`iconv_sysctl_add` from `sys/libkern/iconv.c` incorrectly limits the
size of user strings, such that several out of bounds reads could have
been possible.
static int
iconv_sysctl_add(SYSCTL_HANDLER_ARGS)
{
struct iconv_converter_class *dcp;
struct iconv_cspair *csp;
struct iconv_add_in din;
struct iconv_add_out dout;
int error;
error = SYSCTL_IN(req, &din, sizeof(din));
if (error)
return error;
if (din.ia_version != ICONV_ADD_VER)
return EINVAL;
if (din.ia_datalen > ICONV_CSMAXDATALEN)
return EINVAL;
if (strlen(din.ia_from) >= ICONV_CSNMAXLEN)
return EINVAL;
if (strlen(din.ia_to) >= ICONV_CSNMAXLEN)
return EINVAL;
if (strlen(din.ia_converter) >= ICONV_CNVNMAXLEN)
return EINVAL;
...
Since the `din` struct is directly copied from userland, there is no
guarantee that the strings supplied will be NULL terminated. The
`strlen` calls could continue reading past the designated buffer
sizes.
Declaration of `struct iconv_add_in` is found in `sys/sys/iconv.h`:
struct iconv_add_in {
int ia_version;
char ia_converter[ICONV_CNVNMAXLEN];
char ia_to[ICONV_CSNMAXLEN];
char ia_from[ICONV_CSNMAXLEN];
int ia_datalen;
const void *ia_data;
};
Our strings are followed by the `ia_datalen` member, which is checked
before the `strlen` calls:
if (din.ia_datalen > ICONV_CSMAXDATALEN)
Since `ICONV_CSMAXDATALEN` has value `0x41000` (and is `unsigned`),
this ensures that `din.ia_datalen` contains at least 1 byte of 0, so
it is not possible to trigger a read out of bounds of the `struct`
however, this code is fragile and could introduce subtle bugs in the
future if the `struct` is ever modified.
PR: 207302
Submitted by: CTurt <cturt@hardenedbsd.org>
Reported by: CTurt <cturt@hardenedbsd.org>
Reviewed by: jhb, vangyzen
MFC after: 1 week
Sponsored by: Dell EMC
Differential Revision: https://reviews.freebsd.org/D14521
f000e33bcb