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[223.24.162.214]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3276f6a6cb3sm2214219a91.9.2025.08.27.07.20.33 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Aug 2025 07:20:34 -0700 (PDT) Date: Wed, 27 Aug 2025 21:20:26 +0700 From: Egor Shestakov To: linux-fsdevel@vger.kernel.org Subject: [BUG] f2fs-tools: fsck infinite loop in options parsing Message-ID: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hi! I found a bug in the fsck.f2fs that cause infinite loop in f2fs_parse_options(). To reproduce it you can call program with a '-py' united options combination, but when it's separate '-p -y' works well. Simply execute `./f2fs.fsck -py` to catch the bug. Buggy part of a fsck/main.c code (unchanged since 2018): > case 'p': > /* preen mode has different levels: > * 0: default level, the same as -a > * 1: check meta > * 2: same as 0, but will skip some > * check for old kernel > */ > if (optarg[0] == '-' || !is_digits(optarg) || > optind == argc) { > MSG(0, "Info: Use default preen mode\n"); > c.preen_mode = PREEN_MODE_0; > c.auto_fix = 1; > optind--; > break; > } The bug occurs when a case 'p' match and after it there is not suitable argument so a decrement optind-- happened. Since the option '-p' united with its argument a getopt increments optind only by one, not by two, as expected. Therefore it enters to infinite loop. I couldn't find good solution. Changing a preen level options semantic is impossible because breaks many scripts, for example in initrd. Possible solution is use a two colons in optstring that means optinal argument, but this is a GNU extension, so not all standard libraries support it, in particular Musl. -- Egor Shestakov vedingrot ascii(0x40) gmail ascii(0x2E) com