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crypto: ecc - Prevent ecc_digits_from_bytes from reading too many bytes

PATCH In review Stefan Berger 2 participants 2 messages May 21, 2024 – May 22, 2024

Subsystems (3)
Crypto API Keys/keyrings Asymmetric keys - ecdsa
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Stefan Berger

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PATCH v3 1/1 crypto: ecc - Prevent ecc_digits_from_bytes from reading too many bytes

Prevent ecc_digits_from_bytes from reading too many bytes from the input byte array in case an insufficient number of bytes is provided to fill the output digit array of ndigits. Therefore, initialize the most significant digits with 0 to avoid trying to read too many bytes later on. Convert the function into a regular function since it is getting too big for an inline function.

If too many bytes are provided on the input byte array the extra bytes are ignored since the input variable 'ndigits' limits the number of digits that will be filled.

Fixes d67c96fb97b5 ("crypto: ecdsa - Convert byte arrays with key coordinates to digits")
Reviewed-by Jarkko Sakkinen <[email protected]>
Signed-off-by Stefan Berger <[email protected]>

---
v3:
- Applied Jarkko's tag

v2:
- un-inline function
- use memset

---
 crypto/ecc.c                  | 22 ++++++++++++++++++++++
 include/crypto/internal/ecc.h | 15 ++-------------
 2 files changed, 24 insertions(+), 13 deletions(-)
crypto/ecc.c +22 -0
index c1d2e884be1e..fe761256e335 100644
@@ -68,6 +68,28 @@ const struct ecc_curve *ecc_get_curve(unsigned int curve_id)
 }
 EXPORT_SYMBOL(ecc_get_curve);
 
+void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
+			   u64 *out, unsigned int ndigits)
+{
+	int diff = ndigits - DIV_ROUND_UP(nbytes, sizeof(u64));
+	unsigned int o = nbytes & 7;
+	__be64 msd = 0;
+
+	/* diff > 0: not enough input bytes: set most significant digits to 0 */
+	if (diff > 0) {
+		ndigits -= diff;
+		memset(&out[ndigits - 1], 0, diff * sizeof(u64));
+	}
+
+	if (o) {
+		memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
+		out[--ndigits] = be64_to_cpu(msd);
+		in += o;
+	}
+	ecc_swap_digits(in, out, ndigits);
+}
+EXPORT_SYMBOL(ecc_digits_from_bytes);
+
 static u64 *ecc_alloc_digits_space(unsigned int ndigits)
 {
 	size_t len = ndigits * sizeof(u64);
include/crypto/internal/ecc.h +2 -13
index 7ca1f463d1ec..f7e75e1e71f3 100644
@@ -64,19 +64,8 @@ static inline void ecc_swap_digits(const void *in, u64 *out, unsigned int ndigit
  * @out       Output digits array
  * @ndigits:  Number of digits to create from byte array
  */
-static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
-					 u64 *out, unsigned int ndigits)
-{
-	unsigned int o = nbytes & 7;
-	__be64 msd = 0;
-
-	if (o) {
-		memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
-		out[--ndigits] = be64_to_cpu(msd);
-		in += o;
-	}
-	ecc_swap_digits(in, out, ndigits);
-}
+void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
+			   u64 *out, unsigned int ndigits);
 
 /**
  * ecc_is_key_valid() - Validate a given ECDH private key
Signature · 1 line
2.43.0
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#1 lore raw
Quoted 11 lines · Stefan Berger

Prevent ecc_digits_from_bytes from reading too many bytes from the input byte array in case an insufficient number of bytes is provided to fill the output digit array of ndigits. Therefore, initialize the most significant digits with 0 to avoid trying to read too many bytes later on. Convert the function into a regular function since it is getting too big for an inline function.

If too many bytes are provided on the input byte array the extra bytes are ignored since the input variable 'ndigits' limits the number of digits that will be filled.

Quoted 7 lines
Fixes d67c96fb97b5 ("crypto: ecdsa - Convert byte arrays with key coordinates to digits")
Reviewed-by Jarkko Sakkinen <[email protected]>
Signed-off-by Stefan Berger <[email protected]>

---
v3:
- Applied Jarkko's tag

Already landed in Linus' tree 42 hours ago -- with Jarkko's tag:

https://git.kernel.org/linus/568c98a0f6ef