From 030e9dd64f931c0ccfb6ad4be88775f8272f02eb Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 20 Feb 2013 15:00:28 -0500 Subject: fetch-pack: fix out-of-bounds buffer offset in get_ack When we read acks from the remote, we expect either: ACK or ACK We parse the "ACK " bit from the line, and then start looking for the flag strings at "line+45"; if we don't have them, we assume it's of the first type. But if we do have the first type, then line+45 is not necessarily inside our string at all! It turns out that this works most of the time due to the way we parse the packets. They should come in with a newline, and packet_read puts an extra NUL into the buffer, so we end up with: ACK \n\0 with the newline at offset 44 and the NUL at offset 45. We then strip the newline, putting a NUL at offset 44. So when we look at "line+45", we are looking past the end of our string; but it's OK, because we hit the terminator from the original string. This breaks down, however, if the other side does not terminate their packets with a newline. In that case, our packet is one character shorter, and we start looking through uninitialized memory for the flag. No known implementation sends such a packet, so it has never come up in practice. This patch tightens the check by looking for a short, flagless ACK before trying to parse the flag. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- fetch-pack.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fetch-pack.c') diff --git a/fetch-pack.c b/fetch-pack.c index 6d8926a550..27a3e80364 100644 --- a/fetch-pack.c +++ b/fetch-pack.c @@ -226,6 +226,8 @@ static enum ack_type get_ack(int fd, unsigned char *result_sha1) return NAK; if (!prefixcmp(line, "ACK ")) { if (!get_sha1_hex(line+4, result_sha1)) { + if (len < 45) + return ACK; if (strstr(line+45, "continue")) return ACK_continue; if (strstr(line+45, "common")) -- cgit v1.2.1 From cdf4fb8e332f9641ac1ca95e999fe98251d31392 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 20 Feb 2013 15:01:56 -0500 Subject: pkt-line: drop safe_write function This is just write_or_die by another name. The one distinction is that write_or_die will treat EPIPE specially by suppressing error messages. That's fine, as we die by SIGPIPE anyway (and in the off chance that it is disabled, write_or_die will simulate it). Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- fetch-pack.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fetch-pack.c') diff --git a/fetch-pack.c b/fetch-pack.c index 27a3e80364..b53a18f923 100644 --- a/fetch-pack.c +++ b/fetch-pack.c @@ -247,7 +247,7 @@ static void send_request(struct fetch_pack_args *args, send_sideband(fd, -1, buf->buf, buf->len, LARGE_PACKET_MAX); packet_flush(fd); } else - safe_write(fd, buf->buf, buf->len); + write_or_die(fd, buf->buf, buf->len); } static void insert_one_alternate_ref(const struct ref *ref, void *unused) -- cgit v1.2.1 From 819b929d3389f6007e1c469d9060e7876caeb97f Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 20 Feb 2013 15:02:28 -0500 Subject: pkt-line: teach packet_read_line to chomp newlines The packets sent during ref negotiation are all terminated by newline; even though the code to chomp these newlines is short, we end up doing it in a lot of places. This patch teaches packet_read_line to auto-chomp the trailing newline; this lets us get rid of a lot of inline chomping code. As a result, some call-sites which are not reading line-oriented data (e.g., when reading chunks of packfiles alongside sideband) transition away from packet_read_line to the generic packet_read interface. This patch converts all of the existing callsites. Since the function signature of packet_read_line does not change (but its behavior does), there is a possibility of new callsites being introduced in later commits, silently introducing an incompatibility. However, since a later patch in this series will change the signature, such a commit would have to be merged directly into this commit, not to the tip of the series; we can therefore ignore the issue. This is an internal cleanup and should produce no change of behavior in the normal case. However, there is one corner case to note. Callers of packet_read_line have never been able to tell the difference between a flush packet ("0000") and an empty packet ("0004"), as both cause packet_read_line to return a length of 0. Readers treat them identically, even though Documentation/technical/protocol-common.txt says we must not; it also says that implementations should not send an empty pkt-line. By stripping out the newline before the result gets to the caller, we will now treat the newline-only packet ("0005\n") the same as an empty packet, which in turn gets treated like a flush packet. In practice this doesn't matter, as neither empty nor newline-only packets are part of git's protocols (at least not for the line-oriented bits, and readers who are not expecting line-oriented packets will be calling packet_read directly, anyway). But even if we do decide to care about the distinction later, it is orthogonal to this patch. The right place to tighten would be to stop treating empty packets as flush packets, and this change does not make doing so any harder. