osmocom
/
wireshark
14
0
Fork 1
Code Issues Pull Requests Projects Releases Wiki Activity

Add a note about doing checks before subtracting, for example, the 

length of a fixed-length header from the length of the item with that
fixed-length header.

svn path=/trunk/; revision=13926
This commit is contained in:
Guy Harris 2005-03-26 23:31:35 +00:00
parent c1967f8152
commit 6cacd26f20
1 changed files with 12 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
doc/README.developer
View File

@ -400,6 +400,18 @@ the length was added to it, if the length field is greater than 24 bits
long, so that, if the length value is *very* large and adding it to the
offset causes an overflow, that overflow is detected.
If you are fetching a length field from the buffer, corresponding to the
length of a portion of the packet, and subtracting from that length a
value corresponding to the length of, for example, a header in the
packet portion in question, *ALWAYS* check that the value of the length
field is greater than or equal to the length you're subtracting from it,
and report an error in the packet and stop dissecting the packet if it's
less than the length you're subtracting from it. Otherwise, the
resulting length value will be negative, which will either cause errors
in the dissector or routines called by the dissector, or, if the value
is interpreted as an unsigned integer, will cause the value to be
interpreted as a very large positive value.
Any tvbuff offset that is added to as processing is done on a packet
should be stored in a 32-bit variable, such as an "int"; if you store it
in an 8-bit or 16-bit variable, you run the risk of the variable