debug_frame size of my local
+// vmlinux for 2.6.31.4-83.fc12.x86_64)
+#define MAX_UNWIND_TABLE_SIZE (3 * 1024 * 1024)
+
 using namespace std;
 
 struct var;
@@ -4785,6 +4790,9 @@ dump_unwindsyms (Dwfl_Module *m,
   get_unwind_data (m, &debug_frame, &eh_frame, &debug_len, &eh_len, &eh_addr);
   if (debug_frame != NULL && debug_len > 0)
     {
+      if (debug_len > MAX_UNWIND_TABLE_SIZE)
+	throw semantic_error ("module debug unwind table size too big");
+
       c->output << "#if defined(STP_USE_DWARF_UNWINDER) && defined(STP_NEED_UNWIND_DATA)\n";
       c->output << "static uint8_t _stp_module_" << stpmod_idx
 		<< "_debug_frame[] = \n";
@@ -4802,6 +4810,9 @@ dump_unwindsyms (Dwfl_Module *m,
 
   if (eh_frame != NULL && eh_len > 0)
     {
+      if (eh_len > MAX_UNWIND_TABLE_SIZE)
+	throw semantic_error ("module eh unwind table size too big");
+
       c->output << "#if defined(STP_USE_DWARF_UNWINDER) && defined(STP_NEED_UNWIND_DATA)\n";
       c->output << "static uint8_t _stp_module_" << stpmod_idx
 		<< "_eh_frame[] = \n";

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File systemtap-CVE-unwind-table-size-checks.patch of Package systemtap (Revision 40f4f2d646ae9ba15ec9a17ed78b01ea)

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