ghsa-w9qv-8mcj-wh8f
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix race in read_extent_buffer_pages()
There are reports from tree-checker that detects corrupted nodes, without any obvious pattern so possibly an overwrite in memory. After some debugging it turns out there's a race when reading an extent buffer the uptodate status can be missed.
To prevent concurrent reads for the same extent buffer, read_extent_buffer_pages() performs these checks:
/* (1) */
if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
return 0;
/* (2) */
if (test_and_set_bit(EXTENT_BUFFER_READING, &eb->bflags))
goto done;
At this point, it seems safe to start the actual read operation. Once that completes, end_bbio_meta_read() does
/* (3) */
set_extent_buffer_uptodate(eb);
/* (4) */
clear_bit(EXTENT_BUFFER_READING, &eb->bflags);
Normally, this is enough to ensure only one read happens, and all other callers wait for it to finish before returning. Unfortunately, there is a racey interleaving:
Thread A | Thread B | Thread C
---------+----------+---------
(1) | |
| (1) |
(2) | |
(3) | |
(4) | |
| (2) |
| | (1)
When this happens, thread B kicks of an unnecessary read. Worse, thread C will see UPTODATE set and return immediately, while the read from thread B is still in progress. This race could result in tree-checker errors like this as the extent buffer is concurrently modified:
BTRFS critical (device dm-0): corrupted node, root=256
block=8550954455682405139 owner mismatch, have 11858205567642294356
expect [256, 18446744073709551360]
Fix it by testing UPTODATE again after setting the READING bit, and if it's been set, skip the unnecessary read.
[ minor update of changelog ]
{
"affected": [],
"aliases": [
"CVE-2024-35798"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-05-17T14:15:12Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix race in read_extent_buffer_pages()\n\nThere are reports from tree-checker that detects corrupted nodes,\nwithout any obvious pattern so possibly an overwrite in memory.\nAfter some debugging it turns out there\u0027s a race when reading an extent\nbuffer the uptodate status can be missed.\n\nTo prevent concurrent reads for the same extent buffer,\nread_extent_buffer_pages() performs these checks:\n\n /* (1) */\n if (test_bit(EXTENT_BUFFER_UPTODATE, \u0026eb-\u003ebflags))\n return 0;\n\n /* (2) */\n if (test_and_set_bit(EXTENT_BUFFER_READING, \u0026eb-\u003ebflags))\n goto done;\n\nAt this point, it seems safe to start the actual read operation. Once\nthat completes, end_bbio_meta_read() does\n\n /* (3) */\n set_extent_buffer_uptodate(eb);\n\n /* (4) */\n clear_bit(EXTENT_BUFFER_READING, \u0026eb-\u003ebflags);\n\nNormally, this is enough to ensure only one read happens, and all other\ncallers wait for it to finish before returning. Unfortunately, there is\na racey interleaving:\n\n Thread A | Thread B | Thread C\n ---------+----------+---------\n (1) | |\n | (1) |\n (2) | |\n (3) | |\n (4) | |\n | (2) |\n | | (1)\n\nWhen this happens, thread B kicks of an unnecessary read. Worse, thread\nC will see UPTODATE set and return immediately, while the read from\nthread B is still in progress. This race could result in tree-checker\nerrors like this as the extent buffer is concurrently modified:\n\n BTRFS critical (device dm-0): corrupted node, root=256\n block=8550954455682405139 owner mismatch, have 11858205567642294356\n expect [256, 18446744073709551360]\n\nFix it by testing UPTODATE again after setting the READING bit, and if\nit\u0027s been set, skip the unnecessary read.\n\n[ minor update of changelog ]",
"id": "GHSA-w9qv-8mcj-wh8f",
"modified": "2024-05-17T15:31:09Z",
"published": "2024-05-17T15:31:09Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-35798"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0427c8ef8bbb7f304de42ef51d69c960e165e052"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2885d54af2c2e1d910e20d5c8045bae40e02fbc1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3a25878a3378adce5d846300c9570f15aa7f7a80"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ef1e68236b9153c27cb7cf29ead0c532870d4215"
}
],
"schema_version": "1.4.0",
"severity": []
}