[PATCH v2 2/2] fat: Support file modification times

[PATCH v2 2/2] fat: Support file modification times

[David Michael]

This allows comparing file ages on EFI system partitions.

Signed-off-by: David Michael <fedora.dm0@gmail.com>
---

Changes since v1:
  - Added the previous patch to help support exfat
  - Added exfat timestamp conversion + setting
  - Switched to datetime variable name for consistency with the header
  - Switched to tabs-for-alignment for consistency in the file

 grub-core/fs/fat.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/grub-core/fs/fat.c b/grub-core/fs/fat.c
index dc493add2..bacf9e60f 100644
--- a/grub-core/fs/fat.c
+++ b/grub-core/fs/fat.c
@@ -26,6 +26,7 @@
 #include <grub/err.h>
 #include <grub/dl.h>
 #include <grub/charset.h>
+#include <grub/datetime.h>
 #ifndef MODE_EXFAT
 #include <grub/fat.h>
 #else
@@ -730,6 +731,28 @@ grub_fat_iterate_dir_next (grub_fshelp_node_t node,
   return grub_errno ? : GRUB_ERR_EOF;
 }
 
+static int
+grub_exfat_timestamp (grub_uint32_t field, grub_uint8_t msec, grub_int32_t *nix) {
+  struct grub_datetime datetime = {
+    .year   = (field >> 25) + 1980,
+    .month  = (field & 0x01E00000) >> 21,
+    .day    = (field & 0x001F0000) >> 16,
+    .hour   = (field & 0x0000F800) >> 11,
+    .minute = (field & 0x000007E0) >>  5,
+    .second = (field & 0x0000001F) * 2 + (msec >= 100 ? 1 : 0),
+  };
+
+  /* The conversion below allows seconds=60, so don't trust its validation.  */
+  if ((field & 0x1F) > 29)
+    return 0;
+
+  /* Validate the 10-msec field even though it is rounded down to seconds.  */
+  if (msec > 199)
+    return 0;
+
+  return grub_datetime2unixtime (&datetime, nix);
+}
+
 #else
 
 static grub_err_t
@@ -857,6 +880,24 @@ grub_fat_iterate_dir_next (grub_fshelp_node_t node,
   return grub_errno ? : GRUB_ERR_EOF;
 }
 
+static int
+grub_fat_timestamp (grub_uint16_t time, grub_uint16_t date, grub_int32_t *nix) {
+  struct grub_datetime datetime = {
+    .year   = (date >> 9) + 1980,
+    .month  = (date & 0x01E0) >> 5,
+    .day    = (date & 0x001F),
+    .hour   = (time >> 11),
+    .minute = (time & 0x07E0) >> 5,
+    .second = (time & 0x001F) * 2,
+  };
+
+  /* The conversion below allows seconds=60, so don't trust its validation.  */
+  if ((time & 0x1F) > 29)
+    return 0;
+
+  return grub_datetime2unixtime (&datetime, nix);
+}
+
 #endif
 
 static grub_err_t lookup_file (grub_fshelp_node_t node,
@@ -966,9 +1007,15 @@ grub_fat_dir (grub_device_t device, const char *path, grub_fs_dir_hook_t hook,
 #ifdef MODE_EXFAT
       if (!ctxt.dir.have_stream)
 	continue;
+      info.mtimeset = grub_exfat_timestamp (grub_le_to_cpu32 (ctxt.entry.type_specific.file.m_time),
+					    ctxt.entry.type_specific.file.m_time_tenth,
+					    &info.mtime);
 #else
       if (ctxt.dir.attr & GRUB_FAT_ATTR_VOLUME_ID)
 	continue;
+      info.mtimeset = grub_fat_timestamp (grub_le_to_cpu16 (ctxt.dir.w_time),
+					  grub_le_to_cpu16 (ctxt.dir.w_date),
+					  &info.mtime);
 #endif
 
       if (hook (ctxt.filename, &info, hook_data))
-- 
2.21.1

Re: [PATCH v2 2/2] fat: Support file modification times

[Daniel Kiper]

