• Eric Biggers's avatar
    crypto: rsa - fix buffer overread when stripping leading zeroes · cd9b5986
    Eric Biggers authored
    commit d2890c37 upstream.
    
    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-g1d3b78bb #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: 5a7de973 ("crypto: rsa - return raw integers for the ASN.1 parser")
    Cc: Tudor Ambarus <tudor-dan.ambarus@nxp.com>
    Signed-off-by: 's avatarEric Biggers <ebiggers@google.com>
    Reviewed-by: 's avatarJames Morris <james.l.morris@oracle.com>
    Reviewed-by: 's avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: 's avatarHerbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    cd9b5986