Re: [PATCH] Fix user data corrupted by old value return of sysctl

[David Wagner]

Yi Yang  wrote:
>If the user reads a sysctl entry which is of string type
>  by sysctl syscall, this call probably corrupts the user data
>  right after the old value buffer, the issue lies in sysctl_string
>  seting 0 to oldval[len], len is the available buffer size
>  specified by the user, obviously, this will write to the first
>  byte of the user memory place immediate after the old value buffer
>, the correct way is that sysctl_string doesn't set 0, the user
>should do it by self in the program.

That's not just data corruption -- it's also a buffer overrun.
Granted, it's "only" a one-byte overrun, but I have seen one-byte
overruns be exploitable occasionally in the past.  So this sounds
to me like a potential security issue, too.
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