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: "Theodore Ts'o" <tytso@xxxxxxx> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx> Cc: linux-ext4@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- fs/ext4/block_validity.c | 2 +- fs/ext4/resize.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c index 6fe3c941b565..85f859979d2f 100644 --- a/fs/ext4/block_validity.c +++ b/fs/ext4/block_validity.c @@ -302,7 +302,7 @@ int ext4_sb_block_valid(struct super_block *sb, struct inode *inode, int ret = 1; if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) || - (start_blk + count < start_blk) || + (add_would_overflow(start_blk, count)) || (start_blk + count > ext4_blocks_count(sbi->s_es))) return 0; diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 4d4a5a32e310..fb8d3745d031 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1871,7 +1871,7 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es, add = EXT4_BLOCKS_PER_GROUP(sb) - last; - if (o_blocks_count + add < o_blocks_count) { + if (add_would_overflow(o_blocks_count, add)) { ext4_warning(sb, "blocks_count overflow"); return -EINVAL; } -- 2.34.1
