proc: fix NULL dereference when reading /proc/<pid>/auxv
Reading auxv of any kernel thread results in NULL pointer dereferencing in auxv_read() where mm can be NULL. Fix that by checking for NULL mm and bailing out early. This is also the original behavior changed by recent commit c5317167 ("proc: switch auxv to use of __mem_open()"). # cat /proc/2/auxv Unable to handle kernel NULL pointer dereference at virtual address 000000a8 Internal error: Oops: 17 [#1] PREEMPT SMP ARM CPU: 3 PID: 113 Comm: cat Not tainted 4.9.0-rc1-ARCH+ #1 Hardware name: BCM2709 task: ea3b0b00 task.stack: e99b2000 PC is at auxv_read+0x24/0x4c LR is at do_readv_writev+0x2fc/0x37c Process cat (pid: 113, stack limit = 0xe99b2210) Call chain: auxv_read do_readv_writev vfs_readv default_file_splice_read splice_direct_to_actor do_splice_direct do_sendfile SyS_sendfile64 ret_fast_syscall Fixes: c5317167 ("proc: switch auxv to use of __mem_open()") Link: http://lkml.kernel.org/r/1476966200-14457-1-git-send-email-chianglungyu@gmail.comSigned-off-by: NLeon Yu <chianglungyu@gmail.com> Acked-by: NOleg Nesterov <oleg@redhat.com> Acked-by: NMichal Hocko <mhocko@suse.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Kees Cook <keescook@chromium.org> Cc: John Stultz <john.stultz@linaro.org> Cc: Mateusz Guzik <mguzik@redhat.com> Cc: Janis Danisevskis <jdanis@google.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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