On Tue, Mar 03, 2020 at 02:41:08PM -0500, David Michael wrote:
> This allows comparing file ages on EFI system partitions.
>
> Signed-off-by: David Michael <fedora.dm0@gmail.com>
> ---
>
> Changes since v1:
>   - Added the previous patch to help support exfat
>   - Added exfat timestamp conversion + setting
>   - Switched to datetime variable name for consistency with the header
>   - Switched to tabs-for-alignment for consistency in the file
>
>  grub-core/fs/fat.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
>
> diff --git a/grub-core/fs/fat.c b/grub-core/fs/fat.c
> index dc493add2..bacf9e60f 100644
> --- a/grub-core/fs/fat.c
> +++ b/grub-core/fs/fat.c
> @@ -26,6 +26,7 @@
>  #include <grub/err.h>
>  #include <grub/dl.h>
>  #include <grub/charset.h>
> +#include <grub/datetime.h>
>  #ifndef MODE_EXFAT
>  #include <grub/fat.h>
>  #else
> @@ -730,6 +731,28 @@ grub_fat_iterate_dir_next (grub_fshelp_node_t node,
>    return grub_errno ? : GRUB_ERR_EOF;
>  }
>
> +static int
> +grub_exfat_timestamp (grub_uint32_t field, grub_uint8_t msec, grub_int32_t *nix) {
> +  struct grub_datetime datetime = {
> +    .year   = (field >> 25) + 1980,
> +    .month  = (field & 0x01E00000) >> 21,
> +    .day    = (field & 0x001F0000) >> 16,
> +    .hour   = (field & 0x0000F800) >> 11,
> +    .minute = (field & 0x000007E0) >>  5,
> +    .second = (field & 0x0000001F) * 2 + (msec >= 100 ? 1 : 0),
> +  };
> +
> +  /* The conversion below allows seconds=60, so don't trust its validation.  */

60 seconds is a valid value in case of leap second. Hence, the question
is: Can 60 seconds be represented properly in exFAT somehow? OK, this
does not happen often. So, if we want ignore that case then at least
I would like to have an explanation that we ignore it due to...

> +  if ((field & 0x1F) > 29)
> +    return 0;

You silently ignore this error. Should not you spit something to the
console in this case? Or maybe at least set grub_errno? This way
user will know that result of comparison should not be trusted...

> +  /* Validate the 10-msec field even though it is rounded down to seconds.  */
> +  if (msec > 199)
> +    return 0;

Ditto...

> +  return grub_datetime2unixtime (&datetime, nix);
> +}
> +
>  #else
>
>  static grub_err_t
> @@ -857,6 +880,24 @@ grub_fat_iterate_dir_next (grub_fshelp_node_t node,
>    return grub_errno ? : GRUB_ERR_EOF;
>  }
>
> +static int
> +grub_fat_timestamp (grub_uint16_t time, grub_uint16_t date, grub_int32_t *nix) {
> +  struct grub_datetime datetime = {
> +    .year   = (date >> 9) + 1980,
> +    .month  = (date & 0x01E0) >> 5,
> +    .day    = (date & 0x001F),
> +    .hour   = (time >> 11),
> +    .minute = (time & 0x07E0) >> 5,
> +    .second = (time & 0x001F) * 2,
> +  };
> +
> +  /* The conversion below allows seconds=60, so don't trust its validation.  */
> +  if ((time & 0x1F) > 29)
> +    return 0;

Ditto...

Daniel

Re: [PATCH v2 2/2] fat: Support file modification times

[David Michael]

On Fri, Mar 6, 2020 at 7:19 AM Daniel Kiper <dkiper@net-space.pl> wrote:
> On Tue, Mar 03, 2020 at 02:41:08PM -0500, David Michael wrote:
> > This allows comparing file ages on EFI system partitions.
> >
> > Signed-off-by: David Michael <fedora.dm0@gmail.com>
> > ---
> >
> > Changes since v1:
> >   - Added the previous patch to help support exfat
> >   - Added exfat timestamp conversion + setting
> >   - Switched to datetime variable name for consistency with the header
> >   - Switched to tabs-for-alignment for consistency in the file
> >
> >  grub-core/fs/fat.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 47 insertions(+)
> >
> > diff --git a/grub-core/fs/fat.c b/grub-core/fs/fat.c
> > index dc493add2..bacf9e60f 100644
> > --- a/grub-core/fs/fat.c
> > +++ b/grub-core/fs/fat.c
> > @@ -26,6 +26,7 @@
> >  #include <grub/err.h>
> >  #include <grub/dl.h>
> >  #include <grub/charset.h>
> > +#include <grub/datetime.h>
> >  #ifndef MODE_EXFAT
> >  #include <grub/fat.h>
> >  #else
> > @@ -730,6 +731,28 @@ grub_fat_iterate_dir_next (grub_fshelp_node_t node,
> >    return grub_errno ? : GRUB_ERR_EOF;
> >  }
> >
> > +static int
> > +grub_exfat_timestamp (grub_uint32_t field, grub_uint8_t msec, grub_int32_t *nix) {
> > +  struct grub_datetime datetime = {
> > +    .year   = (field >> 25) + 1980,
> > +    .month  = (field & 0x01E00000) >> 21,
> > +    .day    = (field & 0x001F0000) >> 16,
> > +    .hour   = (field & 0x0000F800) >> 11,
> > +    .minute = (field & 0x000007E0) >>  5,
> > +    .second = (field & 0x0000001F) * 2 + (msec >= 100 ? 1 : 0),
> > +  };
> > +
> > +  /* The conversion below allows seconds=60, so don't trust its validation.  */
>
> 60 seconds is a valid value in case of leap second. Hence, the question
> is: Can 60 seconds be represented properly in exFAT somehow? OK, this
> does not happen often. So, if we want ignore that case then at least
> I would like to have an explanation that we ignore it due to...

