ghsa-7fhq-j7h5-cjxg
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
tcp: Correct signedness in skb remaining space calculation
Syzkaller reported a bug 1 where sk->sk_forward_alloc can overflow.
When we send data, if an skb exists at the tail of the write queue, the kernel will attempt to append the new data to that skb. However, the code that checks for available space in the skb is flawed: ''' copy = size_goal - skb->len '''
The types of the variables involved are: ''' copy: ssize_t (s64 on 64-bit systems) size_goal: int skb->len: unsigned int '''
Due to C's type promotion rules, the signed size_goal is converted to an unsigned int to match skb->len before the subtraction. The result is an unsigned int.
When this unsigned int result is then assigned to the s64 copy variable, it is zero-extended, preserving its non-negative value. Consequently, copy is always >= 0.
Assume we are sending 2GB of data and size_goal has been adjusted to a value smaller than skb->len. The subtraction will result in copy holding a very large positive integer. In the subsequent logic, this large value is used to update sk->sk_forward_alloc, which can easily cause it to overflow.
The syzkaller reproducer uses TCP_REPAIR to reliably create this condition. However, this can also occur in real-world scenarios. The tcp_bound_to_half_wnd() function can also reduce size_goal to a small value. This would cause the subsequent tcp_wmem_schedule() to set sk->sk_forward_alloc to a value close to INT_MAX. Further memory allocation requests would then cause sk_forward_alloc to wrap around and become negative.
{
"affected": [],
"aliases": [
"CVE-2025-38463"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-07-25T16:15:32Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Correct signedness in skb remaining space calculation\n\nSyzkaller reported a bug [1] where sk-\u003esk_forward_alloc can overflow.\n\nWhen we send data, if an skb exists at the tail of the write queue, the\nkernel will attempt to append the new data to that skb. However, the code\nthat checks for available space in the skb is flawed:\n\u0027\u0027\u0027\ncopy = size_goal - skb-\u003elen\n\u0027\u0027\u0027\n\nThe types of the variables involved are:\n\u0027\u0027\u0027\ncopy: ssize_t (s64 on 64-bit systems)\nsize_goal: int\nskb-\u003elen: unsigned int\n\u0027\u0027\u0027\n\nDue to C\u0027s type promotion rules, the signed size_goal is converted to an\nunsigned int to match skb-\u003elen before the subtraction. The result is an\nunsigned int.\n\nWhen this unsigned int result is then assigned to the s64 copy variable,\nit is zero-extended, preserving its non-negative value. Consequently, copy\nis always \u003e= 0.\n\nAssume we are sending 2GB of data and size_goal has been adjusted to a\nvalue smaller than skb-\u003elen. The subtraction will result in copy holding a\nvery large positive integer. In the subsequent logic, this large value is\nused to update sk-\u003esk_forward_alloc, which can easily cause it to overflow.\n\nThe syzkaller reproducer uses TCP_REPAIR to reliably create this\ncondition. However, this can also occur in real-world scenarios. The\ntcp_bound_to_half_wnd() function can also reduce size_goal to a small\nvalue. This would cause the subsequent tcp_wmem_schedule() to set\nsk-\u003esk_forward_alloc to a value close to INT_MAX. Further memory\nallocation requests would then cause sk_forward_alloc to wrap around and\nbecome negative.\n\n[1]: https://syzkaller.appspot.com/bug?extid=de6565462ab540f50e47",
"id": "GHSA-7fhq-j7h5-cjxg",
"modified": "2025-07-25T18:30:40Z",
"published": "2025-07-25T18:30:40Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38463"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/62e6160cfb5514787bda833d466509edc38fde23"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/81373cd1d72d87c7d844d4454a526b8f53e72d00"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9f164fa6bb09fbcc60fa5c3ff551ce9eec1befd7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d3a5f2871adc0c61c61869f37f3e697d97f03d8c"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.