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redhatcveRedhat.comRH:CVE-2024-35798
HistoryMay 18, 2024 - 1:03 a.m.

CVE-2024-35798

2024-05-1801:03:59
redhat.com
access.redhat.com
4
linux kernel
race condition
vulnerability
btrfs
corrupted nodes
read operation

6.6 Medium

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

15.5%

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 ---------Β±---------Β±-------- (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 ]

6.6 Medium

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

15.5%