In the quest to remove all stack VLA usage from the kernel[1], this allocates the maximum size stack buffer. Existing checks already require that blocksize >= NTFS_BLOCK_SIZE and mft_record_size <= PAGE_SIZE, so max_bhs can be at most PAGE_SIZE / NTFS_BLOCK_SIZE. Sanity checks are added for robustness.
[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qpxydaacu1rq...@mail.gmail.com Cc: Anton Altaparmakov <[email protected]> Cc: [email protected] Signed-off-by: Kees Cook <[email protected]> --- fs/ntfs/mft.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/fs/ntfs/mft.c b/fs/ntfs/mft.c index 32c523cf5a2d..fb14d17666c8 100644 --- a/fs/ntfs/mft.c +++ b/fs/ntfs/mft.c @@ -35,6 +35,8 @@ #include "mft.h" #include "ntfs.h" +#define MAX_BHS (PAGE_SIZE / NTFS_BLOCK_SIZE) + /** * map_mft_record_page - map the page in which a specific mft record resides * @ni: ntfs inode whose mft record page to map @@ -469,7 +471,7 @@ int ntfs_sync_mft_mirror(ntfs_volume *vol, const unsigned long mft_no, struct page *page; unsigned int blocksize = vol->sb->s_blocksize; int max_bhs = vol->mft_record_size / blocksize; - struct buffer_head *bhs[max_bhs]; + struct buffer_head *bhs[MAX_BHS]; struct buffer_head *bh, *head; u8 *kmirr; runlist_element *rl; @@ -479,6 +481,8 @@ int ntfs_sync_mft_mirror(ntfs_volume *vol, const unsigned long mft_no, ntfs_debug("Entering for inode 0x%lx.", mft_no); BUG_ON(!max_bhs); + if (WARN_ON(max_bhs > MAX_BHS)) + return -EINVAL; if (unlikely(!vol->mftmirr_ino)) { /* This could happen during umount... */ err = ntfs_sync_mft_mirror_umount(vol, mft_no, m); @@ -674,7 +678,7 @@ int write_mft_record_nolock(ntfs_inode *ni, MFT_RECORD *m, int sync) unsigned int blocksize = vol->sb->s_blocksize; unsigned char blocksize_bits = vol->sb->s_blocksize_bits; int max_bhs = vol->mft_record_size / blocksize; - struct buffer_head *bhs[max_bhs]; + struct buffer_head *bhs[MAX_BHS]; struct buffer_head *bh, *head; runlist_element *rl; unsigned int block_start, block_end, m_start, m_end; @@ -684,6 +688,10 @@ int write_mft_record_nolock(ntfs_inode *ni, MFT_RECORD *m, int sync) BUG_ON(NInoAttr(ni)); BUG_ON(!max_bhs); BUG_ON(!PageLocked(page)); + if (WARN_ON(max_bhs > MAX_BHS)) { + err = -EINVAL; + goto err_out; + } /* * If the ntfs_inode is clean no need to do anything. If it is dirty, * mark it as clean now so that it can be redirtied later on if needed. -- 2.17.1
