Linux KernelOperating system · Linux
CVE-2022-49093
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn the Linux kernel, the following vulnerability has been resolved: skbuff: fix coalescing for page_pool fragment recycling Fix a use-after-free when using page_pool with page fragments. We encountered this problem during normal RX in the hns3 driver: (1) Initially we have three descriptors in the RX queue. The first one allocates PAGE1 through page_pool, and the other two allocate one half of PAGE2 each. Page references look like this: RX_BD1 _______ PAGE1 RX_BD2 _______ PAGE2 RX_BD3 _________/ (2) Handle RX on the first descriptor. Allocate SKB1, eventually added to the receive queue by tcp_queue_rcv(). (3) Handle RX on the second descriptor. Allocate SKB2 and pass it to netif_receive_skb(): netif_receive_skb(SKB2) ip_rcv(SKB2) SKB3 = skb_clone(SKB2) SKB2 and SKB3 share a reference to PAGE2 through skb_shinfo()->dataref. The other ref to PAGE2 is still held by RX_BD3: SKB2 ---+- PAGE2 SKB3 __/ / RX_BD3 _________/ (3b) Now while handling TCP, coalesce SKB3 with SKB1: tcp_v4_rcv(SKB3) tcp_try_coalesce(to=SKB1, from=SKB3) // succeeds kfree_skb_partial(SKB3) skb_release_data(SKB3) // drops one dataref SKB1 _____ PAGE1 \____ SKB2 _____ PAGE2 / RX_BD3 _________/ In skb_try_coalesce(), __skb_frag_ref() takes a page reference to PAGE2, where it should instead have increased the page_pool frag reference, pp_frag_count. Without coalescing, when releasing both SKB2 and SKB3, a single reference to PAGE2 would be dropped. Now when releasing SKB1 and SKB2, two references to PAGE2 will be dropped, resulting in underflow. (3c) Drop SKB2: af_packet_rcv(SKB2) consume_skb(SKB2) skb_release_data(SKB2) // drops second dataref page_pool_return_skb_page(PAGE2) // drops one pp_frag_count SKB1 _____ PAGE1 \____ PAGE2 / RX_BD3 _________/ (4) Userspace calls recvmsg() Copies SKB1 and releases it. Since SKB3 was coalesced with SKB1, we release the SKB3 page as well: tcp_eat_recv_skb(SKB1) skb_release_data(SKB1) page_pool_return_skb_page(PAGE1) page_pool_return_skb_page(PAGE2) // drops second pp_frag_count (5) PAGE2 is freed, but the third RX descriptor was still using it! In our case this causes IOMMU faults, but it would silently corrupt memory if the IOMMU was disabled. Change the logic that checks whether pp_recycle SKBs can be coalesced. We still reject differing pp_recycle between 'from' and 'to' SKBs, but in order to avoid the situation described above, we also reject coalescing when both 'from' and 'to' are pp_recycled and 'from' is cloned. The new logic allows coalescing a cloned pp_recycle SKB into a page refcounted one, because in this case the release (4) will drop the right reference, the one taken by skb_try_coalesce().
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisMemory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.
General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Linux KernelOperating system
>= 5.15, < 5.15.34>= 5.16, < 5.16.20>= 5.17, < 5.17.3= 5.18CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped5.15.345.16.205.17.3
5.15.34 / 5.16.20 / 5.17.3 / latest 5.18.x or later stable branch
- 1. Identify the currently running kernel version using 'uname -r' or 'cat /proc/version'
- 2. If running kernel 5.15.x, upgrade to kernel 5.15.34 or later
- 3. If running kernel 5.16.x, upgrade to kernel 5.16.20 or later
- 4. If running kernel 5.17.x, upgrade to kernel 5.17.3 or later
- 5. If running kernel 5.18.x, upgrade to the latest stable 5.18.x release that includes the fix, or migrate to a newer stable branch (e.g., 5.19 or later)
- 6. After upgrading, reboot the system to load the fixed kernel
- 7. Verify the fix is applied by checking the kernel version matches the fixed releases above
Generated from the published advisory — verify against the referenced sources before acting.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2022-49093 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2022-49093 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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