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

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- 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: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Enzo Matsumiya 2026-04-13 16:07:08 -03:00 committed by Steve French
parent 4c221711b2
commit 20d4f9efe0
1 changed files with 10 additions and 7 deletions
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17
fs/smb/client/compress/lz77.c
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@ -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);