In a file called huff-tables.h in ls-qpack, some calculations where happening based on the following code: #if __BYTE_ORDER == __LITTLE_ENDIAN #define I(i,j) ((j<<8)|i) #else #define I(i,j) ((i<<8)|j) #endif Surprisingly when compiled with the c99 standards the #else part was getting executed while for gnu99 #if part was getting triggered. Writing some #ifdef statements it was found that __BYTE_ORDER and __LITTLE_ENDIAN were not defined when compiled with c99 and hence the macro evaluated to #if NULL == NULL which caused the little endian logic of the code to get executed. In little endian systems, this would not be an issue as either ways only little endian part of the logic will get executed. __BYTE_ORDER and __LITTLE_ENDIAN are defined in the header file endian.h in glibc. This header file is automatically included when compiling with gnu99 and not when compiling with c99(This was tested by preprocessing with both c99 and gnu99 with the -E flag passed to gcc). In the setup.py file of pylsqpack it is mentioned to adhere to c99 standards. So, adding <endian.h> header file to lsqpack.c file seems to fix the issue. Please see if the attached patch is fine. I also am not aware of how to submit a patch. So, if the attached patch is all good, can you please guide me on how to submit the patch.
Also, thanks Colin for the patch. I tested that out. But it failed with -std=gnu99 and hence I ran the ls-qpack's test cases, and it failed there as well (Because ls-qpack is compiling without passing any -std flags which defaults to gnu standards). Thank you ________________________________ From: Colin Watson <cjwat...@debian.org> Sent: Tuesday, March 18, 2025 12:11 AM To: Pranav P <pranav...@ibm.com>; 1099...@bugs.debian.org <1099...@bugs.debian.org> Cc: Paul Gevers <elb...@debian.org>; debian-s...@lists.debian.org <debian-s...@lists.debian.org> Subject: [EXTERNAL] Re: Bug#1099935: dnspython: autopkgtest regression on s390x: bad request Control: reassign -1 python3-pylsqpack 0.3.18-1 Control: affects -1 src:dnspython On Mon, Mar 17, 2025 at 05:03:56PM +0000, Colin Watson wrote: >On Sun, Mar 16, 2025 at 12:12:08PM +0000, Pranav P wrote: >>I am still continuing my search on the issue. >>It seems that the issue is rising from pylsqpack. >>When the value field in the packet header for HTTP3 GET request contains >>long strings there are problems while encoding (Only in s390x). >>Due to this one of the GET parameters gets jumbled and this results in a bad >>request. >>I am not able to see the same issue on ls-qpack though. >>I will update any new findings. > >Yes, I was just going through this today (I hadn't noticed your emails >until after I'd spent some time on it) and I found much the same >thing. I reduced it to the following more manageable test case: > > # amd64 > >>> import pylsqpack > >>> encoder = pylsqpack.Encoder() > >>> decoder = pylsqpack.Decoder(4096, 16) > >>> _, frame = encoder.encode(0, [(b':path', > b'/dns-query?dns=AAABAAABAAAAAAAAAAABAAABAAAAAAAAA2RucwZnb29nbGUAAAEAAQ')]) > >>> decoder.feed_header(0, frame) > (b'', [(b':path', > b'/dns-query?dns=AAABAAABAAAAAAAAAAABAAABAAAAAAAAA2RucwZnb29nbGUAAAEAAQ')]) > > # s390x > >>> import pylsqpack > >>> encoder = pylsqpack.Encoder() > >>> decoder = pylsqpack.Decoder(4096, 16) > >>> _, frame = encoder.encode(0, [(b':path', > b'/dns-query?dns=AAABAAABAAAAAAAAAAABAAABAAAAAAAAA2RucwZnb29nbGUAAAEAAQ')]) > >>> decoder.feed_header(0, frame) > (b'', [(b':path', > b'd/snq-euyrd?snA=AAABAAABAAAAAAAAAAABAAABAAAAAAAAR2cuZwbn92bnUGAAAEAAQ')]) How does the attached patch look? The basic problem is that the Huffman encoder was assuming little-endian when reading from the source buffer. I realize this is against vendored code, but upstream ls-qpack seems to have pretty much the same code in this area, so if this looks good I'll tidy it up and submit it there. Thanks, -- Colin Watson (he/him) [cjwat...@debian.org]
diff --git a/vendor/ls-qpack/lsqpack.c b/vendor/ls-qpack/lsqpack.c index de125e0..693df8a 100644 --- a/vendor/ls-qpack/lsqpack.c +++ b/vendor/ls-qpack/lsqpack.c @@ -37,6 +37,7 @@ SOFTWARE. #include <string.h> #include <sys/queue.h> #include <sys/types.h> +#include <endian.h> #include <inttypes.h> #include "lsqpack.h"
