| Subject | Re: [PATCH 15/18] vfs, fdtable: prevent bounds-check bypass via speculative execution | From | Sergei Shtylyov <> | Date | Sat, 6 Jan 2018 13:05:40 +0300 |
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On 1/6/2018 4:11 AM, Dan Williams wrote:
> Expectedly, static analysis reports that 'fd' is a user controlled value > that is used as a data dependency to read from the 'fdt->fd' array. In > order to avoid potential leaks of kernel memory values, block > speculative execution of the instruction stream that could issue reads > based on an invalid 'file *' returned from __fcheck_files. > > Based on an original patch by Elena Reshetova. > > Cc: Al Viro <viro@zeniv.linux.org.uk> > Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > --- > include/linux/fdtable.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h > index 1c65817673db..4a147c5c2533 100644 > --- a/include/linux/fdtable.h > +++ b/include/linux/fdtable.h > @@ -81,9 +81,10 @@ struct dentry; > static inline struct file *__fcheck_files(struct files_struct *files, unsigned int fd) > { > struct fdtable *fdt = rcu_dereference_raw(files->fdt); > + struct file __rcu **fdp; > > - if (fd < fdt->max_fds) > - return rcu_dereference_raw(fdt->fd[fd]); > + if ((fdp = nospec_array_ptr(fdt->fd, fd, fdt->max_fds)))
And here...
> + return rcu_dereference_raw(*fdp); > return NULL; > } >
MMR, Sergei
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