From: Eric Biggers ebiggers@google.com

Adding a specially crafted X.509 certificate whose subjectPublicKey ASN.1 value is zero-length caused x509_extract_key_data() to set the public key size to SIZE_MAX, as it subtracted the nonexistent BIT STRING metadata byte. Then, x509_cert_parse() called kmemdup() with that bogus size, triggering the WARN_ON_ONCE() in kmalloc_slab().

This appears to be harmless, but it still must be fixed since WARNs are never supposed to be user-triggerable.

Fix it by updating x509_cert_parse() to validate that the value has a BIT STRING metadata byte, and that the byte is 0 which indicates that the number of bits in the bitstring is a multiple of 8.

It would be nice to handle the metadata byte in asn1_ber_decoder() instead. But that would be tricky because in the general case a BIT STRING could be implicitly tagged, and/or could legitimately have a length that is not a whole number of bytes.

Here was the WARN (cleaned up slightly):

WARNING: CPU: 1 PID: 202 at mm/slab_common.c:971 kmalloc_slab+0x5d/0x70 mm/slab_common.c:971 Modules linked in: CPU: 1 PID: 202 Comm: keyctl Tainted: G B 4.14.0-09238-g1d3b78bbc6e9 #26 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014 task: ffff880033014180 task.stack: ffff8800305c8000 Call Trace: __do_kmalloc mm/slab.c:3706 [inline] __kmalloc_track_caller+0x22/0x2e0 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: 42d5ec27f873 ("X.509: Add an ASN.1 decoder") Cc: stable@vger.kernel.org # v3.7+ Signed-off-by: Eric Biggers ebiggers@google.com --- crypto/asymmetric_keys/x509_cert_parser.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c index dd03fead1ca3..ce2df8c9c583 100644 --- a/crypto/asymmetric_keys/x509_cert_parser.c +++ b/crypto/asymmetric_keys/x509_cert_parser.c @@ -409,6 +409,8 @@ int x509_extract_key_data(void *context, size_t hdrlen, ctx->cert->pub->pkey_algo = "rsa";

/* Discard the BIT STRING metadata */ + if (vlen < 1 || *(const u8 *)value != 0) + return -EBADMSG; ctx->key = value + 1; ctx->key_size = vlen - 1; return 0;