UBUNTU-CVE-2025-68772: Race Condition
In the Linux kernel, the following vulnerability has been resolved: f2fs: fix to avoid updating compression context during writeback Bai, Shuangpeng <sjb7183@psu.edu> reported a bug as below: Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 11441 Comm: syz.0.46 Not tainted 6.17.0 #1 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:f2fsallclusterpageready+0x106/0x550 fs/f2fs/compress.c:857 Call Trace: <TASK> f2fswritecachepages fs/f2fs/data.c:3078 [inline] f2fswritedatapages fs/f2fs/data.c:3290 [inline] f2fswritedatapages+0x1c19/0x3600 fs/f2fs/data.c:3317 dowritepages+0x38e/0x640 mm/page-writeback.c:2634 filemapfdatawritewbc mm/filemap.c:386 [inline] filemapfdatawriterange mm/filemap.c:419 [inline] filewriteandwaitrange+0x2ba/0x3e0 mm/filemap.c:794 f2fsdosyncfile+0x6e6/0x1b00 fs/f2fs/file.c:294 genericwritesync include/linux/fs.h:3043 [inline] f2fsfilewriteiter+0x76e/0x2700 fs/f2fs/file.c:5259 newsyncwrite fs/readwrite.c:593 [inline] vfswrite+0x7e9/0xe00 fs/readwrite.c:686 ksyswrite+0x19d/0x2d0 fs/readwrite.c:738 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xf7/0x470 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f The bug was triggered w/ below race condition: fsync setattr ioctl - f2fsdosyncfile - filewriteandwaitrange - f2fswritecachepages : inode is non-compressed : cc.clustersize = F2FSI(inode)->iclustersize = 0 - tagpagesforwriteback - f2fssetattr - truncatesetsize - f2fstruncate - f2fsfileattrset - f2fssetflagscommon - setcompresscontext : F2FSI(inode)->iclustersize = 4 : setinodeflag(inode, FICOMPRESSEDFILE) - f2fscompressedfile : return true - f2fsallclusterpageready : "pgidx % cc->clustersize" trigger dividing 0 issue Let's change as below to fix this issue: - introduce a new atomic type variable .writeback in structure f2fsinodeinfo to track the number of threads which calling f2fswritecachepages(). - use .isem lock to protect .writeback update. - check .writeback before update compression context in f2fssetflagscommon() to avoid race w/ ->writepages.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 6.17.0-22.22.1 - Compensating control
In f2fs_setflags_common(), check the f2fs_inode_info .writeback counter before updating the compression context, and protect .writeback updates with the .i_sem lock; introduce an atomic .writeback variable to track threads calling f2fs_write_cache_pages().
Event History
Frequently Asked Questions
What access does an attacker need to exploit this issue?
The vector is local and requires low privileges. No user interaction is required.
What is the expected security impact?
The provided severity vector indicates high availability impact, with no confidentiality or integrity impact. The reported failure is a kernel divide-error Oops during F2FS writeback.
How can I identify a potentially related failure?
Look for kernel Oops or divide-error reports during F2FS writeback, with stack frames including f2fs_all_cluster_page_ready, f2fs_write_data_pages, or f2fs_do_sync_file.