| Message ID | 20240123002814.1396804-53-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | overflow: Refactor open-coded arithmetic wrap-around | expand |
On Mon 22-01-24 16:27:28, Kees Cook wrote: > In an effort to separate intentional arithmetic wrap-around from > unexpected wrap-around, we need to refactor places that depend on this > kind of math. One of the most common code patterns of this is: > > VAR + value < VAR > > Notably, this is considered "undefined behavior" for signed and pointer > types, which the kernel works around by using the -fno-strict-overflow > option in the build[1] (which used to just be -fwrapv). Regardless, we > want to get the kernel source to the position where we can meaningfully > instrument arithmetic wrap-around conditions and catch them when they > are unexpected, regardless of whether they are signed[2], unsigned[3], > or pointer[4] types. > > Refactor open-coded wrap-around addition test to use add_would_overflow(). > This paves the way to enabling the wrap-around sanitizers in the future. > > Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] > Link: https://github.com/KSPP/linux/issues/26 [2] > Link: https://github.com/KSPP/linux/issues/27 [3] > Link: https://github.com/KSPP/linux/issues/344 [4] > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: Christian Brauner <brauner@kernel.org> > Cc: Jan Kara <jack@suse.cz> > Cc: linux-fsdevel@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> Looks good atlhough I'd prefer wrapping the line to not overflow 80 chars. Anyway feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > fs/remap_range.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/remap_range.c b/fs/remap_range.c > index f8c1120b8311..15e91bf2c5e3 100644 > --- a/fs/remap_range.c > +++ b/fs/remap_range.c > @@ -45,7 +45,7 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in, > return -EINVAL; > > /* Ensure offsets don't wrap. */ > - if (pos_in + count < pos_in || pos_out + count < pos_out) > + if (add_would_overflow(pos_in, count) || add_would_overflow(pos_out, count)) > return -EINVAL; > > size_in = i_size_read(inode_in); > -- > 2.34.1 >
diff --git a/fs/remap_range.c b/fs/remap_range.c index f8c1120b8311..15e91bf2c5e3 100644 --- a/fs/remap_range.c +++ b/fs/remap_range.c @@ -45,7 +45,7 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in, return -EINVAL; /* Ensure offsets don't wrap. */ - if (pos_in + count < pos_in || pos_out + count < pos_out) + if (add_would_overflow(pos_in, count) || add_would_overflow(pos_out, count)) return -EINVAL; size_in = i_size_read(inode_in);
In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded wrap-around addition test to use add_would_overflow(). This paves the way to enabling the wrap-around sanitizers in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- fs/remap_range.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)