strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().
Direct replacement is safe here since return value of -E2BIG
is used to check for truncation instead of sizeof(dest).
[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89
Signed-off-by: Azeem Shaikh <[email protected]>
---
drivers/usb/gadget/function/f_printer.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 28db3e336e7d..10dc7c55c25f 100644
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -1211,8 +1211,8 @@ static ssize_t f_printer_opts_pnp_string_show(struct config_item *item,
if (!opts->pnp_string)
goto unlock;
- result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
- if (result >= PAGE_SIZE) {
+ result = strscpy(page, opts->pnp_string, PAGE_SIZE);
+ if (result == -E2BIG) {
result = PAGE_SIZE;
} else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
page[result++] = '\n';
--
2.41.0.162.gfafddb0af9-goog
On Tue, Jun 13, 2023 at 12:43:41AM +0000, Azeem Shaikh wrote:
> strlcpy() reads the entire source buffer first.
> This read may exceed the destination size limit.
> This is both inefficient and can lead to linear read
> overflows if a source string is not NUL-terminated [1].
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with strscpy().
>
> Direct replacement is safe here since return value of -E2BIG
> is used to check for truncation instead of sizeof(dest).
Perhaps say "PAGE_SIZE" here instead of sizeof(dest)?
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
>
> Signed-off-by: Azeem Shaikh <[email protected]>
> ---
> drivers/usb/gadget/function/f_printer.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
> index 28db3e336e7d..10dc7c55c25f 100644
> --- a/drivers/usb/gadget/function/f_printer.c
> +++ b/drivers/usb/gadget/function/f_printer.c
> @@ -1211,8 +1211,8 @@ static ssize_t f_printer_opts_pnp_string_show(struct config_item *item,
> if (!opts->pnp_string)
> goto unlock;
>
> - result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
> - if (result >= PAGE_SIZE) {
> + result = strscpy(page, opts->pnp_string, PAGE_SIZE);
> + if (result == -E2BIG) {
I think "< 1" might be a better test here.
> result = PAGE_SIZE;
> } else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
> page[result++] = '\n';
> --
> 2.41.0.162.gfafddb0af9-goog
>
>
-Kees
--
Kees Cook
On Tue, Jun 13, 2023 at 3:30 PM Kees Cook <[email protected]> wrote:
>
> On Tue, Jun 13, 2023 at 12:43:41AM +0000, Azeem Shaikh wrote:
> > strlcpy() reads the entire source buffer first.
> > This read may exceed the destination size limit.
> > This is both inefficient and can lead to linear read
> > overflows if a source string is not NUL-terminated [1].
> > In an effort to remove strlcpy() completely [2], replace
> > strlcpy() here with strscpy().
> >
> > Direct replacement is safe here since return value of -E2BIG
> > is used to check for truncation instead of sizeof(dest).
>
> Perhaps say "PAGE_SIZE" here instead of sizeof(dest)?
>
Ack.
> >
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> > [2] https://github.com/KSPP/linux/issues/89
> >
> > Signed-off-by: Azeem Shaikh <[email protected]>
> > ---
> > drivers/usb/gadget/function/f_printer.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
> > index 28db3e336e7d..10dc7c55c25f 100644
> > --- a/drivers/usb/gadget/function/f_printer.c
> > +++ b/drivers/usb/gadget/function/f_printer.c
> > @@ -1211,8 +1211,8 @@ static ssize_t f_printer_opts_pnp_string_show(struct config_item *item,
> > if (!opts->pnp_string)
> > goto unlock;
> >
> > - result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
> > - if (result >= PAGE_SIZE) {
> > + result = strscpy(page, opts->pnp_string, PAGE_SIZE);
> > + if (result == -E2BIG) {
>
> I think "< 1" might be a better test here.
>
Curious, why "< 1" instead of "< 0"?
> > result = PAGE_SIZE;
> > } else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
> > page[result++] = '\n';
> > --
> > 2.41.0.162.gfafddb0af9-goog
> >
> >
>
> -Kees
>
> --
> Kees Cook
On Wed, Jun 14, 2023 at 10:12:14AM -0400, Azeem Shaikh wrote:
> On Tue, Jun 13, 2023 at 3:30 PM Kees Cook <[email protected]> wrote:
> >
> > On Tue, Jun 13, 2023 at 12:43:41AM +0000, Azeem Shaikh wrote:
> [...]
> > > - result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
> > > - if (result >= PAGE_SIZE) {
> > > + result = strscpy(page, opts->pnp_string, PAGE_SIZE);
> > > + if (result == -E2BIG) {
> >
> > I think "< 1" might be a better test here.
>
> Curious, why "< 1" instead of "< 0"?
>
> > > result = PAGE_SIZE;
> > > } else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
It's for this case above where "result" may be used in an array index,
and if it's 0 or less, there will be a negative array index (due to the "-
1"). So, here, it needs to be "< 1" instead of the more traditional "< 0".
--
Kees Cook
On Wed, Jun 14, 2023 at 1:51 PM Kees Cook <[email protected]> wrote:
>
> On Wed, Jun 14, 2023 at 10:12:14AM -0400, Azeem Shaikh wrote:
> > On Tue, Jun 13, 2023 at 3:30 PM Kees Cook <[email protected]> wrote:
> > >
> > > On Tue, Jun 13, 2023 at 12:43:41AM +0000, Azeem Shaikh wrote:
> > [...]
> > > > - result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
> > > > - if (result >= PAGE_SIZE) {
> > > > + result = strscpy(page, opts->pnp_string, PAGE_SIZE);
> > > > + if (result == -E2BIG) {
> > >
> > > I think "< 1" might be a better test here.
> >
> > Curious, why "< 1" instead of "< 0"?
> >
> > > > result = PAGE_SIZE;
> > > > } else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
>
> It's for this case above where "result" may be used in an array index,
> and if it's 0 or less, there will be a negative array index (due to the "-
> 1"). So, here, it needs to be "< 1" instead of the more traditional "< 0".
>
Makes sense. Sent out a v2.