RFC vsprintf: Do not dereference pointers in bstr_printf()

vbin_printf() and bstr_printf() are used by trace_printk(), when it is possible to optimize to copying the binary arguments into the ring buffer and doing the final conversions at the time of reading the ring buffer. This is advantageous as it removes computer processing from the executing of what's being traced, to the reading of the trace at a less critical time.

The issue is that the way the bprintk() works, as it records pointers at the time of execution, and then later dereferences those pointers when the buffer is being read. Things can change between these two events and bad pointers may be dereferenced.

In stead of just trying to avoid using vbin_printf() when using these pointers, as there is no use case for using it when dereferencing is can be an issue, have vbin_printf() and bstr_printf() either save the dereferenced information in vbin_printf() and print that out without the need to dereference at bstr_printf(), or simply output an error message saying that the dereference typo is unsupported.

This will prevent surprises while debugging with trace_printk().

The first patch adds the infrastructure to not support any of the dereferenced pointers. Then I added two patches to add support of %pf and %pb. The rest of the dereferenced pointers can be added at a later time, but I wanted to get people's feel for this change before going further on it.

Thoughts?

-- Steve

Steven Rostedt (Red Hat) (3):
vsprintf: Prevent vbin_printf() from using dereferenced pointers
vsprintf: Add support for %pf and %pF to vbin_printf()
vsprintf: Add support for %pb and friends to vbin_printf()

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 lib/vsprintf.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 118 insertions(+), 4 deletions(-)