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Ts'o" To: syzbot Cc: adilger.kernel@dilger.ca, akpm@linux-foundation.org, dan.j.williams@intel.com, jack@suse.cz, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: Re: BUG: unable to handle kernel NULL pointer dereference in generic_perform_write (2) Message-ID: <20200415043553.GH90651@mit.edu> References: <00000000000016a67305a33a11f7@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <00000000000016a67305a33a11f7@google.com> 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: #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 5b8b9d0c6d0e0f1993c6c56deaf9646942c49d94 diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 9728e7b0e84f..e44fee317965 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1728,6 +1728,7 @@ static int clear_qf_name(struct super_block *sb, int qtype) #define MOPT_NO_EXT3 0x0200 #define MOPT_EXT4_ONLY (MOPT_NO_EXT2 | MOPT_NO_EXT3) #define MOPT_STRING 0x0400 +#define MOPT_NO_REMOUNT 0x0800 static const struct mount_opts { int token; @@ -1777,7 +1778,7 @@ static const struct mount_opts { {Opt_min_batch_time, 0, MOPT_GTE0}, {Opt_inode_readahead_blks, 0, MOPT_GTE0}, {Opt_init_itable, 0, MOPT_GTE0}, - {Opt_dax, EXT4_MOUNT_DAX, MOPT_SET}, + {Opt_dax, EXT4_MOUNT_DAX, MOPT_SET | MOPT_NO_REMOUNT}, {Opt_stripe, 0, MOPT_GTE0}, {Opt_resuid, 0, MOPT_GTE0}, {Opt_resgid, 0, MOPT_GTE0}, @@ -1819,7 +1820,7 @@ static const struct mount_opts { {Opt_jqfmt_vfsv1, QFMT_VFS_V1, MOPT_QFMT}, {Opt_max_dir_size_kb, 0, MOPT_GTE0}, {Opt_test_dummy_encryption, 0, MOPT_GTE0}, - {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET}, + {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET | MOPT_NO_REMOUNT}, {Opt_err, 0, 0} }; @@ -1917,6 +1918,12 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token, "Mount option \"%s\" incompatible with ext3", opt); return -1; } + if ((m->flags & MOPT_NO_REMOUNT) && is_remount) { + ext4_msg(sb, KERN_ERR, + "Mount option \"%s\" not supported when remounting", + opt); + return -1; + } if (args->from && !(m->flags & MOPT_STRING) && match_int(args, &arg)) return -1; @@ -5429,18 +5436,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) } } - if ((sbi->s_mount_opt ^ old_opts.s_mount_opt) & EXT4_MOUNT_NO_MBCACHE) { - ext4_msg(sb, KERN_ERR, "can't enable nombcache during remount"); - err = -EINVAL; - goto restore_opts; - } - - if ((sbi->s_mount_opt ^ old_opts.s_mount_opt) & EXT4_MOUNT_DAX) { - ext4_msg(sb, KERN_WARNING, "warning: refusing change of " - "dax flag with busy inodes while remounting"); - sbi->s_mount_opt ^= EXT4_MOUNT_DAX; - } - if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED) ext4_abort(sb, EXT4_ERR_ESHUTDOWN, "Abort forced by user");