On Fri, 27 May 2016 23:23:25 +0200 Arnd Bergmann <arnd@xxxxxxxx> wrote: > Most users of IS_ERR_VALUE() in the kernel are wrong, as they > pass an 'int' into a function that takes an 'unsigned long' > argument. This happens to work because the type is sign-extended > on 64-bit architectures before it gets converted into an > unsigned type. > > However, anything that passes an 'unsigned short' or 'unsigned int' > argument into IS_ERR_VALUE() is guaranteed to be broken, as are > 8-bit integers and types that are wider than 'unsigned long'. > > Andrzej Hajda has already fixed a lot of the worst abusers that > were causing actual bugs, but it would be nice to prevent any > users that are not passing 'unsigned long' arguments. > > This patch changes all users of IS_ERR_VALUE() that I could find > on 32-bit ARM randconfig builds and x86 allmodconfig. For the > moment, this doesn't change the definition of IS_ERR_VALUE() > because there are probably still architecture specific users > elsewhere. So you do plan to add some sort of typechecking into IS_ERR_VALUE()? > Almost all the warnings I got are for files that are better off > using 'if (err)' or 'if (err < 0)'. > The only legitimate user I could find that we get a warning for > is the (32-bit only) freescale fman driver, so I did not remove > the IS_ERR_VALUE() there but changed the type to 'unsigned long'. > For 9pfs, I just worked around one user whose calling conventions > are so obscure that I did not dare change the behavior. > > I was using this definition for testing: > > #define IS_ERR_VALUE(x) ((unsigned long*)NULL == (typeof (x)*)NULL && \ > unlikely((unsigned long long)(x) >= (unsigned long long)(typeof(x))-MAX_ERRNO)) > > which ends up making all 16-bit or wider types work correctly with > the most plausible interpretation of what IS_ERR_VALUE() was supposed > to return according to its users, but also causes a compile-time > warning for any users that do not pass an 'unsigned long' argument. > > I suggested this approach earlier this year, but back then we ended > up deciding to just fix the users that are obviously broken. After > the initial warning that caused me to get involved in the discussion > (fs/gfs2/dir.c) showed up again in the mainline kernel, Linus > asked me to send the whole thing again. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
