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authorUlrich Sibiller <uli42@gmx.de>2021-03-17 22:17:55 +0100
committerMike Gabriel <mike.gabriel@das-netzwerkteam.de>2021-06-08 08:23:35 +0200
commit2739d0868f849a186f7b06cb0032ee0d2c599532 (patch)
tree393bb9cefe5a82cd3da2e06d21d4a8dcdb300a14 /nx-X11/programs/Xserver/composite
parent3228dcfc5643e18bc7f115b7ac835267d13f42ee (diff)
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Compext.c: fix comparisons of 16bit sequence numbers
rep->generic.sequenceNumber is of type CARD16 state->sequence is of type unsigned long Converting state->sequence to an int as it has been done since the first version of nxcomp I know of (1.3.0-18 from 2003) is wrong here because for numbers > INT_MAX this will result in a negative number, which, after applying the 16bit modulo, will not match rep->generic.sequenceNumber. Example with numbers: CARD16 c = 24565 unsigned long u = 3179110389 c % 65536 = 24565 u % 65536 = 24565 (int)(u) = -1115856907 (int)(u) % 65536 = -40971 -40971 will not match 24565 To fix this we need to ensure the number stays positive. We use CARD16 for this to match the type in the request which is a 16bit number. On my system CARD16 is unsigned short which is guaranteed to contain _at least_ the 0-65,535 range. As there is no upper limit of the range we cannot drop the modulo because we need this value to be 16bit and not more. Thanks to Norm Green for providing log after log until we could finally identify the reason for him seeing "Xlib: unexpected async reply (sequence 0x94b01439)!" when pasting stopped working.
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