I enforced the 0-59 range because that is what is declared valid in
the spec.  See 11.3.5 in ECMA-107[1] and 7.4.8 for exfat[2].

> > +  if ((field & 0x1F) > 29)
> > +    return 0;
>
> You silently ignore this error. Should not you spit something to the
> console in this case? Or maybe at least set grub_errno? This way
> user will know that result of comparison should not be trusted...

The functions also rely on the grub_datetime2unixtime field
validations, which do not print errors.  I can add a general
grub_error if info.mtimeset is zero so it warns of all failures.

Thanks.

David

[1] https://www.ecma-international.org/publications/files/ECMA-ST/Ecma-107.pdf
[2] https://docs.microsoft.com/en-us/windows/win32/fileio/exfat-specification

Re: [PATCH v2 2/2] fat: Support file modification times

[Daniel Kiper]

On Fri, Mar 06, 2020 at 10:48:07AM -0500, David Michael wrote:
> On Fri, Mar 6, 2020 at 7:19 AM Daniel Kiper <dkiper@net-space.pl> wrote:
> > On Tue, Mar 03, 2020 at 02:41:08PM -0500, David Michael wrote:
> > > This allows comparing file ages on EFI system partitions.
> > >
> > > Signed-off-by: David Michael <fedora.dm0@gmail.com>
> > > ---
> > >
> > > Changes since v1:
> > >   - Added the previous patch to help support exfat
> > >   - Added exfat timestamp conversion + setting
> > >   - Switched to datetime variable name for consistency with the header
> > >   - Switched to tabs-for-alignment for consistency in the file
> > >
> > >  grub-core/fs/fat.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 47 insertions(+)
> > >
> > > diff --git a/grub-core/fs/fat.c b/grub-core/fs/fat.c
> > > index dc493add2..bacf9e60f 100644
> > > --- a/grub-core/fs/fat.c
> > > +++ b/grub-core/fs/fat.c
> > > @@ -26,6 +26,7 @@
> > >  #include <grub/err.h>
> > >  #include <grub/dl.h>
> > >  #include <grub/charset.h>
> > > +#include <grub/datetime.h>
> > >  #ifndef MODE_EXFAT
> > >  #include <grub/fat.h>
> > >  #else
> > > @@ -730,6 +731,28 @@ grub_fat_iterate_dir_next (grub_fshelp_node_t node,
> > >    return grub_errno ? : GRUB_ERR_EOF;
> > >  }
> > >
> > > +static int
> > > +grub_exfat_timestamp (grub_uint32_t field, grub_uint8_t msec, grub_int32_t *nix) {
> > > +  struct grub_datetime datetime = {
> > > +    .year   = (field >> 25) + 1980,
> > > +    .month  = (field & 0x01E00000) >> 21,
> > > +    .day    = (field & 0x001F0000) >> 16,
> > > +    .hour   = (field & 0x0000F800) >> 11,
> > > +    .minute = (field & 0x000007E0) >>  5,
> > > +    .second = (field & 0x0000001F) * 2 + (msec >= 100 ? 1 : 0),
> > > +  };
> > > +
> > > +  /* The conversion below allows seconds=60, so don't trust its validation.  */
> >
> > 60 seconds is a valid value in case of leap second. Hence, the question
> > is: Can 60 seconds be represented properly in exFAT somehow? OK, this
> > does not happen often. So, if we want ignore that case then at least
> > I would like to have an explanation that we ignore it due to...
>
> I enforced the 0-59 range because that is what is declared valid in
> the spec.  See 11.3.5 in ECMA-107[1] and 7.4.8 for exfat[2].

OK, could you add references to these documents into the comments?

> > > +  if ((field & 0x1F) > 29)
> > > +    return 0;
> >
> > You silently ignore this error. Should not you spit something to the
> > console in this case? Or maybe at least set grub_errno? This way
> > user will know that result of comparison should not be trusted...
>
> The functions also rely on the grub_datetime2unixtime field
> validations, which do not print errors.  I can add a general
> grub_error if info.mtimeset is zero so it warns of all failures.

Works for me.

Daniel