CVE-2025-39756
published 2025-09-11CVE-2025-39756: In the Linux kernel, the following vulnerability has been resolved: fs: Prevent file descriptor table allocations exceeding INT_MAX When sysctl_nr_open is set…
medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
In 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
#include
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 syste
Affected
38 ranges· showing 25
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | debian_linux | — | — |
| debian | linux | < linux 6.1.153-1 (bookworm) | linux 6.1.153-1 (bookworm) |
| debian | linux-6.1 | < linux 6.1.153-1 (bookworm) | linux 6.1.153-1 (bookworm) |
| linux | linux | — | — |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < b4159c5a90c03f8acd3de345a7f5fc63b0909818 | b4159c5a90c03f8acd3de345a7f5fc63b0909818 |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < f95638a8f22eba307dceddf5aef9ae2326bbcf98 | f95638a8f22eba307dceddf5aef9ae2326bbcf98 |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < 749528086620f8012b83ae032a80f6ffa80c45cd | 749528086620f8012b83ae032a80f6ffa80c45cd |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < 628fc28f42d979f36dbf75a6129ac7730e30c04e | 628fc28f42d979f36dbf75a6129ac7730e30c04e |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < 237e416eb62101f21b28c9e6e564d10efe1ecc6f | 237e416eb62101f21b28c9e6e564d10efe1ecc6f |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc | d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < 9f61fa6a2a89a610120bc4e5d24379c667314b5c | 9f61fa6a2a89a610120bc4e5d24379c667314b5c |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae | dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae |
| linux | linux | >= 9cfe015aa424b3c003baba3841a60dd9b5ad319b < 04a2c4b4511d186b0fce685da21085a5d4acd370 | 04a2c4b4511d186b0fce685da21085a5d4acd370 |
| linux | linux_kernel | >= 0 < 5.10.244-1 | 5.10.244-1 |
| linux | linux_kernel | >= 0 < 6.1.153-1 | 6.1.153-1 |
| linux | linux_kernel | >= 0 < 6.12.43-1 | 6.12.43-1 |
| linux | linux_kernel | >= 0 < 6.16.3-1 | 6.16.3-1 |
| linux | linux_kernel | >= 0 < 5.15.0-163.173 | 5.15.0-163.173 |
| linux | linux_kernel | >= 0 < 6.8.0-100.100 | 6.8.0-100.100 |
| linux | linux_kernel | >= 2.6.25 < 5.4.297 | 5.4.297 |
| linux | linux_kernel | >= 5.11 < 5.15.190 | 5.15.190 |
| linux | linux_kernel | >= 5.16 < 6.1.149 | 6.1.149 |
| linux | linux_kernel | >= 5.5 < 5.10.241 | 5.10.241 |
| linux | linux_kernel | >= 6.13 < 6.15.11 | 6.15.11 |
| linux | linux_kernel | >= 6.16 < 6.16.2 | 6.16.2 |
CVSS provenance
nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv5.5MEDIUM