[cfe-dev] [RFC] Adding warnings against usage of %n

[Jayson Yan via cfe-dev]

Hello everyone,

We’re interested in warning against the usage of the “%n” format string
specifier to discourage developers from using this potentially unsafe
format specifier.

We were thinking of enabling this as a warning under the -Wformat-security
flag but are open to alternatives, some ideas were:

   -

   Placing this check under its own flag (something along the lines of
   “-Wformat-n”) and possibly enabling it with -Wformat or -Wformat-security


   -

   Adding a check to clang-tidy
   -

   Setting the default configuration based on the target triple (target
   runtimes may disallow %n altogether and we could detect this based on the
   target triple)


Interested in any thoughts on:

   -

   How should we enable this? (eg. flags, clang-tidy, etc)
   -

   Should we surface this as an error or a warning?


Thanks,
Jayson
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