{"id":"CVE-2025-39756","state":"PUBLISHED","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 <unistd.h>\n   #include <sys/resource.h>\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.","publishedAt":"2025-09-11T16:52:26.136Z","updatedAt":"2026-10-15T01:08:10.812Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"b4159c5a90c03f8acd3de345a7f5fc63b0909818","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"f95638a8f22eba307dceddf5aef9ae2326bbcf98","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"749528086620f8012b83ae032a80f6ffa80c45cd","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"628fc28f42d979f36dbf75a6129ac7730e30c04e","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"237e416eb62101f21b28c9e6e564d10efe1ecc6f","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"9f61fa6a2a89a610120bc4e5d24379c667314b5c","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"04a2c4b4511d186b0fce685da21085a5d4acd370","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/file.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.25","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.25","versionType":"semver"},{"version":"5.4.297","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.241","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.190","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.149","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.103","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.43","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.15.11","status":"unaffected","lessThanOrEqual":"6.15.*","versionType":"semver"},{"version":"6.16.2","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/file.c"]}],"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","https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html","https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-032379.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/39xxx/CVE-2025-39756.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-39756","state":"PUBLISHED","datePublished":"2025-09-11T16:52:26.136Z","dateUpdated":"2026-10-15T01:08:10.812Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T07:20:57.125Z"},"containers":{"cna":{"title":"fs: Prevent file descriptor table allocations exceeding INT_MAX","descriptions":[{"lang":"en","value":"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 <unistd.h>\n   #include <sys/resource.h>\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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"b4159c5a90c03f8acd3de345a7f5fc63b0909818","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"f95638a8f22eba307dceddf5aef9ae2326bbcf98","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"749528086620f8012b83ae032a80f6ffa80c45cd","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"628fc28f42d979f36dbf75a6129ac7730e30c04e","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"237e416eb62101f21b28c9e6e564d10efe1ecc6f","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"9f61fa6a2a89a610120bc4e5d24379c667314b5c","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae","versionType":"git"},{"version":"9cfe015aa424b3c003baba3841a60dd9b5ad319b","status":"affected","lessThan":"04a2c4b4511d186b0fce685da21085a5d4acd370","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/file.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.25","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.25","versionType":"semver"},{"version":"5.4.297","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.241","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.190","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.149","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.103","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.43","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.15.11","status":"unaffected","lessThanOrEqual":"6.15.*","versionType":"semver"},{"version":"6.16.2","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/file.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/b4159c5a90c03f8acd3de345a7f5fc63b0909818"},{"url":"https://git.kernel.org/stable/c/f95638a8f22eba307dceddf5aef9ae2326bbcf98"},{"url":"https://git.kernel.org/stable/c/749528086620f8012b83ae032a80f6ffa80c45cd"},{"url":"https://git.kernel.org/stable/c/628fc28f42d979f36dbf75a6129ac7730e30c04e"},{"url":"https://git.kernel.org/stable/c/237e416eb62101f21b28c9e6e564d10efe1ecc6f"},{"url":"https://git.kernel.org/stable/c/d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc"},{"url":"https://git.kernel.org/stable/c/9f61fa6a2a89a610120bc4e5d24379c667314b5c"},{"url":"https://git.kernel.org/stable/c/dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae"},{"url":"https://git.kernel.org/stable/c/04a2c4b4511d186b0fce685da21085a5d4acd370"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T21:35:39.094Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"5.4.297"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"5.10.241"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"5.15.190"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"6.1.149"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"6.6.103"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"6.12.43"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"6.15.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"6.16.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.25","versionEndExcluding":"6.17"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"a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