ghsa-f639-593q-rjgw
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: fix data corruption after conversion from inline format
Commit 6dbf7bb55598 ("fs: Don't invalidate page buffers in block_write_full_page()") uncovered a latent bug in ocfs2 conversion from inline inode format to a normal inode format.
The code in ocfs2_convert_inline_data_to_extents() attempts to zero out the whole cluster allocated for file data by grabbing, zeroing, and dirtying all pages covering this cluster. However these pages are beyond i_size, thus writeback code generally ignores these dirty pages and no blocks were ever actually zeroed on the disk.
This oversight was fixed by commit 693c241a5f6a ("ocfs2: No need to zero pages past i_size.") for standard ocfs2 write path, inline conversion path was apparently forgotten; the commit log also has a reasoning why the zeroing actually is not needed.
After commit 6dbf7bb55598, things became worse as writeback code stopped invalidating buffers on pages beyond i_size and thus these pages end up with clean PageDirty bit but with buffers attached to these pages being still dirty. So when a file is converted from inline format, then writeback triggers, and then the file is grown so that these pages become valid, the invalid dirtiness state is preserved, mark_buffer_dirty() does nothing on these pages (buffers are already dirty) but page is never written back because it is clean. So data written to these pages is lost once pages are reclaimed.
Simple reproducer for the problem is:
xfs_io -f -c "pwrite 0 2000" -c "pwrite 2000 2000" -c "fsync" \ -c "pwrite 4000 2000" ocfs2_file
After unmounting and mounting the fs again, you can observe that end of 'ocfs2_file' has lost its contents.
Fix the problem by not doing the pointless zeroing during conversion from inline format similarly as in the standard write path.
[akpm@linux-foundation.org: fix whitespace, per Joseph]
{
"affected": [],
"aliases": [
"CVE-2021-47460"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-05-22T07:15:10Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: fix data corruption after conversion from inline format\n\nCommit 6dbf7bb55598 (\"fs: Don\u0027t invalidate page buffers in\nblock_write_full_page()\") uncovered a latent bug in ocfs2 conversion\nfrom inline inode format to a normal inode format.\n\nThe code in ocfs2_convert_inline_data_to_extents() attempts to zero out\nthe whole cluster allocated for file data by grabbing, zeroing, and\ndirtying all pages covering this cluster. However these pages are\nbeyond i_size, thus writeback code generally ignores these dirty pages\nand no blocks were ever actually zeroed on the disk.\n\nThis oversight was fixed by commit 693c241a5f6a (\"ocfs2: No need to zero\npages past i_size.\") for standard ocfs2 write path, inline conversion\npath was apparently forgotten; the commit log also has a reasoning why\nthe zeroing actually is not needed.\n\nAfter commit 6dbf7bb55598, things became worse as writeback code stopped\ninvalidating buffers on pages beyond i_size and thus these pages end up\nwith clean PageDirty bit but with buffers attached to these pages being\nstill dirty. So when a file is converted from inline format, then\nwriteback triggers, and then the file is grown so that these pages\nbecome valid, the invalid dirtiness state is preserved,\nmark_buffer_dirty() does nothing on these pages (buffers are already\ndirty) but page is never written back because it is clean. So data\nwritten to these pages is lost once pages are reclaimed.\n\nSimple reproducer for the problem is:\n\n xfs_io -f -c \"pwrite 0 2000\" -c \"pwrite 2000 2000\" -c \"fsync\" \\\n -c \"pwrite 4000 2000\" ocfs2_file\n\nAfter unmounting and mounting the fs again, you can observe that end of\n\u0027ocfs2_file\u0027 has lost its contents.\n\nFix the problem by not doing the pointless zeroing during conversion\nfrom inline format similarly as in the standard write path.\n\n[akpm@linux-foundation.org: fix whitespace, per Joseph]",
"id": "GHSA-f639-593q-rjgw",
"modified": "2024-05-22T09:31:45Z",
"published": "2024-05-22T09:31:45Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-47460"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5314454ea3ff6fc746eaf71b9a7ceebed52888fa"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/560edd14de2bf9dbc0129681eeb4d5ef87cc105f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8e6bfb4f70168ddfd32fb6dc028ad52faaf1f32e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a3a089c241cd49b33a8cdd7fcb37cc87a086912a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b05caf023b14cbed9223bb5b48ecc7bffe38f632"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f1b98569e81c37d7e0deada7172f8f60860c1360"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fa9b6b6c953e3f6441ed6cf83b4c771dac2dae08"
}
],
"schema_version": "1.4.0",
"severity": []
}