Re: [PATCH v4 6/8] dir: fix checks on common prefix directory

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> Please use st_add3() while you are at it.
>
> I'd also usually suggest FLEX_ALLOC_MEM() for even more simplicity, but
> it looks like filling the string is handled separately (and done many
> times).
>
> I have to wonder, though, if it wouldn't be simpler to move away from
> "struct dirent" here (and it looks like Junio suggested the same earlier
> in the thread). I don't know this code very well, but it looks
> like it could easily get by passing around a name pointer and a dtype
> through the cached_dir. The patch below seems like it's not too bad a
> cleanup, but possibly the names could be better.

It does look like a good clean-up.

In the meantime, here is to apologize for merging the patch a bit
too early to 'next'.

-- >8 --
From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 20 Dec 2019 09:55:53 -0800
Subject: [PATCH] dir.c: use st_add3() for allocation size

When preparing a manufactured dirent instance, we add a length of
path to the size of struct to decide how many bytes to allocate.
Make sure this addition does not wrap-around to cause us
underallocate.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dir.c b/dir.c
index e1b74f6478..113170aeb9 100644
--- a/dir.c
+++ b/dir.c
@@ -2154,7 +2154,7 @@ static int treat_leading_path(struct dir_struct *dir,
 	 * For either case, padding with len+1 bytes at the end will ensure
 	 * sufficient storage space.
 	 */
-	de = xcalloc(1, sizeof(struct dirent)+len+1);
+	de = xcalloc(1, st_add3(sizeof(struct dirent), len, 1));
 	memset(&cdir, 0, sizeof(cdir));
 	cdir.de = de;
 #if defined(DT_UNKNOWN) && !defined(NO_D_TYPE_IN_DIRENT)
-- 
2.24.1-769-g187e15c71d