How about this instead?
--D
---
From: Eric Biggers <ebiggers@xxxxxxxxxx>
During the "insert range" fallocate operation, i_size grows by the
specified 'len' bytes. XFS verifies that i_size + len < s_maxbytes, as
it should. But this comparison is done using the signed 'loff_t', and
'i_size + len' can wrap around to a negative value, causing the check to
incorrectly pass, resulting in an inode with "negative" i_size. This is
possible on 64-bit platforms, where XFS sets s_maxbytes = LLONG_MAX.
ext4 and f2fs don't run into this because they set a smaller s_maxbytes.
Fix it by doing an unsigned comparison instead.
Reproducer:
xfs_io -f file -c "truncate $(((1<<63)-1))" -c "finsert 0 4096"
Fixes: a904b1ca5751 ("xfs: Add support FALLOC_FL_INSERT_RANGE for fallocate")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.1+
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
[darrick: rearrange this whole function to use subtraction to avoid
overflow of the signed integer addition]
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
fs/xfs/xfs_file.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 9fd9dd7..a385334 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -779,21 +779,27 @@ xfs_file_fallocate(
goto out_unlock;
} else if (mode & FALLOC_FL_INSERT_RANGE) {
unsigned int blksize_mask = i_blocksize(inode) - 1;
+ loff_t isize;
- new_size = i_size_read(inode) + len;
- if (offset & blksize_mask || len & blksize_mask) {
- error = -EINVAL;
+ isize = i_size_read(inode);
+
+ /*
+ * New inode size must not exceed ->s_maxbytes, accounting for
+ * possible signed overflow.
+ */
+ if (inode->i_sb->s_maxbytes - isize < len) {
+ error = -EFBIG;
goto out_unlock;
}
- /* check the new inode size does not wrap through zero */
- if (new_size > inode->i_sb->s_maxbytes) {
- error = -EFBIG;
+ if (offset & blksize_mask || len & blksize_mask) {
+ error = -EINVAL;
goto out_unlock;
}
+ new_size = isize + len;
/* Offset should be less than i_size */
- if (offset >= i_size_read(inode)) {
+ if (offset >= isize) {
error = -EINVAL;
goto out_unlock;
}
--
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