0f30cbea00
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>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.