The helper hex_string() is broken in two ways. First, it doesn't increment buf regardless of whether there is room to print, so callers such as kasprintf() that try to probe the correct storage to allocate will get a too small return value. But even worse, kasprintf() (and likely anyone else trying to find the size of the result) pass NULL for buf and 0 for size, so we also have end == NULL. But this means that the end-1 in hex_string() is (char*)-1, so buf < end-1 is true and we get a NULL pointer deref. I double-checked this with a trivial kernel module that just did a kasprintf(GFP_KERNEL, "%14ph", "CrashBoomBang").
Nobody seems to be using %ph with kasprintf, but we might as well fix it before it hits someone. Signed-off-by: Rasmus Villemoes <[email protected]> --- lib/vsprintf.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index ec337f64f52d..0d57be58448f 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -748,11 +748,19 @@ char *resource_string(char *buf, char *end, struct resource *res, return string(buf, end, sym, spec); } +static char* +write_bytes(char *buf, char *end, const char *bytes, unsigned count) +{ + if (buf < end) + memcpy(buf, bytes, min_t(unsigned, end - buf, count)); + return buf + count; +} + static noinline_for_stack char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec, const char *fmt) { - int i, len = 1; /* if we pass '%ph[CDN]', field width remains + int i, j, len = 1; /* if we pass '%ph[CDN]', field width remains negative value, fallback to the default */ char separator; @@ -782,11 +790,16 @@ char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec, if (spec.field_width > 0) len = min_t(int, spec.field_width, 64); - for (i = 0; i < len && buf < end - 1; i++) { - buf = hex_byte_pack(buf, addr[i]); + for (i = 0; i < len; i += 8) { + char tmp[24]; /* 8*2 hex chars + 8 separators */ + char *t = tmp; - if (buf < end && separator && i != len - 1) - *buf++ = separator; + for (j = i; j < len && j < i+8; ++j) { + t = hex_byte_pack(t, addr[j]); + if (separator && j != len-1) + *t++ = separator; + } + buf = write_bytes(buf, end, tmp, t - tmp); } return buf; -- 2.1.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
