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Date: Sat, 4 Jan 2014 11:26:22 +0900 From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> To: keescook@...omium.org, joe@...ches.com, pavel@....cz Cc: akpm@...ux-foundation.org, geert@...ux-m68k.org, jkosina@...e.cz, viro@...iv.linux.org.uk, davem@...emloft.net, linux-kernel@...r.kernel.org Subject: Re: [PATCH] lib/vsprintf: add %pT[C012] format specifier I'm planning to convert task_struct->comm to use RCU so that they always get consistent result. Inconsistent result (e.g. trailing '\0' byte is emitted when printing string argument) is caused by breaking a rule that the string argument must not change during the function when it is passed as "const char *" (e.g. strcmp() and printf("%s")). Although task_struct->comm is not modified so frequently, task_struct->comm passed as a "const char *" argument can change at any moment unless we pass task_struct->comm via get_task_comm(). Since there are a lot of current->comm readers, Andrew Morton suggested that we might be able to omit passing the argument and I wrote a patch that adds a second format-start character for omit passing the argument. Kees Cook wrote: > I'm on board with the idea of embedding comm/pid/whatever, but I > either missed or do not understand why a second format-start character > is being added. I think this will complicate audits and maybe trigger > weird info leaks (imagine printing a string that was %-escaped, but > not 0x1A-escaped?) The second format-start character applies to only format string. If we use a dynamically generated string that was %-escaped at run-time as a format string, we will leak globally accessible variables. But are there such users? Such users are rare because they are already problematic since compilers cannot check for safety using __printf() attributes at build-time. > Hrmpf. Yeah, on the fence about this. But I'm fine even if we cannot agree with the second format-start character. Since my purpose is to make reading of task_struct->comm consistent, %pT-like extension is what I want for centralizing pointer dereferences. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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