Commit 9c98f235 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Linus Torvalds

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: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 900cca29
...@@ -777,11 +777,19 @@ char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec, ...@@ -777,11 +777,19 @@ char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
if (spec.field_width > 0) if (spec.field_width > 0)
len = min_t(int, spec.field_width, 64); len = min_t(int, spec.field_width, 64);
for (i = 0; i < len && buf < end - 1; i++) { for (i = 0; i < len; ++i) {
buf = hex_byte_pack(buf, addr[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) if (separator && i != len - 1) {
*buf++ = separator; if (buf < end)
*buf = separator;
++buf;
}
} }
return buf; return buf;
......
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