UBUNTU-CVE-2026-31450: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: ext4: publish jinode after initialization ext4inodeattachjinode() publishes ei->jinode to concurrent users. It used to set ei->jinode before jbd2journalinitjbdinode(), allowing a reader to observe a non-NULL jinode with ivfsinode still unset. The fast commit flush path can then pass this jinode to jbd2waitinodedata(), which dereferences ivfsinode->imapping and may crash. Below is the crash I observe: BUG: unable to handle page fault for address: 000000010beb47f4 PGD 110e51067 P4D 110e51067 PUD 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 1 UID: 0 PID: 4850 Comm: fcfsyncbench Not tainted 6.18.0-00764-g795a690c06a5 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.17.0-2-2 04/01/2014 RIP: 0010:xasfindmarked+0x3d/0x2e0 Code: e0 03 48 83 f8 02 0f 84 f0 01 00 00 48 8b 47 08 48 89 c3 48 39 c6 0f 82 fd 01 00 00 48 85 c9 74 3d 48 83 f9 03 77 63 4c 8b 0f <49> 8b 71 08 48 c7 47 18 00 00 00 00 48 89 f1 83 e1 03 48 83 f9 02 RSP: 0018:ffffbbee806e7bf0 EFLAGS: 00010246 RAX: 000000000010beb4 RBX: 000000000010beb4 RCX: 0000000000000003 RDX: 0000000000000001 RSI: 0000002000300000 RDI: ffffbbee806e7c10 RBP: 0000000000000001 R08: 0000002000300000 R09: 000000010beb47ec R10: ffff9ea494590090 R11: 0000000000000000 R12: 0000002000300000 R13: ffffbbee806e7c90 R14: ffff9ea494513788 R15: ffffbbee806e7c88 FS: 00007fc2f9e3e6c0(0000) GS:ffff9ea6b1444000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000010beb47f4 CR3: 0000000119ac5000 CR4: 0000000000750ef0 PKRU: 55555554 Call Trace: <TASK> filemapgetfoliostag+0x87/0x2a0 filemapfdatawaitrange+0x5f/0xd0 ? srsoaliasreturnthunk+0x5/0xfbef5 ? schedule+0x3e7/0x10c0 ? srsoaliasreturnthunk+0x5/0xfbef5 ? srsoaliasreturnthunk+0x5/0xfbef5 ? srsoaliasreturnthunk+0x5/0xfbef5 ? preemptcountsub+0x5f/0x80 ? srsoaliasreturnthunk+0x5/0xfbef5 ? capsafenice+0x37/0x70 ? srsoaliasreturnthunk+0x5/0xfbef5 ? preemptcountsub+0x5f/0x80 ? srsoaliasreturnthunk+0x5/0xfbef5 filemapfdatawaitrangekeeperrors+0x12/0x40 ext4fccommit+0x697/0x8b0 ? ext4filewriteiter+0x64b/0x950 ? srsoaliasreturnthunk+0x5/0xfbef5 ? preemptcountsub+0x5f/0x80 ? srsoaliasreturnthunk+0x5/0xfbef5 ? vfswrite+0x356/0x480 ? srsoaliasreturnthunk+0x5/0xfbef5 ? preemptcountsub+0x5f/0x80 ext4syncfile+0xf7/0x370 dofsync+0x3b/0x80 ? syscalltraceenter+0x108/0x1d0 x64sysfdatasync+0x16/0x20 dosyscall64+0x62/0x2c0 entrySYSCALL64afterhwframe+0x76/0x7e ... Fix this by initializing the jbd2inode first. Use smpwmb() and WRITEONCE() to publish ei->jinode after initialization. Readers use READONCE() to fetch the pointer.
Affected Software
Remediation
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