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[PATCH 2/3] create_snapshot(): exit early if the file was empty

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Jan 15, 2018, 12:17 UTC
Message-ID
<02915e24958741927467ed750e9782d02ec40c80.1516017331.git.mhagger@alum.mit.edu>
In-Reply-To
<20180114191416.2368-1-kgybels@infogroep.be>

If the `packed_refs` files is entirely empty (i.e., not even a header line), then `load_contents()` returns 1 even though `snapshot->buf` and `snapshot->eof` both end up set to NULL. In that case, the subsequent processing that `create_snapshot()` does is unnecessary, and also involves computing `NULL - NULL` and `NULL + 0`, which are probably safe in real life but are technically undefined in C.

Sidestep both issues by exiting early if `snapshot->buf` is NULL.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 refs/packed-backend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index f20f05b4df..36796d65f0 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -613,7 +613,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
 	acquire_snapshot(snapshot);
 	snapshot->peeled = PEELED_NONE;
 
-	if (!load_contents(snapshot))
+	if (!load_contents(snapshot) || !snapshot->buf)
 		return snapshot;
 
 	/* If the file has a header line, process it: */

-- 
2.14.2
Previous: Michael HaggertyNext: Michael Haggerty
Message 8 of 33 in “packed_ref_cache: don't use mmap() for small files”
  1. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 13, 2018
  2. Johannes SchindelinJan 13, 2018
  3. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 14, 2018
  4. 0/3 Supplements to "packed_ref_cache: don't use mmap() for small files"Michael Haggerty, Jan 15, 2018
  5. Johannes SchindelinJan 17, 2018
  6. Junio C HamanoJan 17, 2018
  7. 1/3 SQUASH? Mention that `snapshot::buf` can be NULL for empty filesMichael Haggerty, Jan 15, 2018
  8. 2/3 create_snapshot(): exit early if the file was emptyMichael Haggerty, Jan 15, 2018
  9. 3/3 find_reference_location(): don't invoke if `snapshot->buf` is NULLMichael Haggerty, Jan 15, 2018
  10. Jeff KingJan 15, 2018
  11. Kim GybelsJan 15, 2018
  12. Jeff KingJan 15, 2018
  13. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 16, 2018
  14. Jeff KingJan 17, 2018
  15. Michael HaggertyJan 21, 2018
  16. Junio C HamanoJan 22, 2018
  17. Michael HaggertyJan 24, 2018
  18. 0/6 Yet another approach to handling empty snapshotsMichael Haggerty, Jan 24, 2018
  19. Jeff KingJan 24, 2018
  20. Junio C HamanoJan 24, 2018
  21. Johannes SchindelinFeb 15, 2018
  22. 1/6 struct snapshot: store `start` rather than `header_len`Michael Haggerty, Jan 24, 2018
  23. Jeff KingJan 24, 2018
  24. 3/6 find_reference_location(): make function safe for empty snapshotsMichael Haggerty, Jan 24, 2018
  25. Jeff KingJan 24, 2018
  26. Junio C HamanoJan 24, 2018
  27. Jeff KingJan 24, 2018
  28. 2/6 create_snapshot(): use `xmemdupz()` rather than a strbufMichael Haggerty, Jan 24, 2018
  29. 5/6 load_contents(): don't try to mmap an empty fileMichael Haggerty, Jan 24, 2018
  30. 4/6 packed_ref_iterator_begin(): make optimization more generalMichael Haggerty, Jan 24, 2018
  31. Jeff KingJan 24, 2018
  32. 6/6 packed_ref_cache: don't use mmap() for small filesMichael Haggerty, Jan 24, 2018
  33. Junio C HamanoJan 24, 2018

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