6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Lukas Wunner lukas@wunner.de
[ Upstream commit 3b0565c703503f832d6cd7ba805aafa3b330cb9d ]
When extracting a signature component r or s from an ASN.1-encoded integer, ecdsa_get_signature_rs() subtracts the expected length "bufsize" from the ASN.1 length "vlen" (both of unsigned type size_t) and stores the result in "diff" (of signed type ssize_t).
This results in a signed integer overflow if vlen > SSIZE_MAX + bufsize.
The kernel is compiled with -fno-strict-overflow, which implies -fwrapv, meaning signed integer overflow is not undefined behavior. And the function does check for overflow:
if (-diff >= bufsize) return -EINVAL;
So the code is fine in principle but not very obvious. In the future it might trigger a false-positive with CONFIG_UBSAN_SIGNED_WRAP=y.
Avoid by comparing the two unsigned variables directly and erroring out if "vlen" is too large.
Signed-off-by: Lukas Wunner lukas@wunner.de Reviewed-by: Stefan Berger stefanb@linux.ibm.com Reviewed-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: Sasha Levin sashal@kernel.org --- crypto/ecdsa.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index 28441311af36..da04df3c8ecf 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -36,29 +36,24 @@ static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag, const void *value, size_t vlen, unsigned int ndigits) { size_t bufsize = ndigits * sizeof(u64); - ssize_t diff = vlen - bufsize; const char *d = value;
- if (!value || !vlen) + if (!value || !vlen || vlen > bufsize + 1) return -EINVAL;
- /* diff = 0: 'value' has exacly the right size - * diff > 0: 'value' has too many bytes; one leading zero is allowed that - * makes the value a positive integer; error on more - * diff < 0: 'value' is missing leading zeros + /* + * vlen may be 1 byte larger than bufsize due to a leading zero byte + * (necessary if the most significant bit of the integer is set). */ - if (diff > 0) { + if (vlen > bufsize) { /* skip over leading zeros that make 'value' a positive int */ if (*d == 0) { vlen -= 1; - diff--; d++; - } - if (diff) + } else { return -EINVAL; + } } - if (-diff >= bufsize) - return -EINVAL;
ecc_digits_from_bytes(d, vlen, dest, ndigits);