diff options
| author | Kees Cook | 2013-11-14 14:31:58 -0800 |
|---|---|---|
| committer | Linus Torvalds | 2013-11-15 09:32:20 +0900 |
| commit | 9196436ab2f713b823a2ba2024cb69f40b2f54a5 (patch) | |
| tree | d10e292c5e307d616edfa13345a6735ed3cc93c9 /lib | |
| parent | 652586df95e5d76b37d07a11839126dcfede1621 (diff) | |
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@chromium.org>
Cc: Joe Perches <joe@perches.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/vsprintf.c | 20 |
1 files changed, 9 insertions, 11 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 48586ac3a62e..10909c571494 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1712,18 +1712,16 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args) 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; } |