From: Rasmus Villemoes Date: Wed, 15 Apr 2015 23:17:23 +0000 (-0700) Subject: lib/vsprintf.c: fix potential NULL deref in hex_string X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=9c98f2359600386efd1c6adfabc5a04118a79798;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git lib/vsprintf.c: fix potential NULL deref in hex_string 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 Acked-by: Andy Shevchenko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 3ab8c9cf3980..4da1e7aaf9d5 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -777,11 +777,19 @@ 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) { + if (buf < end) + *buf = hex_asc_hi(addr[i]); + ++buf; + if (buf < end) + *buf = hex_asc_lo(addr[i]); + ++buf; - if (buf < end && separator && i != len - 1) - *buf++ = separator; + if (separator && i != len - 1) { + if (buf < end) + *buf = separator; + ++buf; + } } return buf;