{"id":"CVE-2024-42243","url":"https://www.cyber-defence.io/tools/cve/CVE-2024-42243","generatedAt":"2026-10-28T02:13:48.813Z","title":"In the Linux kernel, the following vulnerability has been resolved: mm/filemap: make MAX_PAGECACHE_ORDER acceptable to xarray Patch series \"mm/filemap: Limit page cache size to that supported by xarray\", v2.","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/filemap: make MAX_PAGECACHE_ORDER acceptable to xarray\n\nPatch series \"mm/filemap: Limit page cache size to that supported by\nxarray\", v2.\n\nCurrently, xarray can't support arbitrary page cache size.  More details\ncan be found from the WARN_ON() statement in xas_split_alloc().  In our\ntest whose code is attached below, we hit the WARN_ON() on ARM64 system\nwhere the base page size is 64KB and huge page size is 512MB.  The issue\nwas reported long time ago and some discussions on it can be found here\n[1].\n\n[1] https://www.spinics.net/lists/linux-xfs/msg75404.html\n\nIn order to fix the issue, we need to adjust MAX_PAGECACHE_ORDER to one\nsupported by xarray and avoid PMD-sized page cache if needed.  The code\nchanges are suggested by David Hildenbrand.\n\nPATCH[1] adjusts MAX_PAGECACHE_ORDER to that supported by xarray\nPATCH[2-3] avoids PMD-sized page cache in the synchronous readahead path\nPATCH[4] avoids PMD-sized page cache for shmem files if needed\n\nTest program\n============\n# cat test.c\n#define _GNU_SOURCE\n#include <stdio.h>\n#include <stdlib.h>\n#include <unistd.h>\n#include <string.h>\n#include <fcntl.h>\n#include <errno.h>\n#include <sys/syscall.h>\n#include <sys/mman.h>\n\n#define TEST_XFS_FILENAME\t\"/tmp/data\"\n#define TEST_SHMEM_FILENAME\t\"/dev/shm/data\"\n#define TEST_MEM_SIZE\t\t0x20000000\n\nint main(int argc, char **argv)\n{\n\tconst char *filename;\n\tint fd = 0;\n\tvoid *buf = (void *)-1, *p;\n\tint pgsize = getpagesize();\n\tint ret;\n\n\tif (pgsize != 0x10000) {\n\t\tfprintf(stderr, \"64KB base page size is required\\n\");\n\t\treturn -EPERM;\n\t}\n\n\tsystem(\"echo force > /sys/kernel/mm/transparent_hugepage/shmem_enabled\");\n\tsystem(\"rm -fr /tmp/data\");\n\tsystem(\"rm -fr /dev/shm/data\");\n\tsystem(\"echo 1 > /proc/sys/vm/drop_caches\");\n\n\t/* Open xfs or shmem file */\n\tfilename = TEST_XFS_FILENAME;\n\tif (argc > 1 && !strcmp(argv[1], \"shmem\"))\n\t\tfilename = TEST_SHMEM_FILENAME;\n\n\tfd = open(filename, O_CREAT | O_RDWR | O_TRUNC);\n\tif (fd < 0) {\n\t\tfprintf(stderr, \"Unable to open <%s>\\n\", filename);\n\t\treturn -EIO;\n\t}\n\n\t/* Extend file size */\n\tret = ftruncate(fd, TEST_MEM_SIZE);\n\tif (ret) {\n\t\tfprintf(stderr, \"Error %d to ftruncate()\\n\", ret);\n\t\tgoto cleanup;\n\t}\n\n\t/* Create VMA */\n\tbuf = mmap(NULL, TEST_MEM_SIZE,\n\t\t   PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);\n\tif (buf == (void *)-1) {\n\t\tfprintf(stderr, \"Unable to mmap <%s>\\n\", filename);\n\t\tgoto cleanup;\n\t}\n\n\tfprintf(stdout, \"mapped buffer at 0x%p\\n\", buf);\n\tret = madvise(buf, TEST_MEM_SIZE, MADV_HUGEPAGE);\n        if (ret) {\n\t\tfprintf(stderr, \"Unable to madvise(MADV_HUGEPAGE)\\n\");\n\t\tgoto cleanup;\n\t}\n\n\t/* Populate VMA */\n\tret = madvise(buf, TEST_MEM_SIZE, MADV_POPULATE_WRITE);\n\tif (ret) {\n\t\tfprintf(stderr, \"Error %d to madvise(MADV_POPULATE_WRITE)\\n\", ret);\n\t\tgoto cleanup;\n\t}\n\n\t/* Punch the file to enforce xarray split */\n\tret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,\n        \t\tTEST_MEM_SIZE - pgsize, pgsize);\n\tif (ret)\n\t\tfprintf(stderr, \"Error %d to fallocate()\\n\", ret);\n\ncleanup:\n\tif (buf != (void *)-1)\n\t\tmunmap(buf, TEST_MEM_SIZE);\n\tif (fd > 0)\n\t\tclose(fd);\n\n\treturn 0;\n}\n\n# gcc test.c -o test\n# cat /proc/1/smaps | grep KernelPageSize | head -n 1\nKernelPageSize:       64 kB\n# ./test shmem\n   :\n------------[ cut here ]------------\nWARNING: CPU: 17 PID: 5253 at lib/xarray.c:1025 xas_split_alloc+0xf8/0x128\nModules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib  \\\nnft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct    \\\nnft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4    \\\nip_set nf_tables rfkill nfnetlink vfat fat virtio_balloon          \\\ndrm fuse xfs libcrc32c crct10dif_ce ghash_ce sha2_ce sha256_arm64  \\\nvirtio_net sha1_ce net_failover failover virtio_console virtio_blk \\\ndimlib virtio_mmio\nCPU: 17 PID: 5253 Comm: test Kdump: loaded Tainted: G W 6.10.0-rc5-gavin+ #12\nHardware name: QEMU KVM Virtual Machine, BIOS edk2-20240524-1.el9 05/24/2024\npstate: 83400005 (Nzcv daif +PAN -UAO +TC\n---truncated---","published":"2024-08-07T16:15:47.000Z","lastModified":"2026-06-17T07:49:05.000Z","status":"Analyzed","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":5.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"},"cwe":[],"affected":["linux/linux kernel"],"epss":{"score":0.00211,"percentile":0.11339,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.21%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/099d90642a711caae377f53309abfe27e8724a8b","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/333c5539a31f48828456aa9997ec2808f06a699a","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a0c42ddd0969fdc760a85e20e267776028a7ca4e","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2024-42243","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}