Commit 20d4f9ef authored by Enzo Matsumiya's avatar Enzo Matsumiya Committed by Steve French
Browse files

smb: client: compress: fix counting in LZ77 match finding 



- lz77_match_len() increments @cur before checking for equality,
  leading to off-by-one match len in some cases.

  Fix by moving pointers increment to inside the loop.
  Also rename @wnd arg to @match (more accurate name).
- both lz77_match_len() and lz77_compress() checked for
  "buf + step < end" when the correct is "<=" for such cases.

Signed-off-by: default avatarEnzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
parent 4c221711

fs/smb/client/compress/lz77.c

+10 −7
Original line number Diff line number Diff line
@@ -48,17 +48,17 @@ static __always_inline void lz77_write32(u32 *ptr, u32 v) 
	put_unaligned_le32(v, ptr);

}



static __always_inline u32 lz77_match_len(const void *wnd, const void *cur, const void *end)

static __always_inline u32 lz77_match_len(const void *match, const void *cur, const void *end)

{

	const void *start = cur;

	u64 diff;



	/* Safe for a do/while because otherwise we wouldn't reach here from the main loop. */

	do {

		diff = lz77_read64(cur) ^ lz77_read64(wnd);

		diff = lz77_read64(cur) ^ lz77_read64(match);

		if (!diff) {

			cur += LZ77_STEP_SIZE;

			wnd += LZ77_STEP_SIZE;

			match += LZ77_STEP_SIZE;



			continue;

		}
@@ -67,10 +67,13 @@ static __always_inline u32 lz77_match_len(const void *wnd, const void *cur, cons 
		cur += count_trailing_zeros(diff) >> 3;



		return (cur - start);

	} while (likely(cur + LZ77_STEP_SIZE < end));

	} while (likely(cur + LZ77_STEP_SIZE <= end));



	while (cur < end && lz77_read8(cur++) == lz77_read8(wnd++))

		;

	/* Fallback to byte-by-byte comparison for last <8 bytes. */

	while (cur < end && lz77_read8(cur) == lz77_read8(match)) {

		cur++;

		match++;

	}



	return (cur - start);

}
@@ -195,7 +198,7 @@ noinline int lz77_compress(const void *src, u32 slen, void *dst, u32 *dlen) 
			flag_pos = dstp;

			dstp += 4;

		}

	} while (likely(srcp + LZ77_STEP_SIZE < end));

	} while (likely(srcp + LZ77_STEP_SIZE <= end));



	while (srcp < end) {

		u32 c = umin(end - srcp, 32 - flag_count);