Messages in this thread | | | Date | Thu, 14 Apr 2016 15:46:00 -0700 | Subject | Re: [RFC PATCH] fs: define a string representation of the kernel_read_file_id enumeration | From | Kees Cook <> |
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On Thu, Apr 14, 2016 at 1:49 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote: > (This patch is being posted as an RFC and has not been compiled.) > > A string representation of the kernel_read_file_id enumeration is needed > for displaying messages (eg. pr_info, auditing). We assume that the > string representation of the enumeration will be needed by multiple LSMs > and the integrity subsystem. Instead of each defining their own string > representation, this patch defines a common one. > > Each time a new enumeration entry is defined, it will need to be reflected > in the list of strings. To simplify keeping the list of strings in sync > with the enumeration, this patch proposes using two preprocessing > macros: stringify_1 and an a new macro named enumify. > > In general, preprocessing macros are not recommended. The question is > whether using preprocessing macros is preferable to having to remember to > update the list each time a new enumeration is defined. > > With these changes, the simplified version of kernel_read_file_id_str() > could be moved to a header. > > Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com> > --- > fs/exec.c | 28 ++++++++++++++-------------- > include/linux/fs.h | 17 +++++++++++------ > 2 files changed, 25 insertions(+), 20 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index 05e71b6..e9b9b85 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -819,25 +819,25 @@ struct file *open_exec(const char *name) > } > EXPORT_SYMBOL(open_exec); > > +static char *kernel_read_file_str[READING_MAX_ID]; > const char *kernel_read_file_id_str(enum kernel_read_file_id id) > { > - switch (id) { > - case READING_FIRMWARE: > - return "firmware"; > - case READING_MODULE: > - return "kernel-module"; > - case READING_KEXEC_IMAGE: > - return "kexec-image"; > - case READING_KEXEC_INITRAMFS: > - return "kexec-initramfs"; > - case READING_POLICY: > - return "security-policy"; > - default: > - return "unknown"; > - } > + return kernel_read_file_str[id];
(Whatever is decided, I'd still prefer an explicit bounds-check on the "id" argument here.)
-Kees
> } > EXPORT_SYMBOL(kernel_read_file_id_str); > > +void __init kernel_read_file_init() > +{ > + const char *kernel_read_file_upper_str[] = { > + __kernel_read_file_id(__stringify_1) > + }; > + > + for (i = 0; i < READING_MAX_ID; i++) { > + kernel_read_file_str[i] = strdup(kernel_read_file_upper_str[i]; > + lower_case(kernel_read_file_str[i]; > + } > +} > + > int kernel_read(struct file *file, loff_t offset, > char *addr, unsigned long count) > { > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 23ea886..35ed80f 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2580,13 +2580,18 @@ static inline void i_readcount_inc(struct inode *inode) > #endif > extern int do_pipe_flags(int *, int); > > +#define __kernel_read_file_id(id) \ > + id(UNKNOWN) \ > + id(FIRMWARE) \ > + id(MODULE) \ > + id(KEXEC_IMAGE) \ > + id(KEXEC_INITRAMFS) \ > + id(POLICY) \ > + id(MAX_ID) \ > +#define __enumify(ENUM) READING_ ## ENUM, > + > enum kernel_read_file_id { > - READING_FIRMWARE = 1, > - READING_MODULE, > - READING_KEXEC_IMAGE, > - READING_KEXEC_INITRAMFS, > - READING_POLICY, > - READING_MAX_ID > + __kernel_read_file_id(__enumify) > }; > > extern const char *kernel_read_file_id_str(enum kernel_read_file_id id); > -- > 2.1.0 >
-- Kees Cook Chrome OS & Brillo Security
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