CVE-2022-49898 (GCVE-0-2022-49898)
Vulnerability from cvelistv5
Published
2025-05-01 14:10
Modified
2026-08-05 08:56
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix tree mod log mishandling of reallocated nodes
We have been seeing the following panic in production
kernel BUG at fs/btrfs/tree-mod-log.c:677!
invalid opcode: 0000 [#1] SMP
RIP: 0010:tree_mod_log_rewind+0x1b4/0x200
RSP: 0000:ffffc9002c02f890 EFLAGS: 00010293
RAX: 0000000000000003 RBX: ffff8882b448c700 RCX: 0000000000000000
RDX: 0000000000008000 RSI: 00000000000000a7 RDI: ffff88877d831c00
RBP: 0000000000000002 R08: 000000000000009f R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000100c40 R12: 0000000000000001
R13: ffff8886c26d6a00 R14: ffff88829f5424f8 R15: ffff88877d831a00
FS: 00007fee1d80c780(0000) GS:ffff8890400c0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fee1963a020 CR3: 0000000434f33002 CR4: 00000000007706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
btrfs_get_old_root+0x12b/0x420
btrfs_search_old_slot+0x64/0x2f0
? tree_mod_log_oldest_root+0x3d/0xf0
resolve_indirect_ref+0xfd/0x660
? ulist_alloc+0x31/0x60
? kmem_cache_alloc_trace+0x114/0x2c0
find_parent_nodes+0x97a/0x17e0
? ulist_alloc+0x30/0x60
btrfs_find_all_roots_safe+0x97/0x150
iterate_extent_inodes+0x154/0x370
? btrfs_search_path_in_tree+0x240/0x240
iterate_inodes_from_logical+0x98/0xd0
? btrfs_search_path_in_tree+0x240/0x240
btrfs_ioctl_logical_to_ino+0xd9/0x180
btrfs_ioctl+0xe2/0x2ec0
? __mod_memcg_lruvec_state+0x3d/0x280
? do_sys_openat2+0x6d/0x140
? kretprobe_dispatcher+0x47/0x70
? kretprobe_rethook_handler+0x38/0x50
? rethook_trampoline_handler+0x82/0x140
? arch_rethook_trampoline_callback+0x3b/0x50
? kmem_cache_free+0xfb/0x270
? do_sys_openat2+0xd5/0x140
__x64_sys_ioctl+0x71/0xb0
do_syscall_64+0x2d/0x40
Which is this code in tree_mod_log_rewind()
switch (tm->op) {
case BTRFS_MOD_LOG_KEY_REMOVE_WHILE_FREEING:
BUG_ON(tm->slot < n);
This occurs because we replay the nodes in order that they happened, and
when we do a REPLACE we will log a REMOVE_WHILE_FREEING for every slot,
starting at 0. 'n' here is the number of items in this block, which in
this case was 1, but we had 2 REMOVE_WHILE_FREEING operations.
The actual root cause of this was that we were replaying operations for
a block that shouldn't have been replayed. Consider the following
sequence of events
1. We have an already modified root, and we do a btrfs_get_tree_mod_seq().
2. We begin removing items from this root, triggering KEY_REPLACE for
it's child slots.
3. We remove one of the 2 children this root node points to, thus triggering
the root node promotion of the remaining child, and freeing this node.
4. We modify a new root, and re-allocate the above node to the root node of
this other root.
The tree mod log looks something like this
logical 0 op KEY_REPLACE (slot 1) seq 2
logical 0 op KEY_REMOVE (slot 1) seq 3
logical 0 op KEY_REMOVE_WHILE_FREEING (slot 0) seq 4
logical 4096 op LOG_ROOT_REPLACE (old logical 0) seq 5
logical 8192 op KEY_REMOVE_WHILE_FREEING (slot 1) seq 6
logical 8192 op KEY_REMOVE_WHILE_FREEING (slot 0) seq 7
logical 0 op LOG_ROOT_REPLACE (old logical 8192) seq 8
>From here the bug is triggered by the following steps
1. Call btrfs_get_old_root() on the new_root.
2. We call tree_mod_log_oldest_root(btrfs_root_node(new_root)), which is
currently logical 0.
3. tree_mod_log_oldest_root() calls tree_mod_log_search_oldest(), which
gives us the KEY_REPLACE seq 2, and since that's not a
LOG_ROOT_REPLACE we incorrectly believe that we don't have an old
root, because we expect that the most recent change should be a
LOG_ROOT_REPLACE.
