CVE-2025-21999: proc: fix UAF in proc_get_inode()
First published: Thu Apr 03 2025(Updated: )
In the Linux kernel, the following vulnerability has been resolved: proc: fix UAF in proc_get_inode() Fix race between rmmod and /proc/XXX's inode instantiation. The bug is that pde->proc_ops don't belong to /proc, it belongs to a module, therefore dereferencing it after /proc entry has been registered is a bug unless use_pde/unuse_pde() pair has been used. use_pde/unuse_pde can be avoided (2 atomic ops!) because pde->proc_ops never changes so information necessary for inode instantiation can be saved _before_ proc_register() in PDE itself and used later, avoiding pde->proc_ops->... dereference. rmmod lookup sys_delete_module proc_lookup_de pde_get(de); proc_get_inode(dir->i_sb, de); mod->exit() proc_remove remove_proc_subtree proc_entry_rundown(de); free_module(mod); if (S_ISREG(inode->i_mode)) if (de->proc_ops->proc_read_iter) --> As module is already freed, will trigger UAF BUG: unable to handle page fault for address: fffffbfff80a702b PGD 817fc4067 P4D 817fc4067 PUD 817fc0067 PMD 102ef4067 PTE 0 Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI CPU: 26 UID: 0 PID: 2667 Comm: ls Tainted: G Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) RIP: 0010:proc_get_inode+0x302/0x6e0 RSP: 0018:ffff88811c837998 EFLAGS: 00010a06 RAX: dffffc0000000000 RBX: ffffffffc0538140 RCX: 0000000000000007 RDX: 1ffffffff80a702b RSI: 0000000000000001 RDI: ffffffffc0538158 RBP: ffff8881299a6000 R08: 0000000067bbe1e5 R09: 1ffff11023906f20 R10: ffffffffb560ca07 R11: ffffffffb2b43a58 R12: ffff888105bb78f0 R13: ffff888100518048 R14: ffff8881299a6004 R15: 0000000000000001 FS: 00007f95b9686840(0000) GS:ffff8883af100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: fffffbfff80a702b CR3: 0000000117dd2000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> proc_lookup_de+0x11f/0x2e0 __lookup_slow+0x188/0x350 walk_component+0x2ab/0x4f0 path_lookupat+0x120/0x660 filename_lookup+0x1ce/0x560 vfs_statx+0xac/0x150 __do_sys_newstat+0x96/0x110 do_syscall_64+0x5f/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e [adobriyan@gmail.com: don't do 2 atomic ops on the common path]
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Kernel | ||
| Linux Kernel | >=2.6.23<6.1.132 | |
| Linux Kernel | >=6.2<6.6.85 | |
| Linux Kernel | >=6.7<6.12.21 | |
| Linux Kernel | >=6.13<6.13.9 | |
| Linux Kernel | =6.14-rc1 | |
| Linux Kernel | =6.14-rc2 | |
| Linux Kernel | =6.14-rc3 | |
| Linux Kernel | =6.14-rc4 |
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Reference Links
- https://git.kernel.org/stable/c/966f331403dc3ed04ff64eaf3930cf1267965e53
- https://git.kernel.org/stable/c/63b53198aff2e4e6c5866a4ff73c7891f958ffa4
- https://git.kernel.org/stable/c/ede3e8ac90ae106f0b29cd759aadebc1568f1308
- https://git.kernel.org/stable/c/64dc7c68e040251d9ec6e989acb69f8f6ae4a10b
- https://git.kernel.org/stable/c/654b33ada4ab5e926cd9c570196fefa7bec7c1df
- https://git.kernel.org/stable/c/4b0b8445b6fd41e6f62ac90547a0ea9d348de3fa
- https://git.kernel.org/stable/c/eda279586e571b05dff44d48e05f8977ad05855d
Frequently Asked Questions
What is the severity of CVE-2025-21999?
CVE-2025-21999 has a moderate severity rating due to the potential for privilege escalation via a use-after-free condition in the Linux kernel.
How do I fix CVE-2025-21999?
To fix CVE-2025-21999, update your Linux kernel to the latest stable version that includes the patch for this vulnerability.
What systems are affected by CVE-2025-21999?
CVE-2025-21999 affects various versions of the Linux kernel that utilize the /proc file system.
What are the risks associated with CVE-2025-21999?
The risks of CVE-2025-21999 include potential unauthorized access and execution of arbitrary code by attackers.
Is there a workaround for CVE-2025-21999 if a patch is not available?
There is no reliable workaround for CVE-2025-21999, so applying the patch is strongly recommended.
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