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lib/vsprintf.c: fix potential NULL deref in hex_string

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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]>
Acked-by: Andy Shevchenko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Rasmus Villemoes 2015-04-15 16:17:23 -07:00 • committed by Linus Torvalds
commit 9c98f23596
1 changed files with 12 additions and 4 deletions
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16
lib/vsprintf.c
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@ -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;