CVE-2024-38306 SUSE CVE security@suse.de SUSE Security Team SUSE CVE-2024-38306 Interim 1 9 2025-08-13T23:48:38Z current 2024-06-29T17:05:09Z 2025-08-13T23:48:38Z cve-database/bin/generate-cvrf-cve.pl 2020-12-27T01:00:00Z CVE-2024-38306 In the Linux kernel, the following vulnerability has been resolved: btrfs: protect folio::private when attaching extent buffer folios [BUG] Since v6.8 there are rare kernel crashes reported by various people, the common factor is bad page status error messages like this: BUG: Bad page state in process kswapd0 pfn:d6e840 page: refcount:0 mapcount:0 mapping:000000007512f4f2 index:0x2796c2c7c pfn:0xd6e840 aops:btree_aops ino:1 flags: 0x17ffffe0000008(uptodate|node=0|zone=2|lastcpupid=0x3fffff) page_type: 0xffffffff() raw: 0017ffffe0000008 dead000000000100 dead000000000122 ffff88826d0be4c0 raw: 00000002796c2c7c 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: non-NULL mapping [CAUSE] Commit 09e6cef19c9f ("btrfs: refactor alloc_extent_buffer() to allocate-then-attach method") changes the sequence when allocating a new extent buffer. Previously we always called grab_extent_buffer() under mapping->i_private_lock, to ensure the safety on modification on folio::private (which is a pointer to extent buffer for regular sectorsize). This can lead to the following race: Thread A is trying to allocate an extent buffer at bytenr X, with 4 4K pages, meanwhile thread B is trying to release the page at X + 4K (the second page of the extent buffer at X). Thread A | Thread B -----------------------------------+------------------------------------- | btree_release_folio() | | This is for the page at X + 4K, | | Not page X. | | alloc_extent_buffer() | |- release_extent_buffer() |- filemap_add_folio() for the | | |- atomic_dec_and_test(eb->refs) | page at bytenr X (the first | | | | page). | | | | Which returned -EEXIST. | | | | | | | |- filemap_lock_folio() | | | | Returned the first page locked. | | | | | | | |- grab_extent_buffer() | | | | |- atomic_inc_not_zero() | | | | | Returned false | | | | |- folio_detach_private() | | |- folio_detach_private() for X | |- folio_test_private() | | |- folio_test_private() | Returned true | | | Returned true |- folio_put() | |- folio_put() Now there are two puts on the same folio at folio X, leading to refcount underflow of the folio X, and eventually causing the BUG_ON() on the page->mapping. The condition is not that easy to hit: - The release must be triggered for the middle page of an eb If the release is on the same first page of an eb, page lock would kick in and prevent the race. - folio_detach_private() has a very small race window It's only between folio_test_private() and folio_clear_private(). That's exactly when mapping->i_private_lock is used to prevent such race, and commit 09e6cef19c9f ("btrfs: refactor alloc_extent_buffer() to allocate-then-attach method") screwed that up. At that time, I thought the page lock would kick in as filemap_release_folio() also requires the page to be locked, but forgot the filemap_release_folio() only locks one page, not all pages of an extent buffer. [FIX] Move all the code requiring i_private_lock into attach_eb_folio_to_filemap(), so that everything is done with proper lock protection. Furthermore to prevent future problems, add an extra lockdep_assert_locked() to ensure we're holding the proper lock. To reproducer that is able to hit the race (takes a few minutes with instrumented code inserting delays to alloc_extent_buffer()): #!/bin/sh drop_caches () { while(true); do echo 3 > /proc/sys/vm/drop_caches echo 1 > /proc/sys/vm/compact_memory done } run_tar () { while(true); do for x in `seq 1 80` ; do tar cf /dev/zero /mnt > /dev/null & done wait done } mkfs.btrfs -f -d single -m single ---truncated--- The CVRF data is provided by SUSE under the Creative Commons License 4.0 with Attribution (CC-BY-4.0). https://www.suse.com/support/security/rating/ SUSE Security Ratings SUSE Enterprise Storage 7.1 SUSE Linux Enterprise Module for Basesystem 15 SP5 SUSE Linux Enterprise Module for Development Tools 15 SP5 SUSE Linux Enterprise Module for Basesystem 15 SP6 SUSE Linux Enterprise Module for Development Tools 15 SP6 SUSE Linux Enterprise High Performance Computing 12 SP5 SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS SUSE Linux Enterprise High Performance Computing 15 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15.6 kernel-default-livepatch as a component of openSUSE Leap 15.6 kernel-default-livepatch-devel as a component of openSUSE