When the header list is added, after the message parsing, headers with no
value are now ignored. It is not the same than headers with empty value
fields. Only headers with a NULL pointer as value are skipped. This only
happens if the header value is removed during the message
parsing. Concretly, such headers are now ignored when htx_add_all_headers()
is called. However, htx_add_header() is not affected by this change.
Symetrically, the same is true for trailers. It may be backported to 2.4
because of the previous fix ("BUG/MEDIUM: mux-h1: Remove "Upgrade:" header
for requests with payload").
Ori Hollander of JFrog Security reported that htx_add_header() and
htx_add_trailer() were missing a length check on the header name. While
this does not allow to overwrite any memory area, it results in bits of
the header name length to slip into the header value length and may
result in forging certain header names on the input. The sad thing here
is that a FIXME comment was present suggesting to add the required length
checks :-(
The injected headers are visible to the HTTP internals and to the config
rules, so haproxy will generally stay synchronized with the server. But
there is one exception which is the content-length header field, because
it is already deduplicated on the input, but before being indexed. As
such, injecting a content-length header after the deduplication stage
may be abused to present a different, shorter one on the other side and
help build a request smuggling attack, or even maybe a response splitting
attack. CVE-2021-40346 was assigned to this problem.
As a mitigation measure, it is sufficient to verify that no more than
one such header is present in any message, which is normally the case
thanks to the duplicate checks:
http-request deny if { req.hdr_cnt(content-length) gt 1 }
http-response deny if { res.hdr_cnt(content-length) gt 1 }
This must be backported to all HTX-enabled versions, hence as far as 2.0.
In 2.3 and earlier, the functions are in src/htx.c instead.
Many thanks to Ori for his work and his responsible report!
Since commit "BUG/MINOR: config: reject configs using HTTP with bufsize
>= 256 MB" we are now sure that it's not possible anymore to have an HTX
block of a size 256 MB or more, even after concatenation thanks to the
tests for len >= htx_free_data_space(). Let's remove these now obsolete
comments.
A BUG_ON() was added in htx_add_blk() to track any such exception if
the conditions would change later, to complete the one that is performed
on the start address that must remain within the buffer.
When an HTX block is expanded, a defragmentation may be performed first to
have enough space to copy the new data. When it happens, the meta data of
the HTX message must take account of the new data length but copied data are
still unchanged at this stage (because we need more space to update the
message content). And here there is a bug because the meta data are updated
by the caller. It means that when the blocks content is copied, the new
length is already set. Thus a block larger than the reality is copied and
data outside the buffer may be accessed, leading to a crash.
To fix this bug, htx_defrag() is updated to use an extra argument with the
new meta data to use for the referenced block. Thus the caller does not need
to update the HTX message by itself. However, it still have to update the
data.
Most of time, the bug will be encountered in the HTTP compression
filter. But, even if it is highly unlikely, in theory it is also possible to
hit it when a HTTP header (or only its value) is replaced or when the
start-line is changed.
This patch must be backported as far as 2.0.
The HTX functions used to add new HTX blocks in a message have been moved to
the header file to inline them in calling functions. These functions are
small enough.
The function htx_reserve_max_data() should be used to get an HTX DATA block
with the max possible size. A current block may be extended or a new one
created, depending on the HTX message state. But the idea is to let the
caller to copy a bunch of data without requesting many new blocks. It is its
responsibility to resize the block at the end, to set the final block size.
This function will be used to parse messages with small chunks. Indeed, we
can have more than 2700 1-byte chunks in a 16Kb of input data. So it is easy
to understand how this function may help to improve the parsing of chunk
messages.
The EOM block may be removed. The HTX_FL_EOM flags is enough. Most of time,
to know if the end of the message is reached, we just need to have an empty
HTX message with HTX_FL_EOM flag set. It may also be detected when the last
block of a message with HTX_FL_EOM flag is manipulated.
Removing EOM blocks simplifies the HTX message filling. Indeed, there is no
more edge problems when the message ends but there is no more space to write
the EOM block. However, some part are more tricky. Especially the
compression filter or the FCGI mux. The compression filter must finish the
compression on the last DATA block. Before it was performed on the EOM
block, an extra DATA block with the checksum was added. Now, we must detect
the last DATA block to be sure to finish the compression. The FCGI mux on
its part must be sure to reserve the space for the empty STDIN record on the
last DATA block while this record was inserted on the EOM block.
The H2 multiplexer is probably the part that benefits the most from this
change. Indeed, it is now fairly easier to known when to set the ES flag.
The HTX documentaion has been updated accordingly.
The htx_is_unique_blk() function may now be used to know if a block is the
only one in an HTX message, excluding all unused blocks. Note the purpose of
this function is not to know if a block is the last one of an HTTP message.
This means no more data part from the message are expected, except tunneled
data. It only says if a block is alone in an HTX message.
When an internal response is returned to a client, the message payload must be
skipped if it is a reply to a HEAD request. The payload is removed from the HTX
message just before the message forwarding.
This bugs has been around for a long time. It was already there in the pre-HTX
versions. In legacy HTTP mode, internal errors are not parsed. So this bug
cannot be easily fixed. Thus, this patch should only be backported in all HTX
versions, as far as 2.0. However, the code has significantly changed in the
2.2. Thus in the 2.1 and 2.0, the patch must be entirely reworked.
The HTX_FL_EOI flag must now be set on a HTX message when no more data are
expected. Most of time, it must be set before adding the EOM block. Thus, if
there is no space for the EOM, there is still an information to know all data
were received and pushed in the HTX message. There is only an exception for the
HTTP replies (deny, return...). For these messages, the flag is set after all
blocks are pushed in the message, including the EOM block, because, on error,
we remove all inserted data.
This patch fixes all the leftovers from the include cleanup campaign. There
were not that many (~400 entries in ~150 files) but it was definitely worth
doing it as it revealed a few duplicates.
Most of the file was a large set of HTX elements manipulation functions
and few types, so splitting them allowed to further reduce dependencies
and shrink the build time. Doing so revealed that a few files (h2.c,
mux_pt.c) needed haproxy/buf.h and were previously getting it through
htx.h. They were fixed.
