Off-by-one problem (maximum non-data Twrite message size is 23, not 24) #1
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The manpage describes Twrite as: size[4] Twrite tag[2] fid[4] offset[8] count[4] data[count] if count = 0, the message size is 4 + 1 + 2 + 4 + 8 + 4 = 23 This manifests as a bug if a client agrees a maximum message size with a server, and then computes the maximum value for `count` by subtracting 23 i.e. the biggest possible write message. If the server then checks whether the request is too big by subtracting 24, it will return an error. Signed-off-by: David Scott <[email protected]>
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I've been debugging my 9P implementation [djs55/ocaml-9p] against go9p and noticed a difference in the write message handling. If I'm reading the spec correctly then I think there's an off-by-one in go9p. What do you think?
The manpage describes Twrite as:
size[4] Twrite tag[2] fid[4] offset[8] count[4] data[count]
if count = 0, the message size is 4 + 1 + 2 + 4 + 8 + 4 = 23
This manifests as a bug if a client agrees a maximum message size
with a server, and then computes the maximum value for
countby subtracting 23 i.e. the biggest possible write message. If the
server then checks whether the request is too big by subtracting
24, it will return an error.
Signed-off-by: David Scott [email protected]