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- fetch-pack.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'fetch-pack.c') diff --git a/fetch-pack.c b/fetch-pack.c index b53a18f923..f830db224b 100644 --- a/fetch-pack.c +++ b/fetch-pack.c @@ -220,8 +220,6 @@ static enum ack_type get_ack(int fd, unsigned char *result_sha1) if (!len) die("git fetch-pack: expected ACK/NAK, got EOF"); - if (line[len-1] == '\n') - line[--len] = 0; if (!strcmp(line, "NAK")) return NAK; if (!prefixcmp(line, "ACK ")) { -- cgit v1.2.1 From 74543a0423c96130b3b07946c20b10735c3b5b15 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 20 Feb 2013 15:02:57 -0500 Subject: pkt-line: provide a LARGE_PACKET_MAX static buffer Most of the callers of packet_read_line just read into a static 1000-byte buffer (callers which handle arbitrary binary data already use LARGE_PACKET_MAX). This works fine in practice, because: 1. The only variable-sized data in these lines is a ref name, and refs tend to be a lot shorter than 1000 characters. 2. When sending ref lines, git-core always limits itself to 1000 byte packets. However, the only limit given in the protocol specification in Documentation/technical/protocol-common.txt is LARGE_PACKET_MAX; the 1000 byte limit is mentioned only in pack-protocol.txt, and then only describing what we write, not as a specific limit for readers. This patch lets us bump the 1000-byte limit to LARGE_PACKET_MAX. Even though git-core will never write a packet where this makes a difference, there are two good reasons to do this: 1. Other git implementations may have followed protocol-common.txt and used a larger maximum size. We don't bump into it in practice because it would involve very long ref names. 2. We may want to increase the 1000-byte limit one day. Since packets are transferred before any capabilities, it's difficult to do this in a backwards-compatible way. But if we bump the size of buffer the readers can handle, eventually older versions of git will be obsolete enough that we can justify bumping the writers, as well. We don't have plans to do this anytime soon, but there is no reason not to start the clock ticking now. Just bumping all of the reading bufs to LARGE_PACKET_MAX would waste memory. Instead, since most readers just read into a temporary buffer anyway, let's provide a single static buffer that all callers can use. We can further wrap this detail away by having the packet_read_line wrapper just use the buffer transparently and return a pointer to the static storage. That covers most of the cases, and the remaining ones already read into their own LARGE_PACKET_MAX buffers. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- fetch-pack.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'fetch-pack.c') diff --git a/fetch-pack.c b/fetch-pack.c index f830db224b..66ff9add89 100644 --- a/fetch-pack.c +++ b/fetch-pack.c @@ -172,8 +172,8 @@ static void consume_shallow_list(struct fetch_pack_args *args, int fd) * shallow and unshallow commands every time there * is a block of have lines exchanged. */ - char line[1000]; - while (packet_read_line(fd, line, sizeof(line))) { + char *line; + while ((line = packet_read_line(fd, NULL))) { if (!prefixcmp(line, "shallow ")) continue; if (!prefixcmp(line, "unshallow ")) @@ -215,8 +215,8 @@ static int write_shallow_commits(struct strbuf *out, int use_pack_protocol) static enum ack_type get_ack(int fd, unsigned char *result_sha1) { - static char line[1000]; - int len = packet_read_line(fd, line, sizeof(line)); + int len; + char *line = packet_read_line(fd, &len); if (!len) die("git fetch-pack: expected ACK/NAK, got EOF"); @@ -346,11 +346,11 @@ static int find_common(struct fetch_pack_args *args, state_len = req_buf.len; if (args->depth > 0) { - char line[1024]; + char *line; unsigned char sha1[20]; send_request(args, fd[1], &req_buf); - while (packet_read_line(fd[0], line, sizeof(line))) { + while ((line = packet_read_line(fd[0], NULL))) { if (!prefixcmp(line, "shallow ")) { if (get_sha1_hex(line + 8, sha1)) die("invalid shallow line: %s", line); -- cgit v1.2.1