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This test is a minimalized version of the reproducer given by syzbot (cf. [1]). After introducing CLOSE_RANGE_CLOEXEC syzbot reported a crash when CLOSE_RANGE_CLOEXEC is specified in conjunction with CLOSE_RANGE_UNSHARE. When CLOSE_RANGE_UNSHARE is specified the caller will receive a private file descriptor table in case their file descriptor table is currently shared. For the case where the caller has requested all file descriptors to be actually closed via e.g. close_range(3, ~0U, 0) the kernel knows that the caller does not need any of the file descriptors anymore and will optimize the close operation by only copying all files in the range from 0 to 3 and no others. However, if the caller requested CLOSE_RANGE_CLOEXEC together with CLOSE_RANGE_UNSHARE the caller wants to still make use of the file descriptors so the kernel needs to copy all of them and can't optimize. The original patch didn't account for this and thus could cause oopses as evidenced by the syzbot report. Add tests for this regression. We first create a huge gap in the fd table. When we now call CLOSE_RANGE_UNSHARE with a shared fd table and and with ~0U as upper bound the kernel will only copy up to fd1 file descriptors into the new fd table. If the kernel is buggy and doesn't handle CLOSE_RANGE_CLOEXEC correctly it will not have copied all file descriptors and we will oops! This test passes on a fixed kernel and will trigger an oops on a buggy kernel. [1]: https://syzkaller.appspot.com/text?tag=KernelConfig&x=db720fe37a6a41d8 Cc: Giuseppe Scrivano <gscrivan@redhat.com> Cc: linux-fsdevel@vger.kernel.org Link: syzbot+96cfd2b22b3213646a93@syzkaller.appspotmail.com Link: https://lore.kernel.org/r/20201218145415.801063-4-christian.brauner@ubuntu.com Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> |
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