{
   "containers": {
      "cna": {
         "providerMetadata": {
            "orgId": "f4215fc3-5b6b-47ff-a258-f7189bd81038"
         },
         "descriptions": [
            {
               "lang": "en",
               "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nlocking/qrwlock: Fix ordering in queued_write_lock_slowpath()\n\nWhile this code is executed with the wait_lock held, a reader can\nacquire the lock without holding wait_lock.  The writer side loops\nchecking the value with the atomic_cond_read_acquire(), but only truly\nacquires the lock when the compare-and-exchange is completed\nsuccessfully which isn’t ordered. This exposes the window between the\nacquire and the cmpxchg to an A-B-A problem which allows reads\nfollowing the lock acquisition to observe values speculatively before\nthe write lock is truly acquired.\n\nWe've seen a problem in epoll where the reader does a xchg while\nholding the read lock, but the writer can see a value change out from\nunder it.\n\n  Writer                                | Reader\n  --------------------------------------------------------------------------------\n  ep_scan_ready_list()                  |\n  |- write_lock_irq()                   |\n      |- queued_write_lock_slowpath()   |\n\t|- atomic_cond_read_acquire()   |\n\t\t\t\t        | read_lock_irqsave(&ep->lock, flags);\n     --> (observes value before unlock) |  chain_epi_lockless()\n     |                                  |    epi->next = xchg(&ep->ovflist, epi);\n     |                                  | read_unlock_irqrestore(&ep->lock, flags);\n     |                                  |\n     |     atomic_cmpxchg_relaxed()     |\n     |-- READ_ONCE(ep->ovflist);        |\n\nA core can order the read of the ovflist ahead of the\natomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire\nsemantics addresses this issue at which point the atomic_cond_read can\nbe switched to use relaxed semantics.\n\n[peterz: use try_cmpxchg()]"
            }
         ],
         "affected": [
            {
               "product": "Linux",
               "vendor": "Linux",
               "defaultStatus": "unaffected",
               "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
               "programFiles": [
                  "kernel/locking/qrwlock.c"
               ],
               "versions": [
                  {
                     "version": "b519b56e378e",
                     "lessThan": "5902f9453a31",
                     "status": "affected",
                     "versionType": "git"
                  },
                  {
                     "version": "b519b56e378e",
                     "lessThan": "82808cc02681",
                     "status": "affected",
                     "versionType": "git"
                  },
                  {
                     "version": "b519b56e378e",
                     "lessThan": "82fa9ced35d8",
                     "status": "affected",
                     "versionType": "git"
                  },
                  {
                     "version": "b519b56e378e",
                     "lessThan": "d558fcdb1713",
                     "status": "affected",
                     "versionType": "git"
                  },
                  {
                     "version": "b519b56e378e",
                     "lessThan": "84a24bf8c52e",
                     "status": "affected",
                     "versionType": "git"
                  }
               ]
            },
            {
               "product": "Linux",
               "vendor": "Linux",
               "defaultStatus": "affected",
               "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
               "programFiles": [
                  "kernel/locking/qrwlock.c"
               ],
               "versions": [
                  {
                     "version": "4.15",
                     "status": "affected"
                  },
                  {
                     "version": "0",
                     "lessThan": "4.15",
                     "status": "unaffected",
                     "versionType": "custom"
                  },
                  {
                     "version": "4.19.189",
                     "lessThanOrEqual": "4.19.*",
                     "status": "unaffected",
                     "versionType": "custom"
                  },
                  {
                     "version": "5.4.115",
                     "lessThanOrEqual": "5.4.*",
                     "status": "unaffected",
                     "versionType": "custom"
                  },
                  {
                     "version": "5.10.33",
                     "lessThanOrEqual": "5.10.*",
                     "status": "unaffected",
                     "versionType": "custom"
                  },
                  {
                     "version": "5.11.17",
                     "lessThanOrEqual": "5.11.*",
                     "status": "unaffected",
                     "versionType": "custom"
                  },
                  {
                     "version": "5.12",
                     "lessThanOrEqual": "*",
                     "status": "unaffected",
                     "versionType": "original_commit_for_fix"
                  }
               ]
            }
         ],
         "references": [
            {
               "url": "https://git.kernel.org/stable/c/5902f9453a313be8fe78cbd7e7ca9dba9319fc6e"
            },
            {
               "url": "https://git.kernel.org/stable/c/82808cc026811fbc3ecf0c0b267a12a339eead56"
            },
            {
               "url": "https://git.kernel.org/stable/c/82fa9ced35d88581cffa4a1c856fc41fca96d80a"
            },
            {
               "url": "https://git.kernel.org/stable/c/d558fcdb17139728347bccc60a16af3e639649d2"
            },
            {
               "url": "https://git.kernel.org/stable/c/84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896"
            }
         ],
         "title": "locking/qrwlock: Fix ordering in queued_write_lock_slowpath()",
         "x_generator": {
            "engine": "bippy-a5840b7849dd"
         }
      }
   },
   "cveMetadata": {
      "assignerOrgId": "f4215fc3-5b6b-47ff-a258-f7189bd81038",
      "cveID": "CVE-2021-46921",
      "requesterUserId": "gregkh@kernel.org",
      "serial": "1",
      "state": "PUBLISHED"
   },
   "dataType": "CVE_RECORD",
   "dataVersion": "5.0"
}