| Message ID | 20240123002814.1396804-19-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 16:26:54, 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 unsigned wrap-around addition test to use > check_add_overflow(), retaining the result for later usage (which removes > the redundant open-coded addition). 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. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > fs/read_write.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/fs/read_write.c b/fs/read_write.c > index d4c036e82b6c..e24b94a8937d 100644 > --- a/fs/read_write.c > +++ b/fs/read_write.c > @@ -1417,6 +1417,7 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, > struct inode *inode_out = file_inode(file_out); > uint64_t count = *req_count; > loff_t size_in; > + loff_t sum_in, sum_out; > int ret; > > ret = generic_file_rw_checks(file_in, file_out); > @@ -1451,7 +1452,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, > return -ETXTBSY; > > /* Ensure offsets don't wrap. */ > - if (pos_in + count < pos_in || pos_out + count < pos_out) > + if (check_add_overflow(pos_in, count, &sum_in) || > + check_add_overflow(pos_out, count, &sum_out)) > return -EOVERFLOW; > > /* Shorten the copy to EOF */ > @@ -1467,8 +1469,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, > > /* Don't allow overlapped copying within the same file. */ > if (inode_in == inode_out && > - pos_out + count > pos_in && > - pos_out < pos_in + count) > + sum_out > pos_in && > + pos_out < sum_in) > return -EINVAL; > > *req_count = count; > -- > 2.34.1 >
diff --git a/fs/read_write.c b/fs/read_write.c index d4c036e82b6c..e24b94a8937d 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -1417,6 +1417,7 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, struct inode *inode_out = file_inode(file_out); uint64_t count = *req_count; loff_t size_in; + loff_t sum_in, sum_out; int ret; ret = generic_file_rw_checks(file_in, file_out); @@ -1451,7 +1452,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, return -ETXTBSY; /* Ensure offsets don't wrap. */ - if (pos_in + count < pos_in || pos_out + count < pos_out) + if (check_add_overflow(pos_in, count, &sum_in) || + check_add_overflow(pos_out, count, &sum_out)) return -EOVERFLOW; /* Shorten the copy to EOF */ @@ -1467,8 +1469,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, /* Don't allow overlapped copying within the same file. */ if (inode_in == inode_out && - pos_out + count > pos_in && - pos_out < pos_in + count) + sum_out > pos_in && + pos_out < sum_in) return -EINVAL; *req_count = count;
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 unsigned wrap-around addition test to use check_add_overflow(), retaining the result for later usage (which removes the redundant open-coded addition). 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/read_write.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)