Commit 7d02019a07840c0263ab935f626af8002af12a91
2016-06-06T12:59:17
transports: smart: fix potential invalid memory dereferences When we receive a packet of exactly four bytes encoding its length as those four bytes it can be treated as an empty line. While it is not really specified how those empty lines should be treated, we currently ignore them and do not return an error when trying to parse it but simply advance the data pointer. Callers invoking `git_pkt_parse_line` are currently not prepared to handle this case as they do not explicitly check this case. While they could always reset the passed out-pointer to `NULL` before calling `git_pkt_parse_line` and determine if the pointer has been set afterwards, it makes more sense to update `git_pkt_parse_line` to set the out-pointer to `NULL` itself when it encounters such an empty packet. Like this it is guaranteed that there will be no invalid memory references to free'd pointers. As such, the issue has been fixed such that `git_pkt_parse_line` always sets the packet out pointer to `NULL` when an empty packet has been received and callers check for this condition, skipping such packets.
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diff --git a/src/transports/smart_pkt.c b/src/transports/smart_pkt.c
index 2ea57bb..2297cc9 100644
--- a/src/transports/smart_pkt.c
+++ b/src/transports/smart_pkt.c
@@ -433,6 +433,7 @@ int git_pkt_parse_line(
* line?
*/
if (len == PKT_LEN_SIZE) {
+ *head = NULL;
*out = line;
return 0;
}
diff --git a/src/transports/smart_protocol.c b/src/transports/smart_protocol.c
index 02e1ecf..3448fa7 100644
--- a/src/transports/smart_protocol.c
+++ b/src/transports/smart_protocol.c
@@ -759,6 +759,14 @@ static int add_push_report_sideband_pkt(git_push *push, git_pkt_data *data_pkt,
line_len -= (line_end - line);
line = line_end;
+ /* When a valid packet with no content has been
+ * read, git_pkt_parse_line does not report an
+ * error, but the pkt pointer has not been set.
+ * Handle this by skipping over empty packets.
+ */
+ if (pkt == NULL)
+ continue;
+
error = add_push_report_pkt(push, pkt);
git_pkt_free(pkt);
@@ -813,6 +821,9 @@ static int parse_report(transport_smart *transport, git_push *push)
error = 0;
+ if (pkt == NULL)
+ continue;
+
switch (pkt->type) {
case GIT_PKT_DATA:
/* This is a sideband packet which contains other packets */