From: Enzo Matsumiya <ematsumiya@suse.de>
To: linux-cifs@vger.kernel.org
Cc: smfrench@gmail.com, pc@manguebit.com, ronniesahlberg@gmail.com,
sprasad@microsoft.com, tom@talpey.com, bharathsm@microsoft.com,
henrique.carvalho@suse.com
Subject: [PATCH 3/8] smb: client: compress: fix counting in LZ77 match finding
Date: Mon, 13 Apr 2026 16:07:08 -0300 [thread overview]
Message-ID: <20260413190713.283939-3-ematsumiya@suse.de> (raw)
In-Reply-To: <20260413190713.283939-1-ematsumiya@suse.de>
- 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>
---
fs/smb/client/compress/lz77.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/fs/smb/client/compress/lz77.c b/fs/smb/client/compress/lz77.c
index c1e7fada6e61..61cdf1c14612 100644
--- a/fs/smb/client/compress/lz77.c
+++ b/fs/smb/client/compress/lz77.c
@@ -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);
--
2.53.0
next prev parent reply other threads:[~2026-04-13 19:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-13 19:07 [PATCH 1/8] smb: client: compress: fix buffer overrun in lz77_compress() Enzo Matsumiya
2026-04-13 19:07 ` [PATCH 2/8] smb: client: compress: fix bad encoding on last LZ77 flag Enzo Matsumiya
2026-04-19 1:35 ` Steve French
2026-04-13 19:07 ` Enzo Matsumiya [this message]
2026-04-13 19:07 ` [PATCH 4/8] smb: client: compress: increase LZ77_MATCH_MAX_DIST Enzo Matsumiya
2026-04-13 19:07 ` [PATCH 5/8] smb: client: compress: LZ77 optimizations Enzo Matsumiya
2026-04-13 19:07 ` [PATCH 6/8] smb: client: compress: add code docs to lz77.c Enzo Matsumiya
2026-04-13 19:07 ` [PATCH 7/8] smb: client: compress: add compress/common.h Enzo Matsumiya
2026-04-20 21:24 ` Nathan Chancellor
2026-04-20 21:31 ` Steve French
2026-04-13 19:07 ` [PATCH 8/8] smb: common: add SMB3_COMPRESS_MAX_ALGS Enzo Matsumiya
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