The lack of mjson_next() prevents to iterate easily and need to hack by
iterating on a loop of snprintf + $.field[XXX] combined with
mjson_find().
This reintroduce mjson_next() so we could iterate without having to
build the string.
The patch does not reintroduce MJSON_ENABLE_NEXT so it could be used
without having to define it.
mystrtod() was not length-aware and relied on null-termination or a
non-numeric character to stop. The fix adds a length parameter as a
strict upper bound for all pointer accesses.
The practical impact in haproxy is essentially null: all callers embed
the JSON payload inside a large haproxy buffer, so the speculative read
past the last digit lands on memory that is still within the same
allocation. ASAN cannot detect it in a normal haproxy run for the same
reason — the overread never escapes the enclosing buffer. Triggering a
detectable fault requires placing the JSON payload at the exact end of
an allocation.
Note: the 'path' buffer was using a null-terminated string so the result
of strlen is passed to it, this part was not at risk.
Thanks to Kamil Frankowicz for the original bug report.
This patch must be backported to all maintained versions.
Mjson comes with its own strtod() implementation for portability
reasons and probably also because many generic strtod() versions as
provided by operating systems do not focus on resource preservation
and may call malloc(), which is not welcome in a parser.
The strtod() implementation used here apparently originally comes from
https://gist.github.com/mattn/1890186 and seems to have purposely
omitted a few parts that were considered as not needed in this context
(e.g. skipping white spaces, or setting errno). But when subject to the
relevant test cases of the designated file above, the current function
provides the same results.
The aforementioned implementation uses pow() to calculate exponents,
but mjson authors visibly preferred not to introduce a libm dependency
and replaced it with an iterative loop in O(exp) time. The problem is
that the exponent is not bounded and that this loop can take a huge
amount of time. There's even an issue already opened on mjson about
this: https://github.com/cesanta/mjson/issues/59. In the case of
haproxy, fortunately, the watchdog will quickly stop a runaway process
but this remains a possible denial of service.
A first approach would consist in reintroducing pow() like in the
original implementation, but if haproxy is built without Lua nor
51Degrees, -lm is not used so this will not work everywhere.
Anyway here we're dealing with integer exponents, so an easy alternate
approach consists in simply using shifts and squares, to compute the
exponent in O(log(exp)) time. Not only it doesn't introduce any new
dependency, but it turns out to be even faster than the generic pow()
(85k req/s per core vs 83.5k on the same machine).
This must be backported as far as 2.4, where mjson was introduced.
Many thanks to Oula Kivalo for reporting this issue.
CVE-2025-11230 was assigned to this issue.
clang 15 reports unused variables in src/mjson.c:
src/mjson.c:196:21: fatal error: expected ';' at end of declaration
int __maybe_unused n = 0;
and
src/mjson.c:727:17: fatal error: variable 'n' set but not used [-Wunused-but-set-variable]
int sign = 1, n = 0;
An issue was created on the project, but it was not fixed for now:
https://github.com/cesanta/mjson/issues/51
So for now, to fix the build issue, these variables are declared as unused.
Of course, if there is any update on this library, be careful to review this
patch first to be sure it is always required.
This patch should fix the issue #1868. It be backported as far as 2.4.
This library is required for the subsequent patch which adds
the JSON query possibility.
It is necessary to change the include statement in "src/mjson.c"
because the imported includes in haproxy are in "include/import"
orig: #include "mjson.h"
new: #include <import/mjson.h>
