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Fri, 10 Jul 2026 13:37:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id oHGQCq31UGo0FQAAD6G6ig (envelope-from ); Fri, 10 Jul 2026 13:37:49 +0000 Date: Fri, 10 Jul 2026 10:37:39 -0300 From: Enzo Matsumiya To: Laxman Acharya Padhya Cc: Steve French , Namjae Jeon , Steve French , Namjae Jeon , linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] smb: common: fix undefined shifts in LZ77 flag encoding Message-ID: References: <20260709173019.36808-1-acharyalaxman8848@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260709173019.36808-1-acharyalaxman8848@gmail.com> X-Spam-Flag: NO X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MISSING_XM_UA(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[gmail.com]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[samba.org,kernel.org,gmail.com,vger.kernel.org,lists.samba.org]; RCPT_COUNT_SEVEN(0.00)[9]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,imap1.dmz-prg2.suse.org:helo] X-Spam-Level: X-Spam-Score: -4.30 Hi, Thanks for the patch. On 07/09, Laxman Acharya Padhya wrote: >The LZ77 encoder emits flags in 32-bit words, but keeps the >accumulator in a long and can shift it by 32 bits. > >This happens when lz77_encode_literals() emits a full all-literal flag >word, and again when smb_lz77_compress() pads an empty final flag word. >On 32-bit builds SMB2 compression code is supposed to be supported on 64-bit (and little endian) architectures only. I was going to send a patch to make such checks at build-time (to make that an explicit "statement"), but I'm waiting for Steve's input on it. Cheers, Enzo >these shift counts are equal to the width of the >shifted type, so UBSAN can report a runtime error and the encoded flag >word is undefined. > >Use a u32 accumulator and special-case the full-word states so the same >flag words are emitted without issuing 32-bit shifts. > >Fixes: d14bbfff259c ("smb3: mark compression as CONFIG_EXPERIMENTAL and fix missing compression operation") >Cc: stable@vger.kernel.org >Assisted-by: Codex:gpt-5 >Signed-off-by: Laxman Acharya Padhya >--- > fs/smb/common/compress/lz77.c | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > >diff --git a/fs/smb/common/compress/lz77.c b/fs/smb/common/compress/lz77.c >index 9216d973d87..be6853ad576 100644 >--- a/fs/smb/common/compress/lz77.c >+++ b/fs/smb/common/compress/lz77.c >@@ -188,7 +188,7 @@ static __always_inline void *lz77_encode_match(void *dst, void **nib, u16 dist, > * MS-XCA 2.3.4 "Plain LZ77 Compression Algorithm Details" - "Processing" > */ > static __always_inline void *lz77_encode_literals(const void *start, const void *end, void *dst, >- long *f, u32 *fc, void **fp) >+ u32 *f, u32 *fc, void **fp) > { > if (start >= end) > return dst; >@@ -201,7 +201,10 @@ static __always_inline void *lz77_encode_literals(const void *start, const void > dst += len; > start += len; > >- *f <<= len; >+ if (len == LZ77_FLAG_MAX) >+ *f = 0; >+ else >+ *f <<= len; > *fc += len; > if (*fc == LZ77_FLAG_MAX) { > lz77_write32(*fp, *f); >@@ -225,7 +228,7 @@ noinline int smb_lz77_compress(const void *src, const u32 slen, > const void *srcp, *rlim, *end, *anchor; > u32 *htable, hash, flag_count = 0; > void *dstp, *nib, *flag_pos; >- long flag = 0; >+ u32 flag = 0; > > /* This is probably a bug, so throw a warning. */ > if (WARN_ON_ONCE(*dlen < smb_lz77_compressed_alloc_size(slen))) >@@ -327,9 +330,13 @@ noinline int smb_lz77_compress(const void *src, const u32 slen, > out: > dstp = lz77_encode_literals(anchor, end, dstp, &flag, &flag_count, &flag_pos); > >- flag_count = LZ77_FLAG_MAX - flag_count; >- flag <<= flag_count; >- flag |= (1UL << flag_count) - 1; >+ if (flag_count) { >+ flag_count = LZ77_FLAG_MAX - flag_count; >+ flag <<= flag_count; >+ flag |= (1U << flag_count) - 1; >+ } else { >+ flag = ~0U; >+ } > lz77_write32(flag_pos, flag); > > *dlen = dstp - dst; >-- >2.53.0 >