Leap 15.6 kernel-default-optional as a component of openSUSE Leap 15.6 kernel-default-vdso as a component of openSUSE Leap 15.6 kselftests-kmp-default as a component of openSUSE Leap 15.6 ocfs2-kmp-default as a component of openSUSE Leap 15.6 reiserfs-kmp-default as a component of openSUSE Leap 15.6 kernel-devel as a component of openSUSE Leap 15.6 kernel-macros as a component of openSUSE Leap 15.6 kernel-source as a component of openSUSE Leap 15.6 kernel-source-vanilla as a component of openSUSE Leap 15.6 kernel-devel-azure as a component of openSUSE Leap 15.6 kernel-source-azure as a component of openSUSE Leap 15.6 kernel-devel-rt as a component of openSUSE Leap 15.6 kernel-source-rt as a component of openSUSE Leap 15.6 In the Linux kernel, the following vulnerability has been resolved: btrfs: protect folio::private when attaching extent buffer folios [BUG] Since v6.8 there are rare kernel crashes reported by various people, the common factor is bad page status error messages like this: BUG: Bad page state in process kswapd0 pfn:d6e840 page: refcount:0 mapcount:0 mapping:000000007512f4f2 index:0x2796c2c7c pfn:0xd6e840 aops:btree_aops ino:1 flags: 0x17ffffe0000008(uptodate|node=0|zone=2|lastcpupid=0x3fffff) page_type: 0xffffffff() raw: 0017ffffe0000008 dead000000000100 dead000000000122 ffff88826d0be4c0 raw: 00000002796c2c7c 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: non-NULL mapping [CAUSE] Commit 09e6cef19c9f ("btrfs: refactor alloc_extent_buffer() to allocate-then-attach method") changes the sequence when allocating a new extent buffer. Previously we always called grab_extent_buffer() under mapping->i_private_lock, to ensure the safety on modification on folio::private (which is a pointer to extent buffer for regular sectorsize). This can lead to the following race: Thread A is trying to allocate an extent buffer at bytenr X, with 4 4K pages, meanwhile thread B is trying to release the page at X + 4K (the second page of the extent buffer at X). Thread A | Thread B -----------------------------------+------------------------------------- | btree_release_folio() | | This is for the page at X + 4K, | | Not page X. | | alloc_extent_buffer() | |- release_extent_buffer() |- filemap_add_folio() for the | | |- atomic_dec_and_test(eb->refs) | page at bytenr X (the first | | | | page). | | | | Which returned -EEXIST. | | | | | | | |- filemap_lock_folio() | | | | Returned the first page locked. | | | | | | | |- grab_extent_buffer() | | | | |- atomic_inc_not_zero() | | | | | Returned false | | | | |- folio_detach_private() | | |- folio_detach_private() for X | |- folio_test_private() | | |- folio_test_private() | Returned true | | | Returned true |- folio_put() | |- folio_put() Now there are two puts on the same folio at folio X, leading to refcount underflow of the folio X, and eventually causing the BUG_ON() on the page->mapping. The condition is not that easy to hit: - The release must be triggered for the middle page of an eb If the release is on the same first page of an eb, page lock would kick in and prevent the race. - folio_detach_private() has a very small race window It's only between folio_test_private() and folio_clear_private(). That's exactly when mapping->i_private_lock is used to prevent such race, and commit 09e6cef19c9f ("btrfs: refactor alloc_extent_buffer() to allocate-then-attach method") screwed that up. At that time, I thought the page lock would kick in as filemap_release_folio() also requires the page to be locked, but forgot the filemap_release_folio() only locks one page, not all pages of an extent buffer. [FIX] Move all the code requiring i_private_lock into attach_eb_folio_to_filemap(), so that everything is done with proper lock protection. Furthermore to prevent future problems, add an extra lockdep_assert_locked() to ensure we're holding the proper lock. To reproducer that is able to hit the race (takes a few minutes with instrumented code inserting delays to alloc_extent_buffer()): #!