{"id":"CVE-2025-39756","revision":"dae3c75b7fad47ee892e843a932bc6b0","records":[{"revision":"dae3c75b7fad47ee892e843a932bc6b0","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2025-39756","aliases":[],"title":"fs: Prevent file descriptor table allocations exceeding INT_MAX","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs: Prevent file descriptor table allocations exceeding INT_MAX\n\nWhen sysctl_nr_open is set to a very high value (for example, 1073741816\nas set by systemd), processes attempting to use file descriptors near\nthe limit can trigger massive memory allocation attempts that exceed\nINT_MAX, resulting in a WARNING in mm/slub.c:\n\n WARNING: CPU: 0 PID: 44 at mm/slub.c:5027 __kvmalloc_node_noprof+0x21a/0x288\n\nThis happens because kvmalloc_array() and kvmalloc() check if the\nrequested size exceeds INT_MAX and emit a warning when the allocation is\nnot flagged with __GFP_NOWARN.\n\nSpecifically, when nr_open is set to 1073741816 (0x3ffffff8) and a\nprocess calls dup2(oldfd, 1073741880), the kernel attempts to allocate:\n- File descriptor array: 1073741880 * 8 bytes = 8,589,935,040 bytes\n- Multiple bitmaps: ~400MB\n- Total allocation size: > 8GB (exceeding INT_MAX = 2,147,483,647)\n\nReproducer:\n1. Set /proc/sys/fs/nr_open to 1073741816:\n # echo 1073741816 > /proc/sys/fs/nr_open\n\n2. Run a program that uses a high file descriptor:\n #include \n #include \n\n int main() {\n struct rlimit rlim = {1073741824, 1073741824};\n setrlimit(RLIMIT_NOFILE, &rlim);\n dup2(2, 1073741880); // Triggers the warning\n return 0;\n }\n\n3. Observe WARNING in dmesg at mm/slub.c:5027\n\nsystemd commit a8b627a introduced automatic bumping of fs.nr_open to the\nmaximum possible value. The rationale was that systems with memory\ncontrol groups (memcg) no longer need separate file descriptor limits\nsince memory is properly accounted. However, this change overlooked\nthat:\n\n1. The kernel's allocation functions still enforce INT_MAX as a maximum\n size regardless of memcg accounting\n2. Programs and tests that legitimately test file descriptor limits can\n inadvertently trigger massive allocations\n3. The resulting allocations (>8GB) are impractical and will always fail\n\nsystemd's algorithm starts with INT_MAX and keeps halving the value\nuntil the kernel accepts it. On most systems, this results in nr_open\nbeing set to 1073741816 (0x3ffffff8), which is just under 1GB of file\ndescriptors.\n\nWhile processes rarely use file descriptors near this limit in normal\noperation, certain selftests (like\ntools/testing/selftests/core/unshare_test.c) and programs that test file\ndescriptor limits can trigger this issue.\n\nFix this by adding a check in alloc_fdtable() to ensure the requested\nallocation size does not exceed INT_MAX. This causes the operation to\nfail with -EMFILE instead of triggering a kernel warning and avoids the\nimpractical >8GB memory allocation request.","state":0,"publishedAt":"2025-09-11T16:52:26.136+00:00","modifiedAt":"2026-10-15T01:08:10.812+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/file.c\"\n ],\n \"versions\": [\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"b4159c5a90c03f8acd3de345a7f5fc63b0909818\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"f95638a8f22eba307dceddf5aef9ae2326bbcf98\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"749528086620f8012b83ae032a80f6ffa80c45cd\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"628fc28f42d979f36dbf75a6129ac7730e30c04e\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"237e416eb62101f21b28c9e6e564d10efe1ecc6f\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"9f61fa6a2a89a610120bc4e5d24379c667314b5c\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"9cfe015aa424b3c003baba3841a60dd9b5ad319b\",\n \"lessThan\": \"04a2c4b4511d186b0fce685da21085a5d4acd370\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/file.c\"\n ],\n \"versions\": [\n {\n \"version\": \"2.6.25\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"2.6.25\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.4.297\",\n \"lessThanOrEqual\": \"5.4.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.10.241\",\n \"lessThanOrEqual\": \"5.10.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.190\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.149\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.103\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.43\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.15.11\",\n \"lessThanOrEqual\": \"6.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.16.2\",\n \"lessThanOrEqual\": \"6.16.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.17\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/b4159c5a90c03f8acd3de345a7f5fc63b0909818","https://git.kernel.org/stable/c/f95638a8f22eba307dceddf5aef9ae2326bbcf98","https://git.kernel.org/stable/c/749528086620f8012b83ae032a80f6ffa80c45cd","https://git.kernel.org/stable/c/628fc28f42d979f36dbf75a6129ac7730e30c04e","https://git.kernel.org/stable/c/237e416eb62101f21b28c9e6e564d10efe1ecc6f","https://git.kernel.org/stable/c/d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc","https://git.kernel.org/stable/c/9f61fa6a2a89a610120bc4e5d24379c667314b5c","https://git.kernel.org/stable/c/dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae","https://git.kernel.org/stable/c/04a2c4b4511d186b0fce685da21085a5d4acd370"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-39756","license":"CVE Program Terms of Use","key":"cve-program:CVE-2025-39756","identifiers":["CVE-2025-39756"]},"retained":false,"historicalAffected":[]}],"coverage":[]}