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Thu, 24 Sep 2026 06:37:52 -0700 (PDT) Received: from localhost.localdomain ([94.240.182.136]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fe5b9f253sm77377825e9.1.2026.09.24.06.37.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 06:37:51 -0700 (PDT) From: Svyatoslav Nikolenko To: jaegeuk@kernel.org, chao@kernel.org Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, Svyatoslav Nikolenko , syzbot+dfcbc1741488709db4b2@syzkaller.appspotmail.com Subject: [PATCH] f2fs: check log_blocksize bounds in __f2fs_commit_super Date: Thu, 24 Sep 2026 16:37:25 +0300 Message-ID: <20260924133726.2250-1-nsvatoslav515@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Syzbot reported a shift-out-of-bounds panic in SECTOR_FROM_BLOCK() during superblock writeback via __f2fs_commit_super(). When mounting a corrupted filesystem image where log_blocksize is set to 0, f2fs attempts to perform recovery or commit the superblock status. SECTOR_FROM_BLOCK() relies on F2FS_LOG_SECTORS_PER_BLOCK(sbi), which evaluates to (sbi->log_blocksize - 9). When log_blocksize is 0, this calculates 0 - 9 = -9, causing an unsigned underflow (4294967287) and triggering a UBSAN shift out-of-bounds error when shifting sector addresses. Fix this by validating sbi->log_blocksize at the top of __f2fs_commit_super() and returning -EFSCORRUPTED if it is less than 9 (the minimum valid sector shift exponent). Reported-by: syzbot+dfcbc1741488709db4b2@syzkaller.appspotmail.com Tested-by: syzbot+dfcbc1741488709db4b2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=dfcbc1741488709db4b2 Signed-off-by: Svyatoslav Nikolenko --- fs/f2fs/super.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c index 6a2f09c61dcd..b6b32bcbc126 100644 --- a/fs/f2fs/super.c +++ b/fs/f2fs/super.c @@ -3934,6 +3934,9 @@ static int __f2fs_commit_super(struct f2fs_sb_info *sbi, struct folio *folio, blk_opf_t opf = REQ_OP_WRITE | REQ_SYNC | REQ_PREFLUSH | REQ_FUA; int ret; + if (unlikely(sbi->log_blocksize < 9)) + return -EFSCORRUPTED; + folio_lock(folio); folio_wait_writeback(folio); if (update) -- 2.47.3