medium CVSS 5.5

CVE-2021-47365·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: afs: Fix page leak There's a loop in afs_extend_writeback() that adds extra pages to a write we want to make to improve the efficiency of the writeback by making it larger. This loop stops, however, if we hit a page we can't write back from immediately, but it doesn't get rid of the page ref we speculatively acquired. This was caused by the removal of the cleanup loop when the code switched from using find_get_pages_contig() to xarray scanning as the latter only gets a single page at a time, not a batch. Fix this by putting the page on a ref on an early break from the loop. Unfortunately, we can't just add that page to the pagevec we're employing as we'll go through that and add those pages to the RPC call. This was found by the generic/074 test. It leaks ~4GiB of RAM each time it is run - which can be observed with "top".

Severity: medium
Software: Kernel
Fixed in: 5.14.9
Published: 2024-05-21

Affected versions

From: 5.13

Until: 5.14.9

Fixed in: 5.14.9

How to fix this CVE

Update your Linux kernel to version 5.14.9 or later to resolve a memory leak in the AFS writeback mechanism. Systems running kernel versions 5.13 through 5.14.8 should prioritize this patch, as the vulnerability causes unreferenced memory pages to accumulate during file write operations, potentially exhausting available RAM over time.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

Check your current kernel version: uname -r
Verify if AFS (Andrew File System) is enabled: grep -i afs /boot/config-$(uname -r)
Monitor memory growth during file write operations on AFS-mounted filesystems using: watch -n 1 'free -h && ps aux | grep -E "write|afs"'
Confirm the patched kernel is running after update: uname -r | grep -E '5.14.9|5.15|5.16|5.17|5.18|5.19|6.'

FAQ

What is CVE-2021-47365?

CVE-2021-47365 is a kernel memory leak affecting AFS (Andrew File System) writeback operations. When the kernel attempts to optimize write performance by batching pages together, it fails to properly release page references under certain conditions, causing memory to remain allocated indefinitely.

Is CVE-2021-47365 being actively exploited?

No, this vulnerability is not listed in CISA's known exploited vulnerabilities catalog and no public exploits are available. However, it can cause significant system degradation through resource exhaustion.

What versions of Kernel are affected by CVE-2021-47365?

Linux kernel versions 5.13 through 5.14.8 are vulnerable. The fix was introduced in kernel 5.14.9 and all subsequent versions.

How do I check if my server is vulnerable to CVE-2021-47365?

Run `uname -r` and compare your kernel version against 5.14.9. If your version is between 5.13 and 5.14.8, you are vulnerable. Additionally verify AFS is used: `grep afs /proc/filesystems`.

Does Defensia detect CVE-2021-47365?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server running a vulnerable version, CVE-2021-47365 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2026-63994CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.

CVE-2026-64025CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: bpf, skmsg: fix verdict sk_data_ready racing with ktls rx sk_psock_strp_data_ready() already checks tls_sw_has_ctx_rx() and defers to psock->saved_data_ready when a TLS RX context is present, avoiding a conflict with the TLS strparser's ownership of the receive queue (commit e91de6afa81c, "bpf: Fix running sk_skb program types with ktls"). sk_psock_verdict_data_ready() has no equivalent guard. When a socket is inserted into a sockmap (BPF_SK_SKB_VERDICT) before TLS RX is configured, tls_sw_strparser_arm() saves sk_psock_verdict_data_ready as rx_ctx->saved_data_ready. On data arrival: tls_data_ready -> tls_strp_data_ready -> tls_rx_msg_ready -> saved_data_ready() = sk_psock_verdict_data_ready() -> tcp_read_skb() drains sk_receive_queue via __skb_unlink() without calling tcp_eat_skb(), so copied_seq is not advanced. tls_strp_msg_load() then finds tcp_inq() >= full_len (stale), calls tcp_recv_skb() on the now-empty queue, hits WARN_ON_ONCE(!first), and returns with rx_ctx->strp.anchor.frag_list pointing at a psock-owned (potentially freed) skb. tls_decrypt_sg() subsequently walks that frag_list: use-after-free. Apply the same fix as sk_psock_strp_data_ready(): if a TLS RX context is present, call psock->saved_data_ready (sock_def_readable) to wake recv() waiters and return immediately, leaving the receive queue untouched. TLS retains sole ownership of the queue and decrypts the record normally through tls_sw_recvmsg().

CVE-2026-100075CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: RDMA/srpt: Fix srpt_alloc_rw_ctxs() unwind counters When srpt_alloc_rw_ctxs() fails partway through a multi-buffer indirect descriptor, the unwind path destroys RDMA contexts but leaves stale n_rw_ctx and n_rdma values (and a dangling rw_ctxs pointer). Later sq_wr_avail accounting in srpt_queue_response() or srpt_write_pending() can then subtract the wrong number of send queue credits. Reset the counters and clear rw_ctxs after freeing the heap allocation before returning an error.

CVE-2026-64000CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: hsr: fix potential OOB access in supervision frame handling Ensure the entire TLV header is linearized before access by adding sizeof(struct hsr_sup_tlv) to the pskb_may_pull() calls. Without this, a truncated frame could cause an out-of-bounds access.

CVE-2026-64439CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: crypto: krb5 - filter out async aead implementations at alloc krb5_aead_encrypt(), krb5_aead_decrypt() in rfc3961_simplified.c and rfc8009_encrypt(), rfc8009_decrypt() in rfc8009_aes2.c set a NULL completion callback and treat any negative return from crypto_aead_{encrypt,decrypt}() as terminal, falling through to kfree_sensitive(buffer). When the encrypt_name resolves to an async AEAD instance the request returns -EINPROGRESS, the buffer is freed while the backend's worker still holds a pointer, and the worker dereferences the freed slab on completion. KASAN report under UML+SLUB with a synthetic async aead backend bound to krb5->encrypt_name: BUG: KASAN: slab-use-after-free in t5_stub_complete+0x7d/0xc7 The helpers were written synchronously, so filter the async instances out at allocation time instead of plumbing crypto_wait_req() through every call site. Reachable via net/rxrpc/rxgk.c, fs/afs/cm_security.c and net/ceph/crypto.c on systems with an async AEAD provider bound to the krb5 enctype name.

References

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