Subject: [merged] vsprintf-ignore-%n-again.patch removed from -mm tree To: keescook@xxxxxxxxxxxx,davem@xxxxxxxxxxxxx,joe@xxxxxxxxxxx,penguin-kernel@xxxxxxxxxxxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Fri, 15 Nov 2013 12:08:59 -0800 The patch titled Subject: vsprintf: ignore %n again has been removed from the -mm tree. Its filename was vsprintf-ignore-%n-again.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Kees Cook <keescook@xxxxxxxxxxxx> Subject: vsprintf: ignore %n again This ignores %n in printf again, as was originally documented. Implementing %n poses a greater security risk than utility, so it should stay ignored. To help anyone attempting to use %n, a warning will be emitted if it is encountered. Based on an earlier patch by Joe Perches. Because %n was designed to write to pointers on the stack, it has been frequently used as an attack vector when bugs are found that leak user-controlled strings into functions that ultimately process format strings. While this class of bug can still be turned into an information leak, removing %n eliminates the common method of elevating such a bug into an arbitrary kernel memory writing primitive, significantly reducing the danger of this class of bug. For seq_file users that need to know the length of a written string for padding, please see seq_setwidth() and seq_pad() instead. Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Joe Perches <joe@xxxxxxxxxxx> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Cc: David Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/vsprintf.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-) diff -puN lib/vsprintf.c~vsprintf-ignore-%n-again lib/vsprintf.c --- a/lib/vsprintf.c~vsprintf-ignore-%n-again +++ a/lib/vsprintf.c @@ -1712,18 +1712,16 @@ int vsnprintf(char *buf, size_t size, co break; case FORMAT_TYPE_NRCHARS: { - u8 qualifier = spec.qualifier; + /* + * Since %n poses a greater security risk than + * utility, ignore %n and skip its argument. + */ + void *skip_arg; - if (qualifier == 'l') { - long *ip = va_arg(args, long *); - *ip = (str - buf); - } else if (_tolower(qualifier) == 'z') { - size_t *ip = va_arg(args, size_t *); - *ip = (str - buf); - } else { - int *ip = va_arg(args, int *); - *ip = (str - buf); - } + WARN_ONCE(1, "Please remove ignored %%n in '%s'\n", + old_fmt); + + skip_arg = va_arg(args, void *); break; } _ Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are origin.patch binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patch linux-next.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html