fs: Prevent file descriptor table allocations exceeding INT_MAX

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Summary

CVECVE-2025-39756
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-09-11 17:15:39 UTC
Updated2026-05-12 13:17:09 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: fs: Prevent file descriptor table allocations exceeding INT_MAX When sysctl_nr_open is set to a very high value (for example, 1073741816 as set by systemd), processes attempting to use file descriptors near the limit can trigger massive memory allocation attempts that exceed INT_MAX, resulting in a WARNING in mm/slub.c: WARNING: CPU: 0 PID: 44 at mm/slub.c:5027 __kvmalloc_node_noprof+0x21a/0x288 This happens because kvmalloc_array() and kvmalloc() check if the requested size exceeds INT_MAX and emit a warning when the allocation is not flagged with __GFP_NOWARN. Specifically, when nr_open is set to 1073741816 (0x3ffffff8) and a process calls dup2(oldfd, 1073741880), the kernel attempts to allocate: - File descriptor array: 1073741880 * 8 bytes = 8,589,935,040 bytes - Multiple bitmaps: ~400MB - Total allocation size: > 8GB (exceeding INT_MAX = 2,147,483,647) Reproducer: 1. Set /proc/sys/fs/nr_open to 1073741816: # echo 1073741816 > /proc/sys/fs/nr_open 2. Run a program that uses a high file descriptor: #include <unistd.h> #include <sys/resource.h> int main() { struct rlimit rlim = {1073741824, 1073741824}; setrlimit(RLIMIT_NOFILE, &rlim); dup2(2, 1073741880); // Triggers the warning return 0; } 3. Observe WARNING in dmesg at mm/slub.c:5027 systemd commit a8b627a introduced automatic bumping of fs.nr_open to the maximum possible value. The rationale was that systems with memory control groups (memcg) no longer need separate file descriptor limits since memory is properly accounted. However, this change overlooked that: 1. The kernel's allocation functions still enforce INT_MAX as a maximum size regardless of memcg accounting 2. Programs and tests that legitimately test file descriptor limits can inadvertently trigger massive allocations 3. The resulting allocations (>8GB) are impractical and will always fail systemd's algorithm starts with INT_MAX and keeps halving the value until the kernel accepts it. On most systems, this results in nr_open being set to 1073741816 (0x3ffffff8), which is just under 1GB of file descriptors. While processes rarely use file descriptors near this limit in normal operation, certain selftests (like tools/testing/selftests/core/unshare_test.c) and programs that test file descriptor limits can trigger this issue. Fix this by adding a check in alloc_fdtable() to ensure the requested allocation size does not exceed INT_MAX. This causes the operation to fail with -EMFILE instead of triggering a kernel warning and avoids the impractical >8GB memory allocation request.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-401

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b b4159c5a90c03f8acd3de345a7f5fc63b0909818 git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b f95638a8f22eba307dceddf5aef9ae2326bbcf98 git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b 749528086620f8012b83ae032a80f6ffa80c45cd git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b 628fc28f42d979f36dbf75a6129ac7730e30c04e git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b 237e416eb62101f21b28c9e6e564d10efe1ecc6f git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b 9f61fa6a2a89a610120bc4e5d24379c667314b5c git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae git Not specified
CNA Linux Linux affected 9cfe015aa424b3c003baba3841a60dd9b5ad319b 04a2c4b4511d186b0fce685da21085a5d4acd370 git Not specified
CNA Linux Linux affected 2.6.25 Not specified
CNA Linux Linux unaffected 2.6.25 semver Not specified
CNA Linux Linux unaffected 5.4.297 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.241 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.190 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.149 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.103 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.43 6.12.* semver Not specified
CNA Linux Linux unaffected 6.15.11 6.15.* semver Not specified
CNA Linux Linux unaffected 6.16.2 6.16.* semver Not specified
CNA Linux Linux unaffected 6.17 * original_commit_for_fix Not specified
ADP Siemens SIMATIC CN 4100 affected V5.0 custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/237e416eb62101f21b28c9e6e564d10efe1ecc6f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/10/msg00008.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Mailing List, Third Party Advisory
git.kernel.org/stable/c/628fc28f42d979f36dbf75a6129ac7730e30c04e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-082556.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/04a2c4b4511d186b0fce685da21085a5d4acd370 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/9f61fa6a2a89a610120bc4e5d24379c667314b5c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-032379.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/f95638a8f22eba307dceddf5aef9ae2326bbcf98 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/749528086620f8012b83ae032a80f6ffa80c45cd 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/10/msg00007.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Mailing List, Third Party Advisory
git.kernel.org/stable/c/b4159c5a90c03f8acd3de345a7f5fc63b0909818 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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