248 lines
16 KiB
JSON
248 lines
16 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2021-46958",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2024-02-27T18:42:55.939Z",
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"datePublished": "2024-02-27T18:46:59.315Z",
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"dateUpdated": "2026-08-05T08:45:13.853Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix race between transaction aborts and fsyncs leading to use-after-free\n\nThere is a race between a task aborting a transaction during a commit,\na task doing an fsync and the transaction kthread, which leads to an\nuse-after-free of the log root tree. When this happens, it results in a\nstack trace like the following:\n\n BTRFS info (device dm-0): forced readonly\n BTRFS warning (device dm-0): Skipping commit of aborted transaction.\n BTRFS: error (device dm-0) in cleanup_transaction:1958: errno=-5 IO failure\n BTRFS warning (device dm-0): lost page write due to IO error on /dev/mapper/error-test (-5)\n BTRFS warning (device dm-0): Skipping commit of aborted transaction.\n BTRFS warning (device dm-0): direct IO failed ino 261 rw 0,0 sector 0xa4e8 len 4096 err no 10\n BTRFS error (device dm-0): error writing primary super block to device 1\n BTRFS warning (device dm-0): direct IO failed ino 261 rw 0,0 sector 0x12e000 len 4096 err no 10\n BTRFS warning (device dm-0): direct IO failed ino 261 rw 0,0 sector 0x12e008 len 4096 err no 10\n BTRFS warning (device dm-0): direct IO failed ino 261 rw 0,0 sector 0x12e010 len 4096 err no 10\n BTRFS: error (device dm-0) in write_all_supers:4110: errno=-5 IO failure (1 errors while writing supers)\n BTRFS: error (device dm-0) in btrfs_sync_log:3308: errno=-5 IO failure\n general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b68: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI\n CPU: 2 PID: 2458471 Comm: fsstress Not tainted 5.12.0-rc5-btrfs-next-84 #1\n Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014\n RIP: 0010:__mutex_lock+0x139/0xa40\n Code: c0 74 19 (...)\n RSP: 0018:ffff9f18830d7b00 EFLAGS: 00010202\n RAX: 6b6b6b6b6b6b6b68 RBX: 0000000000000001 RCX: 0000000000000002\n RDX: ffffffffb9c54d13 RSI: 0000000000000000 RDI: 0000000000000000\n RBP: ffff9f18830d7bc0 R08: 0000000000000000 R09: 0000000000000000\n R10: ffff9f18830d7be0 R11: 0000000000000001 R12: ffff8c6cd199c040\n R13: ffff8c6c95821358 R14: 00000000fffffffb R15: ffff8c6cbcf01358\n FS: 00007fa9140c2b80(0000) GS:ffff8c6fac600000(0000) knlGS:0000000000000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 00007fa913d52000 CR3: 000000013d2b4003 CR4: 0000000000370ee0\n DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\n DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\n Call Trace:\n ? __btrfs_handle_fs_error+0xde/0x146 [btrfs]\n ? btrfs_sync_log+0x7c1/0xf20 [btrfs]\n ? btrfs_sync_log+0x7c1/0xf20 [btrfs]\n btrfs_sync_log+0x7c1/0xf20 [btrfs]\n btrfs_sync_file+0x40c/0x580 [btrfs]\n do_fsync+0x38/0x70\n __x64_sys_fsync+0x10/0x20\n do_syscall_64+0x33/0x80\n entry_SYSCALL_64_after_hwframe+0x44/0xae\n RIP: 0033:0x7fa9142a55c3\n Code: 8b 15 09 (...)\n RSP: 002b:00007fff26278d48 EFLAGS: 00000246 ORIG_RAX: 000000000000004a\n RAX: ffffffffffffffda RBX: 0000563c83cb4560 RCX: 00007fa9142a55c3\n RDX: 00007fff26278cb0 RSI: 00007fff26278cb0 RDI: 0000000000000005\n RBP: 0000000000000005 R08: 0000000000000001 R09: 00007fff26278d5c\n R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000340\n R13: 00007fff26278de0 R14: 00007fff26278d96 R15: 0000563c83ca57c0\n Modules linked in: btrfs dm_zero dm_snapshot dm_thin_pool (...)\n ---[ end trace ee2f1b19327d791d ]---\n\nThe steps that lead to this crash are the following:\n\n1) We are at transaction N;\n\n2) We have two tasks with a transaction handle attached to transaction N.\n Task A and Task B. Task B is doing an fsync;\n\n3) Task B is at btrfs_sync_log(), and has saved fs_info->log_root_tree\n into a local variable named 'log_root_tree' at the top of\n btrfs_sync_log(). Task B is about to call write_all_supers(), but\n before that...\n\n4) Task A calls btrfs_commit_transaction(), and after it sets the\n transaction state to TRANS_STATE_COMMIT_START, an error happens before\n it w\n---truncated---"
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}
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - The vulnerable path is reached through local fsync/fdatasync on a mounted btrfs filesystem (fsync → btrfs_sync_file → btrfs_sync_log), not via network packet processing or physical device attachment.\nAC:L - An attacker controls both sides of the race by running concurrent threads that induce a transaction abort (many unprivileged write/create/unlink/ENOSPC abort sites) while another thread calls fsync, and can retry indefinitely until the kthread frees log_root_tree under the racing fsync.\nPR:L - Any unprivileged local user with access to a file on a mounted btrfs volume can call fsync and perform ordinary file operations that abort transactions; no capabilities or init-namespace root are required.\nUI:N - btrfs is commonly already mounted (desktops, NAS, Android, containers); the attacker drives writes and fsync from their own processes with no victim mount or open required.\nS:U - The use-after-free corrupts kernel heap state within the same OS/kernel security authority; there is no VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - The race frees the log_root_tree (struct btrfs_root) while btrfs_sync_log still holds and later dereferences that pointer (mutex_lock on log_mutex), which after slab reclaim/heap spray enables arbitrary kernel memory reads.\nI:H - Use-after-free of a kernel object with subsequent mutex and list operations on attacker-influenced freed memory yields write and control-flow hijack primitives suitable for privilege escalation.\nA:H - The demonstrated impact is a general protection fault / kernel oops in __mutex_lock via the freed log_root_tree pointer during fsync, which is a full host availability failure."
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