4. Back in tree_mod_log_oldest_root() we don't have a LOG_ROOT_REPLACE,
so we don't set old_root, we simply use our e
---truncated---
References
Impacted products
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/btrfs/extent-tree.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "007058eb8292efc4c88f921752194b83269da085",
"status": "affected",
"version": "bd989ba359f2acb8bc5f5490e19010fc0a6f8356",
"versionType": "git"
},
{
"lessThan": "52b2b65c9eb56fd829dda323786db828627ff7e6",
"status": "affected",
"version": "bd989ba359f2acb8bc5f5490e19010fc0a6f8356",
"versionType": "git"
},
{
"lessThan": "968b71583130b6104c9f33ba60446d598e327a8b",
"status": "affected",
"version": "bd989ba359f2acb8bc5f5490e19010fc0a6f8356",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/btrfs/extent-tree.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "3.5"
},
{
"lessThan": "3.5",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.78",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.0.*",
"status": "unaffected",
"version": "6.0.8",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "6.1",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.15.78",
"versionStartIncluding": "3.5",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.0.8",
"versionStartIncluding": "3.5",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.1",
"versionStartIncluding": "3.5",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix tree mod log mishandling of reallocated nodes\n\nWe have been seeing the following panic in production\n\n kernel BUG at fs/btrfs/tree-mod-log.c:677!\n invalid opcode: 0000 [#1] SMP\n RIP: 0010:tree_mod_log_rewind+0x1b4/0x200\n RSP: 0000:ffffc9002c02f890 EFLAGS: 00010293\n RAX: 0000000000000003 RBX: ffff8882b448c700 RCX: 0000000000000000\n RDX: 0000000000008000 RSI: 00000000000000a7 RDI: ffff88877d831c00\n RBP: 0000000000000002 R08: 000000000000009f R09: 0000000000000000\n R10: 0000000000000000 R11: 0000000000100c40 R12: 0000000000000001\n R13: ffff8886c26d6a00 R14: ffff88829f5424f8 R15: ffff88877d831a00\n FS: 00007fee1d80c780(0000) GS:ffff8890400c0000(0000) knlGS:0000000000000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 00007fee1963a020 CR3: 0000000434f33002 CR4: 00000000007706e0\n DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\n DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\n PKRU: 55555554\n Call Trace:\n btrfs_get_old_root+0x12b/0x420\n btrfs_search_old_slot+0x64/0x2f0\n ? tree_mod_log_oldest_root+0x3d/0xf0\n resolve_indirect_ref+0xfd/0x660\n ? ulist_alloc+0x31/0x60\n ? kmem_cache_alloc_trace+0x114/0x2c0\n find_parent_nodes+0x97a/0x17e0\n ? ulist_alloc+0x30/0x60\n btrfs_find_all_roots_safe+0x97/0x150\n iterate_extent_inodes+0x154/0x370\n ? btrfs_search_path_in_tree+0x240/0x240\n iterate_inodes_from_logical+0x98/0xd0\n ? btrfs_search_path_in_tree+0x240/0x240\n btrfs_ioctl_logical_to_ino+0xd9/0x180\n btrfs_ioctl+0xe2/0x2ec0\n ? __mod_memcg_lruvec_state+0x3d/0x280\n ? do_sys_openat2+0x6d/0x140\n ? kretprobe_dispatcher+0x47/0x70\n ? kretprobe_rethook_handler+0x38/0x50\n ? rethook_trampoline_handler+0x82/0x140\n ? arch_rethook_trampoline_callback+0x3b/0x50\n ? kmem_cache_free+0xfb/0x270\n ? do_sys_openat2+0xd5/0x140\n __x64_sys_ioctl+0x71/0xb0\n do_syscall_64+0x2d/0x40\n\nWhich is this code in tree_mod_log_rewind()\n\n\tswitch (tm-\u003eop) {\n case BTRFS_MOD_LOG_KEY_REMOVE_WHILE_FREEING:\n\t\tBUG_ON(tm-\u003eslot \u003c n);\n\nThis occurs because we replay the nodes in order that they happened, and\nwhen we do a REPLACE we will log a REMOVE_WHILE_FREEING for every slot,\nstarting at 0. \u0027n\u0027 here is the number of items in this block, which in\nthis case was 1, but we had 2 REMOVE_WHILE_FREEING operations.\n\nThe actual root cause of this was that we were replaying operations for\na block that shouldn\u0027t have been replayed. Consider the following\nsequence of events\n\n1. We have an already modified root, and we do a btrfs_get_tree_mod_seq().\n2. We begin removing items from this root, triggering KEY_REPLACE for\n it\u0027s child slots.\n3. We remove one of the 2 children this root node points to, thus triggering\n the root node promotion of the remaining child, and freeing this node.\n4. We modify a new root, and re-allocate the above node to the root node of\n this other root.