{"id":"CVE-2024-49868","summary":"btrfs: fix a NULL pointer dereference when failed to start a new trasacntion","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix a NULL pointer dereference when failed to start a new trasacntion\n\n[BUG]\nSyzbot reported a NULL pointer dereference with the following crash:\n\n  FAULT_INJECTION: forcing a failure.\n   start_transaction+0x830/0x1670 fs/btrfs/transaction.c:676\n   prepare_to_relocate+0x31f/0x4c0 fs/btrfs/relocation.c:3642\n   relocate_block_group+0x169/0xd20 fs/btrfs/relocation.c:3678\n  ...\n  BTRFS info (device loop0): balance: ended with status: -12\n  Oops: general protection fault, probably for non-canonical address 0xdffffc00000000cc: 0000 [#1] PREEMPT SMP KASAN NOPTI\n  KASAN: null-ptr-deref in range [0x0000000000000660-0x0000000000000667]\n  RIP: 0010:btrfs_update_reloc_root+0x362/0xa80 fs/btrfs/relocation.c:926\n  Call Trace:\n   \u003cTASK\u003e\n   commit_fs_roots+0x2ee/0x720 fs/btrfs/transaction.c:1496\n   btrfs_commit_transaction+0xfaf/0x3740 fs/btrfs/transaction.c:2430\n   del_balance_item fs/btrfs/volumes.c:3678 [inline]\n   reset_balance_state+0x25e/0x3c0 fs/btrfs/volumes.c:3742\n   btrfs_balance+0xead/0x10c0 fs/btrfs/volumes.c:4574\n   btrfs_ioctl_balance+0x493/0x7c0 fs/btrfs/ioctl.c:3673\n   vfs_ioctl fs/ioctl.c:51 [inline]\n   __do_sys_ioctl fs/ioctl.c:907 [inline]\n   __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893\n   do_syscall_x64 arch/x86/entry/common.c:52 [inline]\n   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\n[CAUSE]\nThe allocation failure happens at the start_transaction() inside\nprepare_to_relocate(), and during the error handling we call\nunset_reloc_control(), which makes fs_info-\u003ebalance_ctl to be NULL.\n\nThen we continue the error path cleanup in btrfs_balance() by calling\nreset_balance_state() which will call del_balance_item() to fully delete\nthe balance item in the root tree.\n\nHowever during the small window between set_reloc_contrl() and\nunset_reloc_control(), we can have a subvolume tree update and created a\nreloc_root for that subvolume.\n\nThen we go into the final btrfs_commit_transaction() of\ndel_balance_item(), and into btrfs_update_reloc_root() inside\ncommit_fs_roots().\n\nThat function checks if fs_info-\u003ereloc_ctl is in the merge_reloc_tree\nstage, but since fs_info-\u003ereloc_ctl is NULL, it results a NULL pointer\ndereference.\n\n[FIX]\nJust add extra check on fs_info-\u003ereloc_ctl inside\nbtrfs_update_reloc_root(), before checking\nfs_info-\u003ereloc_ctl-\u003emerge_reloc_tree.\n\nThat DEAD_RELOC_TREE handling is to prevent further modification to the\nreloc tree during merge stage, but since there is no reloc_ctl at all,\nwe do not need to bother that.","modified":"2026-04-02T12:20:58.968555Z","published":"2024-10-21T18:01:10.722Z","related":["MGASA-2024-0344","MGASA-2024-0345","SUSE-SU-2024:4314-1","SUSE-SU-2024:4315-1","SUSE-SU-2024:4316-1","SUSE-SU-2024:4318-1","SUSE-SU-2024:4364-1","SUSE-SU-2024:4367-1","SUSE-SU-2024:4376-1","SUSE-SU-2024:4387-1","SUSE-SU-2025:0035-1","SUSE-SU-2025:20163-1","SUSE-SU-2025:20164-1","SUSE-SU-2025:20246-1","SUSE-SU-2025:20247-1","USN-7276-1","USN-7277-1","openSUSE-SU-2024:14500-1","openSUSE-SU-2025:14705-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/49xxx/CVE-2024-49868.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/1282f001cbf56e5dd6e90a18e205a566793f4be0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/37fee9c220b92c3b7bf22b51c51dde5364e7590b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/39356ec0e319ed07627b3a0f402d0608546509e6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7ad0c5868f2f0418619089513d95230c66cb7eb4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c3b47f49e83197e8dffd023ec568403bcdbb774b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d13249c0df7aab885acb149695f82c54c0822a70"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d73d48acf36f57362df7e4f9d76568168bf5e944"},{"type":"WEB","url":"https://git.kernel.org/stable/c/dc02c1440705e3451abd1c2c8114a5c1bb188e9f"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/49xxx/CVE-2024-49868.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-49868"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"3fd0a5585eb98e074fb9934549c8d85c49756c0d"},{"fixed":"1282f001cbf56e5dd6e90a18e205a566793f4be0"},{"fixed":"d73d48acf36f57362df7e4f9d76568168bf5e944"},{"fixed":"37fee9c220b92c3b7bf22b51c51dde5364e7590b"},{"fixed":"d13249c0df7aab885acb149695f82c54c0822a70"},{"fixed":"7ad0c5868f2f0418619089513d95230c66cb7eb4"},{"fixed":"dc02c1440705e3451abd1c2c8114a5c1bb188e9f"},{"fixed":"39356ec0e319ed07627b3a0f402d0608546509e6"},{"fixed":"c3b47f49e83197e8dffd023ec568403bcdbb774b"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-49868.json"}}],"schema_version":"1.7.5"}