{"cve":"CVE-2021-47375","nvd":{"published":"2024-05-21T15:15:23.290","modified":"2026-06-17T04:17:19.560","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nblktrace: Fix uaf in blk_trace access after removing by sysfs\n\nThere is an use-after-free problem triggered by following process:\n\n      P1(sda)\t\t\t\tP2(sdb)\n\t\t\techo 0 > /sys/block/sdb/trace/enable\n\t\t\t  blk_trace_remove_queue\n\t\t\t    synchronize_rcu\n\t\t\t    blk_trace_free\n\t\t\t      relay_close\nrcu_read_lock\n__blk_add_trace\n  trace_note_tsk\n  (Iterate running_trace_list)\n\t\t\t        relay_close_buf\n\t\t\t\t  relay_destroy_buf\n\t\t\t\t    kfree(buf)\n    trace_note(sdb's bt)\n      relay_reserve\n        buf->offset <- nullptr deference (use-after-free) !!!\nrcu_read_unlock\n\n[  502.714379] BUG: kernel NULL pointer dereference, address:\n0000000000000010\n[  502.715260] #PF: supervisor read access in kernel mode\n[  502.715903] #PF: error_code(0x0000) - not-present page\n[  502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0\n[  502.717252] Oops: 0000 [#1] SMP\n[  502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360\n[  502.732872] Call Trace:\n[  502.733193]  __blk_add_trace.cold+0x137/0x1a3\n[  502.733734]  blk_add_trace_rq+0x7b/0xd0\n[  502.734207]  blk_add_trace_rq_issue+0x54/0xa0\n[  502.734755]  blk_mq_start_request+0xde/0x1b0\n[  502.735287]  scsi_queue_rq+0x528/0x1140\n...\n[  502.742704]  sg_new_write.isra.0+0x16e/0x3e0\n[  502.747501]  sg_ioctl+0x466/0x1100\n\nReproduce method:\n  ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])\n  ioctl(/dev/sda, BLKTRACESTART)\n  ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])\n  ioctl(/dev/sdb, BLKTRACESTART)\n\n  echo 0 > /sys/block/sdb/trace/enable &\n  // Add delay(mdelay/msleep) before kernel enters blk_trace_free()\n\n  ioctl$SG_IO(/dev/sda, SG_IO, ...)\n  // Enters trace_note_tsk() after blk_trace_free() returned\n  // Use mdelay in rcu region rather than msleep(which may schedule out)\n\nRemove blk_trace from running_list before calling blk_trace_free() by\nsysfs if blk_trace is at Blktrace_running state.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","score":6.2},"cwes":["CWE-416"],"references":["https://git.kernel.org/stable/c/3815fe7371d2411ce164281cef40d9fc7b323dee","https://git.kernel.org/stable/c/488da313edf3abea7f7733efe011c96b23740ab5","https://git.kernel.org/stable/c/5afedf670caf30a2b5a52da96eb7eac7dee6a9c9","https://git.kernel.org/stable/c/677e362ba807f3aafe6f405c07e0b37244da5222","https://git.kernel.org/stable/c/a5f8e86192612d0183047448d8bbe7918b3f1a26"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T21:50:30.954589733+00:00"},"epss":{"cve":"CVE-2021-47375","score":0.00254,"percentile":0.16928,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}