CVE-2026-90049 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
net: skbuff: don't skb_tx_error() the source skb in skb_zerocopy()
skb_zerocopy() copies frags from @from into @to. On an skb_orphan_frags() failure it calls skb_tx_error(@from), a destructive operation on the source skb the copy helper does not own. That completes @from's zerocopy uarg and clears SKBFL_ALL_ZEROCOPY, including the SKBFL_SHARED_FRAG page-ownership marker.
Both callers already report the failure on their own drop path. nfnetlink_queue does it at nla_put_failure, and Open vSwitch does it in the flow-miss drop arm of ovs_dp_process_packet(), so nothing is lost by dropping it here.
On Open vSwitch's OVS_ACTION_ATTR_USERSPACE path the skb is not freed on this error: do_execute_actions() ignores output_userspace()'s return value and, unless the upcall was the last action, keeps forwarding the same skb through the flow's remaining actions. The uarg is completed while that skb is still in flight, telling the producer its buffers are free, and SKBFL_SHARED_FRAG is cleared on an skb the rest of the stack still handles. That flag is what makes esp_input() call skb_cow_data() instead of decrypting in place, so a later local ESP delivery can decrypt over frags the skb does not own privately.
Leave error reporting to the callers.
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel vulnerability identified involves a critical logic flaw within the network subsystem's zero-copy packet handling mechanism, specifically located in the skbuff implementation of the function skb_zerocopy(). This routine is designed to copy fragment data from a source socket buffer, referred to as from, into a destination buffer, to. The core issue arises when the internal helper function skb_orphan_frags() fails during this operation. In such failure scenarios, the original implementation incorrectly invoked skb_tx_error() on the source skb. This action is fundamentally flawed because it constitutes a destructive modification of an object that the copy helper does not own or control exclusively. By calling this error handling routine, the code inadvertently completes the zero-copy user argument associated with the source buffer and clears critical flags such as SKBFL_ALL_ZEROCOPY. Most dangerously, it also clears the SKBFL_SHARED_FRAG page-ownership marker on a packet that remains in active use by other parts of the network stack.
This improper flag clearing leads to severe operational impacts related to memory safety and data integrity, particularly within Open vSwitch environments utilizing the OVS_ACTION_ATTR_USERSPACE path. When an error occurs during zero-copy operations in this context, the source socket buffer is not immediately freed because the do_execute_actions() function ignores the return value of output_userspace(). Consequently, unless the upcall was the final action, the system continues to forward the same skb through remaining flow actions while its internal state has been corrupted. The premature completion of the user argument signals to the producer that buffers are free for reuse, even though the kernel stack is still actively processing them. This race condition creates a scenario where shared fragments may be reclaimed or modified by other processes before the current packet handling sequence completes.
The security implications are particularly acute regarding IPsec ESP input operations. The SKBFL_SHARED_FRAG flag serves as a crucial indicator that dictates whether esp_input() should call skb_cow_data to ensure data integrity before processing, rather than attempting decryption in place. When this flag is incorrectly cleared due to the aforementioned error handling bug, subsequent local ESP delivery attempts may proceed with decrypting over fragments that are no longer exclusively owned by the socket buffer. This can lead to memory corruption vulnerabilities where decrypted plaintext is written into shared or potentially freed memory regions. Such conditions open the door for potential exploitation vectors including arbitrary code execution or denial of service through kernel panic caused by invalid memory access patterns during cryptographic operations.
From a classification perspective, this vulnerability aligns with CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization, as it involves race conditions between packet processing and buffer management logic. It also relates to CWE-416 Use After Free, given the risk of accessing memory that has been marked for reuse or release while still in flight within the network stack. In terms of MITRE ATT&CK mapping, this type of kernel-level state corruption can facilitate lateral movement or privilege escalation if an attacker can trigger the specific zero-copy failure path repeatedly to destabilize the system or corrupt critical networking structures. The flaw represents a classic case of improper error handling leading to inconsistent object states that violate memory safety invariants.
The resolution involves removing the erroneous call to skb_tx_error() from within skb_zerocopy(). Instead, responsibility for reporting and handling these errors is delegated back to the specific callers who initiated the zero-copy operation. This architectural correction ensures that nfnetlink_queue can properly handle failures at its nla_put_failure point, while Open vSwitch manages error conditions in the flow-miss drop arm of ovs_dp_process_packet(). By leaving error reporting to the callers, the patch prevents premature completion of user arguments and preserves critical ownership flags like SKBFL_SHARED_FRAG. This approach maintains the integrity of shared fragment references throughout their lifecycle, ensuring that cryptographic operations and other sensitive packet processing steps occur only when memory ownership is correctly established and stable.