4.20-stable review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
commit 8f9c469348487844328e162db57112f7d347c49f upstream.
Keys for "authenc" AEADs are formatted as an rtattr containing a 4-byte 'enckeylen', followed by an authentication key and an encryption key. crypto_authenc_extractkeys() parses the key to find the inner keys.
However, it fails to consider the case where the rtattr's payload is longer than 4 bytes but not 4-byte aligned, and where the key ends before the next 4-byte aligned boundary. In this case, 'keylen -= RTA_ALIGN(rta->rta_len);' underflows to a value near UINT_MAX. This causes a buffer overread and crash during crypto_ahash_setkey().
Fix it by restricting the rtattr payload to the expected size.
Reproducer using AF_ALG:
#include <linux/if_alg.h> #include <linux/rtnetlink.h> #include <sys/socket.h>
int main() { int fd; struct sockaddr_alg addr = { .salg_type = "aead", .salg_name = "authenc(hmac(sha256),cbc(aes))", }; struct { struct rtattr attr; __be32 enckeylen; char keys[1]; } __attribute__((packed)) key = { .attr.rta_len = sizeof(key), .attr.rta_type = 1 /* CRYPTO_AUTHENC_KEYA_PARAM */, };
fd = socket(AF_ALG, SOCK_SEQPACKET, 0); bind(fd, (void *)&addr, sizeof(addr)); setsockopt(fd, SOL_ALG, ALG_SET_KEY, &key, sizeof(key)); }
It caused:
BUG: unable to handle kernel paging request at ffff88007ffdc000 PGD 2e01067 P4D 2e01067 PUD 2e04067 PMD 2e05067 PTE 0 Oops: 0000 [#1] SMP CPU: 0 PID: 883 Comm: authenc Not tainted 4.20.0-rc1-00108-g00c9fe37a7f27 #13 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014 RIP: 0010:sha256_ni_transform+0xb3/0x330 arch/x86/crypto/sha256_ni_asm.S:155 [...] Call Trace: sha256_ni_finup+0x10/0x20 arch/x86/crypto/sha256_ssse3_glue.c:321 crypto_shash_finup+0x1a/0x30 crypto/shash.c:178 shash_digest_unaligned+0x45/0x60 crypto/shash.c:186 crypto_shash_digest+0x24/0x40 crypto/shash.c:202 hmac_setkey+0x135/0x1e0 crypto/hmac.c:66 crypto_shash_setkey+0x2b/0xb0 crypto/shash.c:66 shash_async_setkey+0x10/0x20 crypto/shash.c:223 crypto_ahash_setkey+0x2d/0xa0 crypto/ahash.c:202 crypto_authenc_setkey+0x68/0x100 crypto/authenc.c:96 crypto_aead_setkey+0x2a/0xc0 crypto/aead.c:62 aead_setkey+0xc/0x10 crypto/algif_aead.c:526 alg_setkey crypto/af_alg.c:223 [inline] alg_setsockopt+0xfe/0x130 crypto/af_alg.c:256 __sys_setsockopt+0x6d/0xd0 net/socket.c:1902 __do_sys_setsockopt net/socket.c:1913 [inline] __se_sys_setsockopt net/socket.c:1910 [inline] __x64_sys_setsockopt+0x1f/0x30 net/socket.c:1910 do_syscall_64+0x4a/0x180 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe
Fixes: e236d4a89a2f ("[CRYPTO] authenc: Move enckeylen into key itself") Cc: stable@vger.kernel.org # v2.6.25+ Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- crypto/authenc.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
--- a/crypto/authenc.c +++ b/crypto/authenc.c @@ -58,14 +58,22 @@ int crypto_authenc_extractkeys(struct cr return -EINVAL; if (rta->rta_type != CRYPTO_AUTHENC_KEYA_PARAM) return -EINVAL; - if (RTA_PAYLOAD(rta) < sizeof(*param)) + + /* + * RTA_OK() didn't align the rtattr's payload when validating that it + * fits in the buffer. Yet, the keys should start on the next 4-byte + * aligned boundary. To avoid confusion, require that the rtattr + * payload be exactly the param struct, which has a 4-byte aligned size. + */ + if (RTA_PAYLOAD(rta) != sizeof(*param)) return -EINVAL; + BUILD_BUG_ON(sizeof(*param) % RTA_ALIGNTO);
param = RTA_DATA(rta); keys->enckeylen = be32_to_cpu(param->enckeylen);
- key += RTA_ALIGN(rta->rta_len); - keylen -= RTA_ALIGN(rta->rta_len); + key += rta->rta_len; + keylen -= rta->rta_len;
if (keylen < keys->enckeylen) return -EINVAL;