CVE-2021-47460

Description

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]

Gravité et risque d'exploitation

CVE-2021-47460 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.21 %, ce qui la place devant 10.6 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions 4.14.204, 4.14.253, 0, 5.4.156, <a3a089c241cd49b33a8cdd7fcb37cc87a086912a, <f1b98569e81c37d7e0deada7172f8f60860c1360, 4.9.288, <560edd14de2bf9dbc0129681eeb4d5ef87cc105f, 4.19.155, <fa9b6b6c953e3f6441ed6cf83b4c771dac2dae08, <=4.9.*, 4.19.214, <=4.14.*, <8e6bfb4f70168ddfd32fb6dc028ad52faaf1f32e, 5.4.75, <=5.10.*, 36ed9e604215f58cec0381ca5fcc6da05f2d87ca, <=5.4.*, <5.10, <5314454ea3ff6fc746eaf71b9a7ceebed52888fa, <=4.19.*, 5.15, acef5107e2eacb08a16ad5db60320d65bd26a6c0, 4.9.242, <4.19.214, 5.10, <=*, <5.4.156, 5.9.5, 6dbf7bb555981fb5faf7b691e8f6169fc2b2e63b, <4.14.253, f8a6a2ed4b7d1c3c8631eeb6d00572bc853094a8, <4.9.288, 5.10.76, 5.14.15, 7ed80e77c908cbaa686529a49f8ae0060c5caee7, <=5.14.*, <b05caf023b14cbed9223bb5b48ecc7bffe38f632, 7ce2b16bad2cbfa3fa7bbc42c4448914f639ca47) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/560edd14de2bf9dbc0129681eeb4d5ef87cc105f
• https://git.kernel.org/stable/c/8e6bfb4f70168ddfd32fb6dc028ad52faaf1f32e
• https://git.kernel.org/stable/c/a3a089c241cd49b33a8cdd7fcb37cc87a086912a
• https://git.kernel.org/stable/c/b05caf023b14cbed9223bb5b48ecc7bffe38f632
• https://git.kernel.org/stable/c/f1b98569e81c37d7e0deada7172f8f60860c1360
• https://git.kernel.org/stable/c/fa9b6b6c953e3f6441ed6cf83b4c771dac2dae08
• https://git.kernel.org/stable/c/5314454ea3ff6fc746eaf71b9a7ceebed52888fa