| From 624f5ab8720b3371367327a822c267699c1823b8 Mon Sep 17 00:00:00 2001 |
| From: Eric Biggers <ebiggers@google.com> |
| Date: Tue, 7 Nov 2017 22:29:02 +0000 |
| Subject: KEYS: fix NULL pointer dereference during ASN.1 parsing [ver #2] |
| |
| From: Eric Biggers <ebiggers@google.com> |
| |
| commit 624f5ab8720b3371367327a822c267699c1823b8 upstream. |
| |
| syzkaller reported a NULL pointer dereference in asn1_ber_decoder(). It |
| can be reproduced by the following command, assuming |
| CONFIG_PKCS7_TEST_KEY=y: |
| |
| keyctl add pkcs7_test desc '' @s |
| |
| The bug is that if the data buffer is empty, an integer underflow occurs |
| in the following check: |
| |
| if (unlikely(dp >= datalen - 1)) |
| goto data_overrun_error; |
| |
| This results in the NULL data pointer being dereferenced. |
| |
| Fix it by checking for 'datalen - dp < 2' instead. |
| |
| Also fix the similar check for 'dp >= datalen - n' later in the same |
| function. That one possibly could result in a buffer overread. |
| |
| The NULL pointer dereference was reproducible using the "pkcs7_test" key |
| type but not the "asymmetric" key type because the "asymmetric" key type |
| checks for a 0-length payload before calling into the ASN.1 decoder but |
| the "pkcs7_test" key type does not. |
| |
| The bug report was: |
| |
| BUG: unable to handle kernel NULL pointer dereference at (null) |
| IP: asn1_ber_decoder+0x17f/0xe60 lib/asn1_decoder.c:233 |
| PGD 7b708067 P4D 7b708067 PUD 7b6ee067 PMD 0 |
| Oops: 0000 [#1] SMP |
| Modules linked in: |
| CPU: 0 PID: 522 Comm: syz-executor1 Not tainted 4.14.0-rc8 #7 |
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.3-20171021_125229-anatol 04/01/2014 |
| task: ffff9b6b3798c040 task.stack: ffff9b6b37970000 |
| RIP: 0010:asn1_ber_decoder+0x17f/0xe60 lib/asn1_decoder.c:233 |
| RSP: 0018:ffff9b6b37973c78 EFLAGS: 00010216 |
| RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000000021c |
| RDX: ffffffff814a04ed RSI: ffffb1524066e000 RDI: ffffffff910759e0 |
| RBP: ffff9b6b37973d60 R08: 0000000000000001 R09: ffff9b6b3caa4180 |
| R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002 |
| R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 |
| FS: 00007f10ed1f2700(0000) GS:ffff9b6b3ea00000(0000) knlGS:0000000000000000 |
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| CR2: 0000000000000000 CR3: 000000007b6f3000 CR4: 00000000000006f0 |
| Call Trace: |
| pkcs7_parse_message+0xee/0x240 crypto/asymmetric_keys/pkcs7_parser.c:139 |
| verify_pkcs7_signature+0x33/0x180 certs/system_keyring.c:216 |
| pkcs7_preparse+0x41/0x70 crypto/asymmetric_keys/pkcs7_key_type.c:63 |
| key_create_or_update+0x180/0x530 security/keys/key.c:855 |
| SYSC_add_key security/keys/keyctl.c:122 [inline] |
| SyS_add_key+0xbf/0x250 security/keys/keyctl.c:62 |
| entry_SYSCALL_64_fastpath+0x1f/0xbe |
| RIP: 0033:0x4585c9 |
| RSP: 002b:00007f10ed1f1bd8 EFLAGS: 00000216 ORIG_RAX: 00000000000000f8 |
| RAX: ffffffffffffffda RBX: 00007f10ed1f2700 RCX: 00000000004585c9 |
| RDX: 0000000020000000 RSI: 0000000020008ffb RDI: 0000000020008000 |
| RBP: 0000000000000000 R08: ffffffffffffffff R09: 0000000000000000 |
| R10: 0000000000000000 R11: 0000000000000216 R12: 00007fff1b2260ae |
| R13: 00007fff1b2260af R14: 00007f10ed1f2700 R15: 0000000000000000 |
| Code: dd ca ff 48 8b 45 88 48 83 e8 01 4c 39 f0 0f 86 a8 07 00 00 e8 53 dd ca ff 49 8d 46 01 48 89 85 58 ff ff ff 48 8b 85 60 ff ff ff <42> 0f b6 0c 30 89 c8 88 8d 75 ff ff ff 83 e0 1f 89 8d 28 ff ff |
| RIP: asn1_ber_decoder+0x17f/0xe60 lib/asn1_decoder.c:233 RSP: ffff9b6b37973c78 |
| CR2: 0000000000000000 |
| |
| Fixes: 42d5ec27f873 ("X.509: Add an ASN.1 decoder") |
| Reported-by: syzbot <syzkaller@googlegroups.com> |
| Signed-off-by: Eric Biggers <ebiggers@google.com> |
| Signed-off-by: David Howells <dhowells@redhat.com> |
| Signed-off-by: James Morris <james.l.morris@oracle.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| lib/asn1_decoder.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/lib/asn1_decoder.c |
| +++ b/lib/asn1_decoder.c |
| @@ -228,7 +228,7 @@ next_op: |
| hdr = 2; |
| |
| /* Extract a tag from the data */ |
| - if (unlikely(dp >= datalen - 1)) |
| + if (unlikely(datalen - dp < 2)) |
| goto data_overrun_error; |
| tag = data[dp++]; |
| if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) |
| @@ -274,7 +274,7 @@ next_op: |
| int n = len - 0x80; |
| if (unlikely(n > 2)) |
| goto length_too_long; |
| - if (unlikely(dp >= datalen - n)) |
| + if (unlikely(n > datalen - dp)) |
| goto data_overrun_error; |
| hdr += n; |
| for (len = 0; n > 0; n--) { |