{"id":"CVE-2021-47013","state":"PUBLISHED","title":"net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send\n\nIn emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..).\nIf some error happens in emac_tx_fill_tpd(), the skb will be freed via\ndev_kfree_skb(skb) in error branch of emac_tx_fill_tpd().\nBut the freed skb is still used via skb->len by netdev_sent_queue(,skb->len).\n\nAs i observed that emac_tx_fill_tpd() haven't modified the value of skb->len,\nthus my patch assigns skb->len to 'len' before the possible free and\nuse 'len' instead of skb->len later.","publishedAt":"2024-02-28T08:13:30.905Z","updatedAt":"2026-08-05T08:45:34.504Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"c7f75d11fe72913d2619f97b2334b083cd7bb955","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"dc1b438a35773d030be0ee80d9c635c3e558a322","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"16d8c44be52e3650917736d45f5904384a9da834","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"55fcdd1258faaecca74b91b88cc0921f9edd775d","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"9dc373f74097edd0e35f3393d6248eda8d1ba99d","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"8c06f34785068b87e2b560534c77c163d6c6dca7","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"e407495ba6788a67d1bd41714158c079e340879b","versionType":"git"},{"version":"b9b17debc69d27cd55e21ee51a5ba7fc50a426cf","status":"affected","lessThan":"6d72e7c767acbbdd44ebc7d89c6690b405b32b57","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ethernet/qualcomm/emac/emac-mac.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.9","versionType":"semver"},{"version":"4.9.269","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.233","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.191","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.119","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.37","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.11.21","status":"unaffected","lessThanOrEqual":"5.11.*","versionType":"semver"},{"version":"5.12.4","status":"unaffected","lessThanOrEqual":"5.12.*","versionType":"semver"},{"version":"5.13","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ethernet/qualcomm/emac/emac-mac.c"]}],"references":["https://git.kernel.org/stable/c/c7f75d11fe72913d2619f97b2334b083cd7bb955","https://git.kernel.org/stable/c/dc1b438a35773d030be0ee80d9c635c3e558a322","https://git.kernel.org/stable/c/16d8c44be52e3650917736d45f5904384a9da834","https://git.kernel.org/stable/c/55fcdd1258faaecca74b91b88cc0921f9edd775d","https://git.kernel.org/stable/c/9dc373f74097edd0e35f3393d6248eda8d1ba99d","https://git.kernel.org/stable/c/8c06f34785068b87e2b560534c77c163d6c6dca7","https://git.kernel.org/stable/c/e407495ba6788a67d1bd41714158c079e340879b","https://git.kernel.org/stable/c/6d72e7c767acbbdd44ebc7d89c6690b405b32b57"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:19.404Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/47xxx/CVE-2021-47013.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47013","state":"PUBLISHED","datePublished":"2024-02-28T08:13:30.905Z","dateUpdated":"2026-08-05T08:45:34.504Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-02-27T18:42:55.953Z"},"containers":{"cna":{"title":"net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send\n\nIn emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..).\nIf some error happens in emac_tx_fill_tpd(), the skb will be freed via\ndev_kfree_skb(skb) in error branch of emac_tx_fill_tpd().\nBut the freed skb is still used via skb->len by netdev_sent_queue(,skb->len).\n\nAs i observed that emac_tx_fill_tpd() haven't modified the value of skb->len,\nthus my patch assigns skb->len to 'len' before the possible free and\nuse 'len' instead of skb->len 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- The bug is in the Qualcomm EMAC ndo_start_xmit path (emac_start_xmit → emac_mac_tx_buf_send), used on network-facing FSM9900/QDF platforms; a remote peer can drive TX via ARP/ICMP/TCP replies or forwarded traffic through this NIC, matching other ethernet TX CVEs.\nAC:L - An attacker can flood traffic to raise DMA/swiotlb pressure until dma_mapping_error() hits; once that failure occurs the UAF of skb->len is deterministic, as scored for similar dma_mapping_error TX bugs (e.g. CVE-2024-50170).\nPR:N - No authentication or capability check sits on this path—unauthenticated remote traffic that elicits kernel TX, or an unprivileged local socket send, reaches emac_mac_tx_buf_send.\nUI:N - No victim action is required; ordinary network traffic or local sends autonomously exercise the transmit path.\nS:U - The UAF corrupts/abuses kernel skb and BQL state within the same host security authority; the TX ring produce index is rolled back on the error path so no IOMMU/DMA boundary is crossed.\nC:H - This is a use-after-free of an sk_buff: after dev_kfree_skb() the freed object can be reclaimed via heap spray, and UAF of skb metadata is treated as enabling arbitrary kernel memory disclosure primitives.\nI:H - Use-after-free of the skb enables heap reuse/type confusion and attacker-controlled BQL byte accounting via the post-free skb->len read, which is leverageable for memory corruption and control-flow impact.\nA:H - Dereferencing the freed skb can oops if the object is poisoned or unmapped, and the post-free netdev_sent_queue() permanently inflates BQL without a matching completion, enabling TX queue stall or kernel 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