fs: move fiemap range validation into the file systems instances

Replace fiemap_check_flags with a fiemap_prep helper that also takes the
inode and mapped range, and performs the sanity check and truncation
previously done in fiemap_check_range.  This way the validation is inside
the file system itself and thus properly works for the stacked overlayfs
case as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Link: https://lore.kernel.org/r/20200523073016.2944131-7-hch@lst.de
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Documentation/filesystems/fiemap.txt

@@ -203,16 +203,18 @@ EINTR once fatal signal received.
 
 
 Flag checking should be done at the beginning of the ->fiemap callback via the
-fiemap_check_flags() helper:
+fiemap_prep() helper:
 
-int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags);
+int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
+		u64 start, u64 *len, u32 supported_flags);
 
 The struct fieinfo should be passed in as received from ioctl_fiemap(). The
 set of fiemap flags which the fs understands should be passed via fs_flags. If
-fiemap_check_flags finds invalid user flags, it will place the bad values in
+fiemap_prep finds invalid user flags, it will place the bad values in
 fieinfo->fi_flags and return -EBADR. If the file system gets -EBADR, from
-fiemap_check_flags(), it should immediately exit, returning that error back to
-ioctl_fiemap().
+fiemap_prep(), it should immediately exit, returning that error back to
+ioctl_fiemap().  Additionally the range is validate against the supported
+maximum file size.
 
 
 For each extent in the request range, the file system should call

fs/btrfs/inode.c

@@ -8250,7 +8250,7 @@ static int btrfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 {
 	int	ret;
 
-	ret = fiemap_check_flags(fieinfo, BTRFS_FIEMAP_FLAGS);
+	ret = fiemap_prep(inode, fieinfo, start, &len, BTRFS_FIEMAP_FLAGS);
 	if (ret)
 		return ret;
 

fs/cifs/smb2ops.c

@@ -3408,8 +3408,10 @@ static int smb3_fiemap(struct cifs_tcon *tcon,
 	int i, num, rc, flags, last_blob;
 	u64 next;
 
-	if (fiemap_check_flags(fei, FIEMAP_FLAG_SYNC))
-		return -EBADR;
+	rc = fiemap_prep(d_inode(cfile->dentry), fei, start, &len,
+			FIEMAP_FLAG_SYNC);
+	if (rc)
+		return rc;
 
 	xid = get_xid();
  again:

fs/ext4/extents.c

@@ -4938,8 +4938,9 @@ int ext4_get_es_cache(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		fieinfo->fi_flags &= ~FIEMAP_FLAG_CACHE;
 	}
 
-	if (fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC))
-		return -EBADR;
+	error = fiemap_prep(inode, fieinfo, start, &len, FIEMAP_FLAG_SYNC);
+	if (error)
+		return error;
 
 	error = ext4_fiemap_check_ranges(inode, start, &len);
 	if (error)

fs/f2fs/data.c

@@ -1825,7 +1825,8 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			return ret;
 	}
 
-	ret = fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR);
+	ret = fiemap_prep(inode, fieinfo, start, &len,
+			FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR);
 	if (ret)
 		return ret;
 

fs/ioctl.c

@@ -149,61 +149,50 @@ int fiemap_fill_next_extent(struct fiemap_extent_info *fieinfo, u64 logical,
 EXPORT_SYMBOL(fiemap_fill_next_extent);
 
 /**
- * fiemap_check_flags - check validity of requested flags for fiemap
+ * fiemap_prep - check validity of requested flags for fiemap
+ * @inode:	Inode to operate on
  * @fieinfo:	Fiemap context passed into ->fiemap
- * @fs_flags:	Set of fiemap flags that the file system understands
+ * @start:	Start of the mapped range
+ * @len:	Length of the mapped range, can be truncated by this function.
+ * @supported_flags:	Set of fiemap flags that the file system understands
  *
- * Called from file system ->fiemap callback. This will compute the
- * intersection of valid fiemap flags and those that the fs supports. That
- * value is then compared against the user supplied flags. In case of bad user
- * flags, the invalid values will be written into the fieinfo structure, and
- * -EBADR is returned, which tells ioctl_fiemap() to return those values to
- * userspace. For this reason, a return code of -EBADR should be preserved.
+ * This function must be called from each ->fiemap instance to validate the
+ * fiemap request against the file system parameters.
  *
- * Returns 0 on success, -EBADR on bad flags.
+ * Returns 0 on success, or a negative error on failure.
  */
-int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags)
+int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
+		u64 start, u64 *len, u32 supported_flags)
 {
+	u64 maxbytes = inode->i_sb->s_maxbytes;
 	u32 incompat_flags;
 
