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Thu, 20 Oct 2022 16:17:23 -0700 (PDT) From: Hawkins Jiawei To: syzbot+a3e6acd85ded5c16a709@syzkaller.appspotmail.com, Mike Kravetz , Muchun Song Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, 18801353760@163.com, yin31149@gmail.com Subject: [PATCH -next] hugetlbfs: fix null-ptr-deref in hugetlbfs_parse_param() Date: Fri, 21 Oct 2022 07:16:08 +0800 Message-Id: <20221020231609.4810-1-yin31149@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666307855; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=C+z4UK+YSd44EWa9tT929JkG3rIhRX9wOtAF4K/xipQ=; b=2mSFZMVKiYb9E8MsrnYdV/OfVcQWBjQC/CoRSJzdcGivjuIfKojAtH6R8W3LKKGDFf/iNz ziwubN5lcIn9I+OeOq75I61EvaP1Qwi/L1FHzP64WDkRYt0DPdpVtlQv7BkYS0PK3YTFPE o2hxKS+xWTzNGkwxaDgakdLVJfnf5+g= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=Fz+yVYwn; spf=pass (imf21.hostedemail.com: domain of yin31149@gmail.com designates 209.85.222.51 as permitted sender) smtp.mailfrom=yin31149@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666307855; a=rsa-sha256; cv=none; b=whROfjGwaPmgV13YysFYa5KayPrDvQusghUPftd/aIuMETU6TM46UaPnzOtgIR5ZLogNoh PFHxF4KZJp6w9kBcMNGEap3EsRi3hdke9H4rUGaNviyQxOWP/u4vFwk5ih7syD0b7nnsYi LysbuQ5N+xlWUTzzaXktp5bQ8jweyCg= Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=Fz+yVYwn; spf=pass (imf21.hostedemail.com: domain of yin31149@gmail.com designates 209.85.222.51 as permitted sender) smtp.mailfrom=yin31149@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: EDD151C002A X-Stat-Signature: zahcbu1zeok91deupdp6ii8kybnzhq74 X-Rspam-User: X-HE-Tag: 1666307854-804002 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Syzkaller reports a null-ptr-deref bug as follows: ====================================================== KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:hugetlbfs_parse_param+0x1dd/0x8e0 fs/hugetlbfs/inode.c:1380 [...] Call Trace: vfs_parse_fs_param fs/fs_context.c:148 [inline] vfs_parse_fs_param+0x1f9/0x3c0 fs/fs_context.c:129 vfs_parse_fs_string+0xdb/0x170 fs/fs_context.c:191 generic_parse_monolithic+0x16f/0x1f0 fs/fs_context.c:231 do_new_mount fs/namespace.c:3036 [inline] path_mount+0x12de/0x1e20 fs/namespace.c:3370 do_mount fs/namespace.c:3383 [inline] __do_sys_mount fs/namespace.c:3591 [inline] __se_sys_mount fs/namespace.c:3568 [inline] __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd [...] ====================================================== According to commit ac369cdd9448("vfs: parse: deal with zero length string value"), kernel will sets the param->string to null pointer in vfs_parse_fs_string() if fs string has zero length. Yet the problem is that, hugetlbfs_parse_param() will dereference the param->string, without checking whether it is a null pointer. To be more specific, if hugetlbfs_parse_param() parses an illegal mount parameter, such as "size=,", kernel will constructs struct fs_parameter with null pointer in vfs_parse_fs_string(), then passes this struct fs_parameter to hugetlbfs_parse_param(), which triggers the above null-ptr-deref bug. This patch solves it by adding sanity check on param->string in hugetlbfs_parse_param(). Reported-by: syzbot+a3e6acd85ded5c16a709@syzkaller.appspotmail.com Tested-by: syzbot+a3e6acd85ded5c16a709@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/0000000000005ad00405eb7148c6@google.com/ Signed-off-by: Hawkins Jiawei --- fs/hugetlbfs/inode.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 7f836f8f9db1..3ee84604e36d 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -1377,7 +1377,7 @@ static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *par case Opt_size: /* memparse() will accept a K/M/G without a digit */ - if (!isdigit(param->string[0])) + if (!param->string || !isdigit(param->string[0])) goto bad_val; ctx->max_size_opt = memparse(param->string, &rest); ctx->max_val_type = SIZE_STD; @@ -1387,7 +1387,7 @@ static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *par case Opt_nr_inodes: /* memparse() will accept a K/M/G without a digit */ - if (!isdigit(param->string[0])) + if (!param->string || !isdigit(param->string[0])) goto bad_val; ctx->nr_inodes = memparse(param->string, &rest); return 0; @@ -1403,7 +1403,7 @@ static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *par case Opt_min_size: /* memparse() will accept a K/M/G without a digit */ - if (!isdigit(param->string[0])) + if (!param->string || !isdigit(param->string[0])) goto bad_val; ctx->min_size_opt = memparse(param->string, &rest); ctx->min_val_type = SIZE_STD; -- 2.25.1