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tracefs: Avoid changing i_mode to a temp value
Right now inode->i_mode is updated twice to reach the desired value in tracefs_apply_options(). Because there is no lock protecting the two writes, other threads might read the intermediate value of inode->i_mode. Thread-1 Thread-2 // tracefs_apply_options() //e.g., acl_permission_check inode->i_mode &= ~S_IALLUGO; unsigned int mode = inode->i_mode; inode->i_mode |= opts->mode; I think there is no need to introduce a lock but it is better to only update inode->i_mode ONCE, so the readers will either see the old or latest value, rather than an intermediate/temporary value. Note, the race is not a security concern as the intermediate value is more locked down than either the start or end version. This is more just to do the conversion cleanly. Link: https://lore.kernel.org/linux-trace-kernel/AB5B0A1C-75D9-4E82-A7F0-CF7D0715587B@gmail.com Signed-off-by: Sishuai Gong <sishuai.system@gmail.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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1 changed files with 4 additions and 2 deletions
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@ -310,6 +310,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount)
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struct tracefs_fs_info *fsi = sb->s_fs_info;
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struct inode *inode = d_inode(sb->s_root);
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struct tracefs_mount_opts *opts = &fsi->mount_opts;
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umode_t tmp_mode;
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/*
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* On remount, only reset mode/uid/gid if they were provided as mount
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@ -317,8 +318,9 @@ static int tracefs_apply_options(struct super_block *sb, bool remount)
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*/
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if (!remount || opts->opts & BIT(Opt_mode)) {
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inode->i_mode &= ~S_IALLUGO;
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inode->i_mode |= opts->mode;
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tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
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tmp_mode |= opts->mode;
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WRITE_ONCE(inode->i_mode, tmp_mode);
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}
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if (!remount || opts->opts & BIT(Opt_uid))
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