From: Dave Johnson Date: Wed, 18 Apr 2007 14:39:41 +0000 (-0400) Subject: [MIPS] Fix wrong checksum for split TCP packets on 64-bit MIPS X-Git-Tag: v2.6.21~37^2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1d464c26b5625215c4b35fb336c8f3c57d248c2e;p=linux-2.6 [MIPS] Fix wrong checksum for split TCP packets on 64-bit MIPS I've traced down an off-by-one TCP checksum calculation error under the following conditions: 1) The TCP code needs to split a full-sized packet due to a reduced MSS (typically due to the addition of TCP options mid-stream like SACK). _AND_ 2) The checksum of the 2nd fragment is larger than the checksum of the original packet. After subtraction this results in a checksum for the 1st fragment with bits 16..31 set to 1. (this is ok) _AND_ 3) The checksum of the 1st fragment's TCP header plus the previously 32bit checksum of the 1st fragment DOES NOT cause a 32bit overflow when added together. This results in a checksum of the TCP header plus TCP data that still has the upper 16 bits as 1's. _THEN_ 4) The TCP+data checksum is added to the checksum of the pseudo IP header with csum_tcpudp_nofold() incorrectly (the bug). The problem is the checksum of the TCP+data is passed to csum_tcpudp_nofold() as an 32bit unsigned value, however the assembly code acts on it as if it is a 64bit unsigned value. This causes an incorrect 32->64bit extension if the sum has bit 31 set. The resulting checksum is off by one. This problems is data and TCP header dependent due to #2 and #3 above so it doesn't occur on every TCP packet split. Signed-off-by: Dave Johnson Signed-off-by: Ralf Baechle --- diff --git a/include/asm-mips/checksum.h b/include/asm-mips/checksum.h index 20a81e1548..290485ac54 100644 --- a/include/asm-mips/checksum.h +++ b/include/asm-mips/checksum.h @@ -166,7 +166,7 @@ static inline __wsum csum_tcpudp_nofold(__be32 saddr, #else "r" (proto + len), #endif - "r" (sum)); + "r" ((__force unsigned long)sum)); return sum; }