From: Eric Biggers ebiggers@google.com

In rsa_get_n(), if the buffer contained all 0's and "FIPS mode" is enabled, we would read one byte past the end of the buffer while scanning the leading zeroes. Fix it by checking 'n_sz' before '!*ptr'.

This bug was reachable by adding a specially crafted key of type "asymmetric" (requires CONFIG_RSA and CONFIG_X509_CERTIFICATE_PARSER).

KASAN report:

BUG: KASAN: slab-out-of-bounds in rsa_get_n+0x19e/0x1d0 crypto/rsa_helper.c:33 Read of size 1 at addr ffff88003501a708 by task keyctl/196

CPU: 1 PID: 196 Comm: keyctl Not tainted 4.14.0-09238-g1d3b78bbc6e9 #26 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014 Call Trace: rsa_get_n+0x19e/0x1d0 crypto/rsa_helper.c:33 asn1_ber_decoder+0x82a/0x1fd0 lib/asn1_decoder.c:328 rsa_set_pub_key+0xd3/0x320 crypto/rsa.c:278 crypto_akcipher_set_pub_key ./include/crypto/akcipher.h:364 [inline] pkcs1pad_set_pub_key+0xae/0x200 crypto/rsa-pkcs1pad.c:117 crypto_akcipher_set_pub_key ./include/crypto/akcipher.h:364 [inline] public_key_verify_signature+0x270/0x9d0 crypto/asymmetric_keys/public_key.c:106 x509_check_for_self_signed+0x2ea/0x480 crypto/asymmetric_keys/x509_public_key.c:141 x509_cert_parse+0x46a/0x620 crypto/asymmetric_keys/x509_cert_parser.c:129 x509_key_preparse+0x61/0x750 crypto/asymmetric_keys/x509_public_key.c:174 asymmetric_key_preparse+0xa4/0x150 crypto/asymmetric_keys/asymmetric_type.c:388 key_create_or_update+0x4d4/0x10a0 security/keys/key.c:850 SYSC_add_key security/keys/keyctl.c:122 [inline] SyS_add_key+0xe8/0x290 security/keys/keyctl.c:62 entry_SYSCALL_64_fastpath+0x1f/0x96

Allocated by task 196: __do_kmalloc mm/slab.c:3711 [inline] __kmalloc_track_caller+0x118/0x2e0 mm/slab.c:3726 kmemdup+0x17/0x40 mm/util.c:118 kmemdup ./include/linux/string.h:414 [inline] x509_cert_parse+0x2cb/0x620 crypto/asymmetric_keys/x509_cert_parser.c:106 x509_key_preparse+0x61/0x750 crypto/asymmetric_keys/x509_public_key.c:174 asymmetric_key_preparse+0xa4/0x150 crypto/asymmetric_keys/asymmetric_type.c:388 key_create_or_update+0x4d4/0x10a0 security/keys/key.c:850 SYSC_add_key security/keys/keyctl.c:122 [inline] SyS_add_key+0xe8/0x290 security/keys/keyctl.c:62 entry_SYSCALL_64_fastpath+0x1f/0x96

Fixes: 5a7de97309f5 ("crypto: rsa - return raw integers for the ASN.1 parser") Cc: stable@vger.kernel.org # v4.8+ Cc: Tudor Ambarus tudor-dan.ambarus@nxp.com Signed-off-by: Eric Biggers ebiggers@google.com --- crypto/rsa_helper.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/rsa_helper.c b/crypto/rsa_helper.c index 0b66dc824606..cad395d70d78 100644 --- a/crypto/rsa_helper.c +++ b/crypto/rsa_helper.c @@ -30,7 +30,7 @@ int rsa_get_n(void *context, size_t hdrlen, unsigned char tag, return -EINVAL;

if (fips_enabled) { - while (!*ptr && n_sz) { + while (n_sz && !*ptr) { ptr++; n_sz--; }