Messages in this thread | | | Subject | Re: [PATCH v2] kernel/kcov: unproxify debugfs file's fops | From | Sasha Levin <> | Date | Tue, 14 Jun 2016 17:19:13 -0400 |
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On 05/24/2016 10:39 AM, Greg Kroah-Hartman wrote: > On Tue, May 24, 2016 at 02:05:05PM +0200, Nicolai Stange wrote: >> > Since commit 49d200deaa68 ("debugfs: prevent access to removed files' >> > private data"), a debugfs file's file_operations methods get proxied >> > through lifetime aware wrappers. >> > >> > However, only a certain subset of the file_operations members is supported >> > by debugfs and ->mmap isn't among them -- it appears to be NULL from the >> > VFS layer's perspective. >> > >> > This behaviour breaks the /sys/kernel/debug/kcov file introduced >> > concurrently with commit 5c9a8750a640 ("kernel: add kcov code coverage"). >> > >> > Since that file never gets removed, there is no file removal race and thus, >> > a lifetime checking proxy isn't needed. >> > >> > Avoid the proxying for /sys/kernel/debug/kcov by creating it via >> > debugfs_create_file_unsafe() rather than debugfs_create_file(). >> > >> > Fixes: 49d200deaa68 ("debugfs: prevent access to removed files' private >> > data") >> > Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") >> > Signed-off-by: Nicolai Stange <nicstange@gmail.com> >> > --- >> > The v1 thread can be found at >> > http://lkml.kernel.org/g/1464011147-31836-1-git-send-email-nicstange@gmail.com >> > >> > Changes to v1: >> > - Following the suggestion of Kees Cook, a comment explaining why the use >> > of debugfs_create_file_unsafe() is actually safe there has been added. >> > >> > This issue has been debugged and reported by >> > Sasha Levin <sasha.levin@oracle.com>: >> > http://lkml.kernel.org/g/573F4200.3080208@oracle.com >> > >> > Applicable to linux-next 20160524. >> > In particular, it depends on >> > - c64688081490 ("debugfs: add support for self-protecting attribute file >> > fops") >> > - 5c9a8750a640 ("kernel: add kcov code coverage") >> > >> > kernel/kcov.c | 7 ++++++- >> > 1 file changed, 6 insertions(+), 1 deletion(-) >> > >> > diff --git a/kernel/kcov.c b/kernel/kcov.c >> > index a02f2dd..8d44b3f 100644 >> > --- a/kernel/kcov.c >> > +++ b/kernel/kcov.c >> > @@ -264,7 +264,12 @@ static const struct file_operations kcov_fops = { >> > >> > static int __init kcov_init(void) >> > { >> > - if (!debugfs_create_file("kcov", 0600, NULL, NULL, &kcov_fops)) { >> > + /* >> > + * The kcov debugfs file won't ever get removed and thus, >> > + * there is no need to protect it against removal races. The >> > + * use of debugfs_create_file_unsafe() is actually safe here. >> > + */ >> > + if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) { >> > pr_err("failed to create kcov in debugfs\n"); >> > return -ENOMEM; >> > } > Thanks, I'll queue this up after 4.7-rc1 is out.
Hey Greg,
Just wanted to remind you about this one.
Thanks, Sasha
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