/bin/sh drop_caches () { while(true); do echo 3 > /proc/sys/vm/drop_caches echo 1 > /proc/sys/vm/compact_memory done } run_tar () { while(true); do for x in `seq 1 80` ; do tar cf /dev/zero /mnt > /dev/null & done wait done } mkfs.btrfs -f -d single -m single ---truncated--- CVE-2024-38306 SUSE Enterprise Storage 7.1:kernel-default SUSE Enterprise Storage 7.1:kernel-default-devel SUSE Enterprise Storage 7.1:kernel-devel SUSE Enterprise Storage 7.1:kernel-macros SUSE Enterprise Storage 7.1:kernel-source SUSE Enterprise Storage 7.1:reiserfs-kmp-default SUSE Linux Enterprise High Performance Computing 12 SP5:kernel-default SUSE Linux Enterprise High Performance Computing 12 SP5:kernel-source SUSE Linux Enterprise High Performance Computing 12 SP5:kernel-source-azure SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:reiserfs-kmp-default SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:reiserfs-kmp-default SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:reiserfs-kmp-default SUSE Linux Enterprise Micro 5.0:kernel-default SUSE Linux Enterprise Micro 5.1:kernel-default SUSE Linux Enterprise Micro 5.1:kernel-rt SUSE Linux Enterprise Micro 5.1:kernel-source-rt SUSE Linux Enterprise Micro 5.2:kernel-default SUSE Linux Enterprise Micro 5.2:kernel-rt SUSE Linux Enterprise Micro 5.2:kernel-source-rt SUSE Linux Enterprise Micro 5.3:kernel-default SUSE Linux Enterprise Micro 5.3:kernel-rt SUSE Linux Enterprise Micro 5.3:kernel-source-rt SUSE Linux Enterprise Micro 5.4:kernel-default SUSE Linux Enterprise Micro 5.4:kernel-rt SUSE Linux Enterprise Micro 5.4:kernel-source-rt SUSE Linux Enterprise Micro 5.5:kernel-devel-rt SUSE Linux Enterprise Micro 5.5:kernel-source-rt SUSE Linux Enterprise Module for Basesystem 15 SP5:kernel-default SUSE Linux Enterprise Module for Basesystem 15 SP5:kernel-default-devel SUSE Linux Enterprise Module for Basesystem 15 SP5:kernel-devel SUSE Linux Enterprise Module for Basesystem 15 SP5:kernel-macros SUSE Linux Enterprise Module for Basesystem 15 SP5:kernel-source SUSE Linux Enterprise Module for Basesystem 15 SP6:kernel-default SUSE Linux Enterprise Module for Basesystem 15 SP6:kernel-default-devel SUSE Linux Enterprise Module for Basesystem 15 SP6:kernel-devel SUSE Linux Enterprise Module for Basesystem 15 SP6:kernel-macros SUSE Linux Enterprise Module for Basesystem 15 SP6:kernel-source SUSE Linux Enterprise Module for Development Tools 15 SP5:kernel-default SUSE Linux Enterprise Module for Development Tools 15 SP5:kernel-source SUSE Linux Enterprise Module for Development Tools 15 SP6:kernel-default SUSE Linux Enterprise Module for Development Tools 15 SP6:kernel-source SUSE Linux Enterprise Module for Public Cloud 15 SP5:kernel-devel-azure SUSE Linux Enterprise Module for Public Cloud 15 SP5:kernel-source-azure SUSE Linux Enterprise Module for Public Cloud 15 SP6:kernel-devel-azure SUSE Linux Enterprise Module for Public Cloud 15 SP6:kernel-source-azure SUSE Linux Enterprise Real Time 12 SP5:kernel-devel-rt SUSE Linux Enterprise Real Time 12 SP5:kernel-source-rt SUSE Linux Enterprise Server 11 SP4 LTSS EXTREME CORE:kernel-default SUSE Linux Enterprise Server 11 SP4 LTSS EXTREME CORE:kernel-default-base SUSE Linux Enterprise Server 11 SP4 LTSS EXTREME CORE:kernel-default-devel SUSE Linux Enterprise Server 11 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Time Module 15 SP6:kernel-source-rt openSUSE Leap 15.5:cluster-md-kmp-default openSUSE Leap 15.5:dlm-kmp-default openSUSE Leap 15.5:gfs2-kmp-default openSUSE Leap 15.5:kernel-default openSUSE Leap 15.5:kernel-default-devel openSUSE Leap 15.5:kernel-default-extra openSUSE Leap 15.5:kernel-default-livepatch openSUSE Leap 15.5:kernel-default-livepatch-devel openSUSE Leap 15.5:kernel-default-optional openSUSE Leap 15.5:kernel-default-vdso openSUSE Leap 15.5:kernel-devel openSUSE Leap 15.5:kernel-devel-azure openSUSE Leap 15.5:kernel-devel-rt openSUSE Leap 15.5:kernel-macros openSUSE Leap 15.5:kernel-source openSUSE Leap 15.5:kernel-source-azure openSUSE Leap 15.5:kernel-source-rt openSUSE Leap 15.5:kernel-source-vanilla openSUSE Leap 15.5:kselftests-kmp-default openSUSE Leap 15.5:ocfs2-kmp-default openSUSE Leap 15.5:reiserfs-kmp-default openSUSE Leap 15.6:cluster-md-kmp-default openSUSE Leap 15.6:dlm-kmp-default openSUSE Leap 15.6:gfs2-kmp-default openSUSE Leap 15.6:kernel-default openSUSE Leap 15.6:kernel-default-devel openSUSE Leap 15.6:kernel-default-extra openSUSE Leap 15.6:kernel-default-livepatch openSUSE Leap 15.6:kernel-default-livepatch-devel openSUSE Leap 15.6:kernel-default-optional openSUSE Leap 15.6:kernel-default-vdso openSUSE Leap 15.6:kernel-devel openSUSE Leap 15.6:kernel-devel-azure openSUSE Leap 15.6:kernel-devel-rt openSUSE Leap 15.6:kernel-macros openSUSE Leap 15.6:kernel-source openSUSE Leap 15.6:kernel-source-azure openSUSE Leap 15.6:kernel-source-rt openSUSE Leap 15.6:kernel-source-vanilla openSUSE Leap 15.6:kselftests-kmp-default openSUSE Leap 15.6:ocfs2-kmp-default openSUSE Leap 15.6:reiserfs-kmp-default important 7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H