UBUNTU-CVE-2024-47736
In the Linux kernel, the following vulnerability has been resolved: erofs: handle overlapped pclusters out of crafted images properly syzbot reported a task hang issue due to a deadlock case where it is waiting for the folio lock of a cached folio that will be used for cache I/Os. After looking into the crafted fuzzed image, I found it's formed with several overlapped big pclusters as below: Ext: logical offset | length : physical offset | length 0: 0.. 16384 | 16384 : 151552.. 167936 | 16384 1: 16384.. 32768 | 16384 : 155648.. 172032 | 16384 2: 32768.. 49152 | 16384 : 537223168.. 537239552 | 16384 ... Here, extent 0/1 are physically overlapped although it's entirely _impossible_ for normal filesystem images generated by mkfs. First, managed folios containing compressed data will be marked as up-to-date and then unlocked immediately (unlike in-place folios) when compressed I/Os are complete. If physical blocks are not submitted in the incremental order, there should be separate BIOs to avoid dependency issues. However, the current code mis-arranges z_erofs_fill_bio_vec() and BIO submission which causes unexpected BIO waits. Second, managed folios will be connected to their own pclusters for efficient inter-queries. However, this is somewhat hard to implement easily if overlapped big pclusters exist. Again, these only appear in fuzzed images so let's simply fall back to temporary short-lived pages for correctness. Additionally, it justifies that referenced managed folios cannot be truncated for now and reverts part of commit 2080ca1ed3e4 ("erofs: tidy up `struct z_erofs_bvec`") for simplicity although it shouldn't be any difference.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
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26 explicit affected versions
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51 explicit affected versions
7 explicit affected versions
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71 explicit affected versions
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55 explicit affected versions
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10 explicit affected versions
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13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
2 explicit affected versions
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3 explicit affected versions
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26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
27 explicit affected versions
14 explicit affected versions
38 explicit affected versions
9 explicit affected versions
11 explicit affected versions
17 explicit affected versions
7 explicit affected versions
92 explicit affected versions
7 explicit affected versions
4 explicit affected versions
81 explicit affected versions
1 explicit affected versions
1 explicit affected versions
1 explicit affected versions
91 explicit affected versions
80 explicit affected versions
79 explicit affected versions
13 explicit affected versions
43 explicit affected versions
10 explicit affected versions
8 explicit affected versions
21 explicit affected versions
14 explicit affected versions
4 explicit affected versions
11 explicit affected versions
1 explicit affected versions
16 explicit affected versions
80 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: erofs: handle overlapped pclusters out of crafted images properly syzbot reported a task hang issue due to a deadlock case where it is waiting for the folio lock of a cached folio that will be used for cache I/Os. After looking into the crafted fuzzed image, I found it's formed with several overlapped big pclusters as below: Ext: logical offset | length : physical offset | length 0: 0.. 16384 | 16384 : 151552.. 167936 | 16384 1: 16384.. 32768 | 16384 : 155648.. 172032 | 16384 2: 32768.. 49152 | 16384 : 537223168.. 537239552 | 16384 ... Here, extent 0/1 are physically overlapped although it's entirely _impossible_ for normal filesystem images generated by mkfs. First, managed folios containing compressed data will be marked as up-to-date and then unlocked immediately (unlike in-place folios) when compressed I/Os are complete. If physical blocks are not submitted in the incremental order, there should be separate BIOs to avoid dependency issues. However, the current code mis-arranges z_erofs_fill_bio_vec() and BIO submission which causes unexpected BIO waits. Second, managed folios will be connected to their own pclusters for efficient inter-queries. However, this is somewhat hard to implement easily if overlapped big pclusters exist. Again, these only appear in fuzzed images so let's simply fall back to temporary short-lived pages for correctness. Additionally, it justifies that referenced managed folios cannot be truncated for now and reverts part of commit 2080ca1ed3e4 ("erofs: tidy up `struct z_erofs_bvec`") for simplicity although it shouldn't be any difference.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50
- https://git.kernel.org/stable/c/9cfa199bcbbbba31cbf97b2786f44f4464f3f29a
- https://git.kernel.org/stable/c/9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50
- https://git.kernel.org/stable/c/b9b30af0e86ffb485301ecd83b9129c9dfb7ebf8
- https://ubuntu.com/security/CVE-2024-47736
- https://ubuntu.com/security/notices/USN-7276-1
- https://ubuntu.com/security/notices/USN-7277-1
- https://ubuntu.com/security/notices/USN-7310-1
- https://ubuntu.com/security/notices/USN-7513-1
- https://ubuntu.com/security/notices/USN-7513-2
- https://ubuntu.com/security/notices/USN-7513-3
- https://ubuntu.com/security/notices/USN-7513-4
- https://ubuntu.com/security/notices/USN-7513-5
- https://ubuntu.com/security/notices/USN-7514-1
- https://ubuntu.com/security/notices/USN-7515-1
- https://ubuntu.com/security/notices/USN-7515-2
- https://ubuntu.com/security/notices/USN-7522-1
- https://ubuntu.com/security/notices/USN-7523-1
- https://ubuntu.com/security/notices/USN-7524-1
- https://www.cve.org/CVERecord?id=CVE-2024-47736