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    SubjectRe: [PATCH] proc: fix null pointer deref in proc_pid_permission()
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    On Wed, Jan 11, 2012 at 1:58 PM, Andrew Morton
    <akpm@linux-foundation.org> wrote:
    > On Wed, 11 Jan 2012 12:43:30 -0800
    > Kees Cook <keescook@chromium.org> wrote:
    >> On Wed, Jan 11, 2012 at 01:47:05PM -0500, Xiaotian Feng wrote:
    >> > get_proc_task() can fail to search the task and return NULL, put_task_struct()
    >> > will then bomb the kernel with following oops:
    >> >
    >> > [ 1870.574045] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
    >> > [ 1870.574065] IP: [<ffffffff81217d34>] proc_pid_permission+0x64/0xe0
    >> > [ 1870.574088] PGD 112075067 PUD 112814067 PMD 0
    >> > [ 1870.574106] Oops: 0002 [#1] PREEMPT SMP
    >> >
    >> > This is a regression introduced by commit 0499680a, kernel should
    >> > return -ESRCH if get_proc_task() failed.
    >>
    >> Nice catch!
    >>
    >> However since this error is returned to userspace, shouldn't this be
    >> -ENOENT instead?
    >
    > Failed get_proc_task() frequently results in -ESRCH.  And less
    > frequently results in -ENOENT.
    >
    > It seems odd that inode_operations.permission() would ever return
    > anything other than zero or -EPERM.

    Right, but won't this show up at ESRCH from open(2)? If this is used
    as-is, we just need to have the manpages updated.

    -Kees

    --
    Kees Cook
    ChromeOS Security
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