\n\nThe tree mod log looks something like this\n\n\tlogical 0\top KEY_REPLACE (slot 1)\t\t\tseq 2\n\tlogical 0\top KEY_REMOVE (slot 1)\t\t\tseq 3\n\tlogical 0\top KEY_REMOVE_WHILE_FREEING (slot 0)\tseq 4\n\tlogical 4096\top LOG_ROOT_REPLACE (old logical 0)\tseq 5\n\tlogical 8192\top KEY_REMOVE_WHILE_FREEING (slot 1)\tseq 6\n\tlogical 8192\top KEY_REMOVE_WHILE_FREEING (slot 0)\tseq 7\n\tlogical 0\top LOG_ROOT_REPLACE (old logical 8192)\tseq 8\n\n\u003eFrom here the bug is triggered by the following steps\n\n1. Call btrfs_get_old_root() on the new_root.\n2. We call tree_mod_log_oldest_root(btrfs_root_node(new_root)), which is\n currently logical 0.\n3. tree_mod_log_oldest_root() calls tree_mod_log_search_oldest(), which\n gives us the KEY_REPLACE seq 2, and since that\u0027s not a\n LOG_ROOT_REPLACE we incorrectly believe that we don\u0027t have an old\n root, because we expect that the most recent change should be a\n LOG_ROOT_REPLACE.\n4. Back in tree_mod_log_oldest_root() we don\u0027t have a LOG_ROOT_REPLACE,\n so we don\u0027t set old_root, we simply use our e\n---truncated---"
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - Reached through local VFS/ioctl paths on a mounted btrfs filesystem\u2014primarily FS_IOC_FIEMAP via btrfs_is_data_extent_shared \u2192 find_parent_nodes \u2192 btrfs_search_old_slot \u2192 tree_mod_log_rewind, and CAP_SYS_ADMIN LOGICAL_INO. No in-kernel network protocol handler (ksmbd/nfsd) directly executes this rewind logic on remote peer input.\nAC:L - An unprivileged attacker can keep a transaction open with concurrent writes while looping fiemap (joining that transaction and holding a tree-mod seq), and drive tree balancing/freeing so freed nodes are reused as roots of other trees\u2014the same sequence seen in production. Attacker-controlled concurrency and retries make success not dependent on conditions outside their influence.\nPR:L - fiemap requires only an open readable regular file on btrfs (e.g. under /home or /tmp); ioctl_fiemap/extent_fiemap perform no capability check before btrfs_is_data_extent_shared takes a tree-mod seq and enters the vulnerable rewind. LOGICAL_INO needs CAP_SYS_ADMIN, but the worst reachable case is unprivileged fiemap.\nUI:N - On an already-mounted btrfs volume the attacker creates/opens their own file, issues fiemap, and runs concurrent metadata-heavy writes themselves; no separate victim action such as mounting a crafted image is required.\nS:U - Impact is confined to the host kernel and the affected btrfs instance within one security authority; there is no VM escape, IOMMU bypass, or other cross-boundary effect.\nC:H - Replaying mod-log ops from a prior incarnation of a reallocated node reconstructs wrong child block pointers; search_old_slot then reads those bytenrs as nodes\u2014including blocks since reused for attacker-controlled data\u2014yielding arbitrary metadata/disk reads. With CONFIG_BUG=n the BUG_ON guard is compiled out so rewind continues into that confused walk (and oopses also dump register/stack state).\nI:H - The same incorrect rewind (and CONFIG_BUG=n continuation past BUG_ON(tm-\u003eslot \u003c n), including KEY_ADD nritems underflow) poisons the reconstructed node state used for further walks, so attacker-influenced block content interpreted as key_ptrs directs subsequent tree operations\u2014consistent with treating this class of metadata confusion as high integrity impact when the assertion is not a hard stop.\nA:H - The production failure is kernel BUG at tree_mod_log_rewind (invalid opcode), i.e. oops/panic; even without a full panic, crashing while holding tree-mod and path locks can wedge btrfs transactions and deny service for the filesystem/system."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-05T08:56:36.301Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/007058eb8292efc4c88f921752194b83269da085"
},
{
"url": "https://git.kernel.org/stable/c/52b2b65c9eb56fd829dda323786db828627ff7e6"
},
{
"url": "https://git.kernel.org/stable/c/968b71583130b6104c9f33ba60446d598e327a8b"
}
],
"title": "btrfs: fix tree mod log mishandling of reallocated nodes",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2022-49898",
"datePublished": "2025-05-01T14:10:44.873Z",
"dateReserved": "2025-05-01T14:05:17.244Z",
"dateUpdated": "2026-08-05T08:56:36.301Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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