sanitizes user-supplied printf(3)-style format
fmtcheck function scans
fmt_suspect and fmt_default to
determine if fmt_suspect will consume the same
argument types as fmt_default and to ensure that
fmt_suspect is a valid format string.
The printf(3) family of functions can not verify the types of arguments that they are passed at run-time. In some cases, like catgets(3), it is useful or necessary to use a user-supplied format string with no guarantee that the format string matches the specified parameters.
fmtcheck function was designed to be
used in these cases, as in:
printf(fmtcheck(user_format, standard_format), arg1, arg2);
In the check, field widths, fillers, precisions, etc. are ignored
(unless the field width or precision is an asterisk
*’ instead of a digit string). Also,
any text other than the format specifiers is completely ignored.
Note that the formats may be quite different as long as they accept the same parameters. For example, "%ld %o %30s %#llx %-10.*e %n" is compatible with "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)." However, "%o" is not equivalent to "%lx" because the first requires an integer and the second requires a long, and "%p" is not equivalent to "%lu" because the first requires a pointer and the second requires a long.
If fmt_suspect is a valid format and
consumes the same argument types as fmt_default, then
fmtcheck function will return
fmt_suspect. Otherwise, it will return
|June 14, 2014||Linux 6.3.2-arch1-1|