From: Eugene Syromyatnikov <evgsyr@gmail.com>
Date: Wed, 23 May 2018 16:50:48 +0000 (+0200)
Subject: nlattr: add size check to decode_nla_xval and decode_nla_flags
X-Git-Tag: v4.23~42
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=c0827b1ae93fa892a3e9cd97940d2b846b97b1b5;p=strace

nlattr: add size check to decode_nla_xval and decode_nla_flags

If the field size is known, do not print as valid numbers those
attributes that are too short, and ignore extra data.

This change puts xval/flags printing in line with the reset of attribute
decoders.

* nlattr.h (struct decode_nla_xlat_opts): Add size field.
* nlattr.c (decode_nla_xval, decode_nla_flags): Check that len is at
least opts->size, limit len to opts->size.
(decode_nla_ip_proto): Specify size of 1.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>
---

diff --git a/nlattr.c b/nlattr.c
index 3484c03b..cee827fc 100644
--- a/nlattr.c
+++ b/nlattr.c
@@ -283,22 +283,24 @@ decode_nla_ifindex(struct tcb *const tcp,
 bool
 decode_nla_xval(struct tcb *const tcp,
 		const kernel_ulong_t addr,
-		const unsigned int len,
+		unsigned int len,
 		const void *const opaque_data)
 {
 	const struct decode_nla_xlat_opts * const opts = opaque_data;
 	union {
 		uint64_t val;
 		uint8_t  bytes[sizeof(uint64_t)];
-	} data;
-	const size_t bytes_offs = is_bigendian ? sizeof(data) - len : 0;
-
-	data.val = 0;
+	} data = { .val = 0 };
 
-	if (len > sizeof(data))
+	if (len > sizeof(data) || len < opts->size)
 		return false;
-	else if (!umoven_or_printaddr(tcp, addr, len, data.bytes + bytes_offs))
-	{
+
+	if (opts->size)
+		len = MIN(len, opts->size);
+
+	const size_t bytes_offs = is_bigendian ? sizeof(data) - len : 0;
+
+	if (!umoven_or_printaddr(tcp, addr, len, data.bytes + bytes_offs)) {
 		if (opts->process_fn)
 			data.val = opts->process_fn(data.val);
 		if (opts->prefix)
@@ -348,6 +350,7 @@ decode_nla_ip_proto(struct tcb *const tcp,
 		.xlat_size = inet_protocols_size,
 		.xt = XT_SORTED,
 		.dflt = "IPPROTO_???",
+		.size = 1,
 	};
 
 	return decode_nla_xval(tcp, addr, len, &opts);
@@ -356,7 +359,7 @@ decode_nla_ip_proto(struct tcb *const tcp,
 bool
 decode_nla_flags(struct tcb *const tcp,
 		 const kernel_ulong_t addr,
-		 const unsigned int len,
+		 unsigned int len,
 		 const void *const opaque_data)
 {
 	const struct decode_nla_xlat_opts * const opts = opaque_data;
@@ -364,16 +367,20 @@ decode_nla_flags(struct tcb *const tcp,
 		uint64_t flags;
 		uint8_t  bytes[sizeof(uint64_t)];
 	} data = { .flags = 0 };
+
+	if (len > sizeof(data) || len < opts->size)
+		return false;
+
+	if (opts->size)
+		len = MIN(len, opts->size);
+
 	const size_t bytes_offs = is_bigendian ? sizeof(data) - len : 0;
 
 	if (opts->xt == XT_INDEXED)
 		error_func_msg("indexed xlats are currently incompatible with "
 			       "printflags");
 
-	if (len > sizeof(data))
-		return false;
-	else if (!umoven_or_printaddr(tcp, addr, len, data.bytes + bytes_offs))
-	{
+	if (!umoven_or_printaddr(tcp, addr, len, data.bytes + bytes_offs)) {
 		if (opts->process_fn)
 			data.flags = opts->process_fn(data.flags);
 		if (opts->prefix)
diff --git a/nlattr.h b/nlattr.h
index 10e085c4..34a36ad0 100644
--- a/nlattr.h
+++ b/nlattr.h
@@ -41,6 +41,7 @@ struct decode_nla_xlat_opts {
 	const char *prefix;
 	const char *suffix;
 	uint64_t (*process_fn)(uint64_t val);
+	size_t size;
 };
 
 typedef bool (*nla_decoder_t)(struct tcb *, kernel_ulong_t addr,