[PATCH] xfs: avoid null *src in memcpy call in xlog_write

Eric Sandeen
2015-10-07T16:33:49Z

The gcc undefined behavior sanitizer caught this; surely
any sane memcpy implementation will no-op if size == 0,
but behavior with a *src of NULL is technically undefined
(declared nonnull), so avoid it here.

We are actually in this situation frequently via
xlog_commit_record(), because:

struct xfs_log_iovec reg = {
.i_addr = NULL,
.i_len = 0,
.i_type = XLOG_REG_TYPE_COMMIT,
};

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 4012523..8897fd1 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -2424,7 +2424,10 @@ xlog_write(

/* copy region */
ASSERT(copy_len >= 0);
- memcpy(ptr, reg->i_addr + copy_off, copy_len);
+ ASSERT(reg->i_addr + copy_off > 0 || copy_len == 0);
+ /* size == 0 is ok, but *src == NULL is undefined */
+ if (reg->i_addr + copy_off)
+ memcpy(ptr, reg->i_addr + copy_off, copy_len);
xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);

copy_len += start_rec_copy + sizeof(xlog_op_header_t);