-	incompat_flags = fieinfo->fi_flags & ~(FIEMAP_FLAGS_COMPAT & fs_flags);
-	if (incompat_flags) {
-		fieinfo->fi_flags = incompat_flags;
-		return -EBADR;
-	}
-	return 0;
-}
-EXPORT_SYMBOL(fiemap_check_flags);
-
-static int fiemap_check_ranges(struct super_block *sb,
-			       u64 start, u64 len, u64 *new_len)
-{
-	u64 maxbytes = (u64) sb->s_maxbytes;
-
-	*new_len = len;
-
-	if (len == 0)
+	if (*len == 0)
 		return -EINVAL;
-
 	if (start > maxbytes)
 		return -EFBIG;
 
 	/*
 	 * Shrink request scope to what the fs can actually handle.
 	 */
-	if (len > maxbytes || (maxbytes - len) < start)
-		*new_len = maxbytes - start;
+	if (*len > maxbytes || (maxbytes - *len) < start)
+		*len = maxbytes - start;
 
+	supported_flags &= FIEMAP_FLAGS_COMPAT;
+	incompat_flags = fieinfo->fi_flags & ~supported_flags;
+	if (incompat_flags) {
+		fieinfo->fi_flags = incompat_flags;
+		return -EBADR;
+	}
 	return 0;
 }
+EXPORT_SYMBOL(fiemap_prep);
 
 static int ioctl_fiemap(struct file *filp, struct fiemap __user *ufiemap)
 {
 	struct fiemap fiemap;
 	struct fiemap_extent_info fieinfo = { 0, };
 	struct inode *inode = file_inode(filp);
-	struct super_block *sb = inode->i_sb;
-	u64 len;
 	int error;
 
 	if (!inode->i_op->fiemap)
@@ -215,11 +204,6 @@ static int ioctl_fiemap(struct file *filp, struct fiemap __user *ufiemap)
 	if (fiemap.fm_extent_count > FIEMAP_MAX_EXTENTS)
 		return -EINVAL;
 
-	error = fiemap_check_ranges(sb, fiemap.fm_start, fiemap.fm_length,
-				    &len);
-	if (error)
-		return error;
-
 	fieinfo.fi_flags = fiemap.fm_flags;
 	fieinfo.fi_extents_max = fiemap.fm_extent_count;
 	fieinfo.fi_extents_start = ufiemap->fm_extents;
@@ -232,7 +216,8 @@ static int ioctl_fiemap(struct file *filp, struct fiemap __user *ufiemap)
 	if (fieinfo.fi_flags & FIEMAP_FLAG_SYNC)
 		filemap_write_and_wait(inode->i_mapping);
 
-	error = inode->i_op->fiemap(inode, &fieinfo, fiemap.fm_start, len);
+	error = inode->i_op->fiemap(inode, &fieinfo, fiemap.fm_start,
+			fiemap.fm_length);
 	fiemap.fm_flags = fieinfo.fi_flags;
 	fiemap.fm_mapped_extents = fieinfo.fi_extents_mapped;
 	if (copy_to_user(ufiemap, &fiemap, sizeof(fiemap)))
@@ -320,7 +305,7 @@ static int __generic_block_fiemap(struct inode *inode,
 	bool past_eof = false, whole_file = false;
 	int ret = 0;
 
-	ret = fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC);
+	ret = fiemap_prep(inode, fieinfo, start, &len, FIEMAP_FLAG_SYNC);
 	if (ret)
 		return ret;
 

fs/iomap/fiemap.c

@@ -75,7 +75,7 @@ int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
 	ctx.fi = fi;
 	ctx.prev.type = IOMAP_HOLE;
 
-	ret = fiemap_check_flags(fi, FIEMAP_FLAG_SYNC);
+	ret = fiemap_prep(inode, fi, start, &len, FIEMAP_FLAG_SYNC);
 	if (ret)
 		return ret;
 

fs/nilfs2/inode.c

@@ -1006,7 +1006,7 @@ int nilfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	unsigned int blkbits = inode->i_blkbits;
 	int ret, n;
 
-	ret = fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC);
+	ret = fiemap_prep(inode, fieinfo, start, &len, FIEMAP_FLAG_SYNC);
 	if (ret)
 		return ret;
 

fs/ocfs2/extent_map.c

@@ -746,7 +746,8 @@ int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	struct buffer_head *di_bh = NULL;
 	struct ocfs2_extent_rec rec;
 
-	ret = fiemap_check_flags(fieinfo, OCFS2_FIEMAP_FLAGS);
+	ret = fiemap_prep(inode, fieinfo, map_start, &map_len,
+			OCFS2_FIEMAP_FLAGS);
 	if (ret)
 		return ret;
 

include/linux/fiemap.h

@@ -13,9 +13,10 @@ struct fiemap_extent_info {
 							fiemap_extent array */
 };
 
+int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
+		u64 start, u64 *len, u32 supported_flags);
 int fiemap_fill_next_extent(struct fiemap_extent_info *info, u64 logical,
 			    u64 phys, u64 len, u32 flags);
-int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags);
 
 int generic_block_fiemap(struct inode *inode,
 		struct fiemap_extent_info *fieinfo, u64 start, u64 len,