In the Linux kernel, the following vulnerability has been resolved:

proc: protect ptrace_may_access() with exec_update_lock (FD links)

proc_pid_get_link() and proc_pid_readlink() currently look up the task from
the pid once, then do the ptrace access check on that task, then look up
the task from the pid a second time to do the actual access.
That's racy in several ways.

To fix it, pass the task to the ->proc_get_link() handler, and instead of
proc_fd_access_allowed(), introduce a new helper call_proc_get_link() that
looks up and locks the task, does the access check, and calls
->proc_get_link().

https://git.kernel.org/stable/c/138c692d2b2d63d26f2eb957d0e4fcc5d61f9ff2

https://git.kernel.org/stable/c/497c6bae5167428596575f20af6613ff5671f383

https://git.kernel.org/stable/c/6253dfee5afba536bb54fc6fe6c091c3758fafe1

https://git.kernel.org/stable/c/6255da28d4bb5349fe18e84cb043ccd394eba75d

https://git.kernel.org/stable/c/65bf0d2b6e914f1448d6a2fde193dcf60936a651

https://git.kernel.org/stable/c/83b17872e3166c295c599279fc9562ac3840c638

https://git.kernel.org/stable/c/de497d7aa2fae453a7e7c8f7d3e8682e565e3aaf

https://git.kernel.org/stable/c/dfd1894cb64cbd8758b461ed713800fe73db4f82

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