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CVE-2025-21999 is a Linux kernel use-after-free vulnerability in the proc filesystem's proc_get_inode() path. The flaw is caused by a race condition between loadable module removal and inode instantiation for /proc entries. A proc directory entry may retain references to module-owned proc_ops, but those operations structures do not belong to /proc itself. During a concurrent sequence where one thread performs lookup and inode creation for a /proc entry while another unloads the backing module and removes the proc entry, proc_get_inode() can dereference proc_ops after the module memory has already been freed. In the demonstrated failure path, a regular-file proc inode instantiation can reach logic that checks proc_read_iter through the freed proc_ops pointer, resulting in a kernel page fault and KASAN-detected use-after-free. The upstream fix stores the information needed for inode instantiation in the proc directory entry before proc_register(), eliminating the unsafe later dereference of module-owned proc_ops during lookup.
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A Linux kernel use-after-free vulnerability in proc_get_inode().
A Linux kernel use-after-free vulnerability in proc_get_inode().
A Linux kernel use-after-free vulnerability in proc_get_inode().
A Linux kernel vulnerability involving a use-after-free in proc_get_inode().
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