SUNRPC: make sure cache entry active before cache_show

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: SUNRPC: make sure cache entry active before cache_show The function `c_show` was called with protection from RCU. This only ensures that `cp` will not be freed. Therefore, the reference count for `cp` can drop to zero, which will trigger a refcount use-after-free warning when `cache_get` is called. To resolve this issue, use `cache_get_rcu` to ensure that `cp` remains active. ------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. WARNING: CPU: 7 PID: 822 at lib/refcount.c:25 refcount_warn_saturate+0xb1/0x120 CPU: 7 UID: 0 PID: 822 Comm: cat Not tainted 6.12.0-rc3+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:refcount_warn_saturate+0xb1/0x120 Call Trace: <TASK> c_show+0x2fc/0x380 [sunrpc] seq_read_iter+0x589/0x770 seq_read+0x1e5/0x270 proc_reg_read+0xe1/0x140 vfs_read+0x125/0x530 ksys_read+0xc1/0x160 do_syscall_64+0x5f/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e

References

• https://git.kernel.org/stable/c/e9be26735d055c42543a4d047a769cc6d0fb1504
• https://git.kernel.org/stable/c/02999e135b013d85c6df738746e8e24699befee4
• https://git.kernel.org/stable/c/c7dac3af57e38b2054f990e573256d90bf887958
• https://git.kernel.org/stable/c/068c0b50f3f700b94f78850834cd91ae3b34c2c1
• https://git.kernel.org/stable/c/acfaf37888e0f0732fb6a50ff093dce6d99994d0
• https://git.kernel.org/stable/c/ec305f303bf070b4f6896b7a76009f702956d402
• https://git.kernel.org/stable/c/d882e2b7fad3f5e5fac66184a347f408813f654a
• https://git.kernel.org/stable/c/2862eee078a4d2d1f584e7f24fa50dddfa5f3471