From: Eric Biggers ebiggers@google.com
In asn1_ber_decoder(), indefinitely-sized ASN.1 items were being passed to the action functions before their lengths had been computed, using the bogus length of 0x80 (ASN1_INDEFINITE_LENGTH). This resulted in reading data past the end of the input buffer, when given a specially crafted message.
Fix it by rearranging the code so that the indefinite length is resolved before the action is called.
This bug was originally found by fuzzing the X.509 parser in userspace using libFuzzer from the LLVM project.
KASAN report (cleaned up slightly):
BUG: KASAN: slab-out-of-bounds in memcpy ./include/linux/string.h:341 [inline] BUG: KASAN: slab-out-of-bounds in x509_fabricate_name.constprop.1+0x1a4/0x940 crypto/asymmetric_keys/x509_cert_parser.c:366 Read of size 128 at addr ffff880035dd9eaf by task keyctl/195
CPU: 1 PID: 195 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: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0xd1/0x175 lib/dump_stack.c:53 print_address_description+0x78/0x260 mm/kasan/report.c:252 kasan_report_error mm/kasan/report.c:351 [inline] kasan_report+0x23f/0x350 mm/kasan/report.c:409 memcpy+0x1f/0x50 mm/kasan/kasan.c:302 memcpy ./include/linux/string.h:341 [inline] x509_fabricate_name.constprop.1+0x1a4/0x940 crypto/asymmetric_keys/x509_cert_parser.c:366 asn1_ber_decoder+0xb4a/0x1fd0 lib/asn1_decoder.c:447 x509_cert_parse+0x1c7/0x620 crypto/asymmetric_keys/x509_cert_parser.c:89 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 195: __do_kmalloc_node mm/slab.c:3675 [inline] __kmalloc_node+0x47/0x60 mm/slab.c:3682 kvmalloc ./include/linux/mm.h:540 [inline] SYSC_add_key security/keys/keyctl.c:104 [inline] SyS_add_key+0x19e/0x290 security/keys/keyctl.c:62 entry_SYSCALL_64_fastpath+0x1f/0x96
Fixes: 42d5ec27f873 ("X.509: Add an ASN.1 decoder") Reported-by: Alexander Potapenko glider@google.com Cc: stable@vger.kernel.org # v3.7+ Signed-off-by: Eric Biggers ebiggers@google.com --- lib/asn1_decoder.c | 47 ++++++++++++++++++++++++++--------------------- 1 file changed, 26 insertions(+), 21 deletions(-)
diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c index 1ef0cec38d78..d77cdfc4b554 100644 --- a/lib/asn1_decoder.c +++ b/lib/asn1_decoder.c @@ -313,42 +313,47 @@ int asn1_ber_decoder(const struct asn1_decoder *decoder,
/* Decide how to handle the operation */ switch (op) { - case ASN1_OP_MATCH_ANY_ACT: - case ASN1_OP_MATCH_ANY_ACT_OR_SKIP: - case ASN1_OP_COND_MATCH_ANY_ACT: - case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP: - ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len); - if (ret < 0) - return ret; - goto skip_data; - - case ASN1_OP_MATCH_ACT: - case ASN1_OP_MATCH_ACT_OR_SKIP: - case ASN1_OP_COND_MATCH_ACT_OR_SKIP: - ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len); - if (ret < 0) - return ret; - goto skip_data; - case ASN1_OP_MATCH: case ASN1_OP_MATCH_OR_SKIP: + case ASN1_OP_MATCH_ACT: + case ASN1_OP_MATCH_ACT_OR_SKIP: case ASN1_OP_MATCH_ANY: case ASN1_OP_MATCH_ANY_OR_SKIP: + case ASN1_OP_MATCH_ANY_ACT: + case ASN1_OP_MATCH_ANY_ACT_OR_SKIP: case ASN1_OP_COND_MATCH_OR_SKIP: + case ASN1_OP_COND_MATCH_ACT_OR_SKIP: case ASN1_OP_COND_MATCH_ANY: case ASN1_OP_COND_MATCH_ANY_OR_SKIP: - skip_data: + case ASN1_OP_COND_MATCH_ANY_ACT: + case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP: + if (!(flags & FLAG_CONS)) { if (flags & FLAG_INDEFINITE_LENGTH) { + size_t tmp = dp; + ret = asn1_find_indefinite_length( - data, datalen, &dp, &len, &errmsg); + data, datalen, &tmp, &len, &errmsg); if (ret < 0) goto error; - } else { - dp += len; } pr_debug("- LEAF: %zu\n", len); } + + if (op & ASN1_OP_MATCH__ACT) { + unsigned char act; + + if (op & ASN1_OP_MATCH__ANY) + act = machine[pc + 1]; + else + act = machine[pc + 2]; + ret = actions[act](context, hdr, tag, data + dp, len); + if (ret < 0) + return ret; + } + + if (!(flags & FLAG_CONS)) + dp += len; pc += asn1_op_lengths[op]; goto next_op;