Hi,
On Tue, Oct 25, 2011 at 4:42 PM, Simon Glass sjg@chromium.org wrote:
The printf family of functions in U-Boot cannot deal with a situation where the caller provides a buffer which turns out to be too small for the format string. This can result in buffer overflows, stack overflows and other bad behavior.
This patch series tidies this up in the common vsprintf.c code.
You can find a discussion of the Linux / U-Boot licensing issues here:
http://patchwork.ozlabs.org/patch/116161/
Code Size Impact
(From Simon Glass sjg@chromium.org) With my ARMv7 compiler (gcc-4.4.3_cos_gg_53174) the code size increase is 312 bytes, about 10% increase to code size vsprintf.o.
With the CONFIG_SYS_NO_VSNPRINT option defined, the code size impact is 4 bytes.
Changes in v2:
- Use sizeof(printbuffer) instead of CONFIG_SYS_PBSIZE
- Drop patch which changes network code to use snprintf()
Changes in v3:
- Move prototypes from common.h to vsprintf.h
- Add CONFIG_SYS_VSNPRINT option to enable vsnprintf() functions
- Update README with CONFIG_SYS_VSNPRINT docs
- Use ADDCH macro to support checking/not checking end pointer
- Move function documentation into header file
Changes in v4:
- Add these changes in unless CONFIG_NO_SYS_VSNPRINT is defined
- Reduce code size overhead if disabled to only 4 bytes on ARM
- Remove the ugly #ifdef patch from series since it only saves 4 bytes
Changes in v5:
- Define INT_MAX locally within vsprintf.c
- Drop limits.h as it is used in only two places in U-Boot
Simon Glass (2): Move vsprintf functions into their own header vsprintf: Move function documentation into header file
Sonny Rao (2): Add safe vsnprintf and snprintf library functions Make printf and vprintf safe from buffer overruns
Any more comments on this?
I have suggested making these functions available by default, and having CONFIG_NO_SYS_VSNPRINT to remove them. The rationale is that it if CONFIG_NO_SYS_VSNPRINT is not defined, then snprintf() will not check the buffer length (all the code to do it is removed), and this is unexpected. In this case snprintf() is #defined to sprintf().
There is therefore a code size increase by default with this series. We can instead use CONFIG_SYS_VSNPRINT if people think it is safe.
Regards, Simon
README | 7 ++ common/console.c | 10 +- include/common.h | 10 +-- include/vsprintf.h | 180 +++++++++++++++++++++++++++++++++++++++ lib/vsprintf.c | 237 ++++++++++++++++++++++++++++++++------------------- 5 files changed, 342 insertions(+), 102 deletions(-) create mode 100644 include/vsprintf.h
-- 1.7.3.1