Change #254364

Comments

copy: protect against infinite loop due to pathological race
Consider:

1. In infer_scantype():
    - SEEK_DATA returns 0
      - hole punched at 0
    - SEEK_HOLE returns 0 (now a hole)
    - Cache scan_inference->hole_start = 0
2. In lseek_copy():
      - data written at 0
    - ext_start = 0, use cached hole_start = 0
    - ext_len = 0
    - now loop doesn't progress

* src/copy-file-data.c (lseek_copy): Apply a more defensive check
to ensure we only use the cached offsets in SCAN_INFERENCE once.
This protects against an infinite loop where an extent (at SRC_POS)
flip flops between data and hole extent while infer_scantype()
and lseek_copy() are inspecting it.  I.e. ensure we use SEEK_HOLE
to progress the copy.

Changed files

• src/copy-file-data.c