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Message-Id: <1380659178-28605-10-git-send-email-tixxdz@opendz.org> Date: Tue, 1 Oct 2013 21:26:18 +0100 From: Djalal Harouni <tixxdz@...ndz.org> To: "Eric W. Biederman" <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, "Serge E. Hallyn" <serge.hallyn@...ntu.com>, Cyrill Gorcunov <gorcunov@...nvz.org>, David Rientjes <rientjes@...gle.com>, LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org, kernel-hardening@...ts.openwall.com Cc: tixxdz@...il.com, Djalal Harouni <tixxdz@...ndz.org> Subject: [PATCH v2 9/9] procfs: improve permission checks on /proc/*/syscall Permission checks need to happen during each system call. Therefore we need to convert the /proc/*/syscall entry from an INF node to a REG node. Doing this will make /proc/*/syscall have its own file operations to implement appropriate checks and avoid breaking shared INF file operations. Add the syscall_open() to check if the file's opener has enough permission to ptrace the task during ->open(). Add the syscall_read() to check permissions and to read task syscall information. If the classic ptrace_may_access() check is passed, then check if current's cred have changed between ->open() and ->read(), if so, call proc_allow_access() to check if the original file's opener had enough permissions to read the task syscall info. This will block passing the file descriptor to a more privileged process. For readability split code into another task_syscall_read() function which is used to get the syscall entries of the task. Cc: Kees Cook <keescook@...omium.org> Cc: Eric W. Biederman <ebiederm@...ssion.com> Signed-off-by: Djalal Harouni <tixxdz@...ndz.org> --- fs/proc/base.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 84 insertions(+), 9 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index b80588a..f98889d 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -150,6 +150,9 @@ struct pid_entry { NULL, &proc_single_file_operations, \ { .proc_show = show } ) +/* 4K page size but our output routines use some slack for overruns */ +#define PROC_BLOCK_SIZE (3*1024) + /** * proc_same_open_cred - Check if the file's opener cred matches the * current cred. @@ -678,13 +681,32 @@ static int proc_pid_limits(struct task_struct *task, char *buffer) } #ifdef CONFIG_HAVE_ARCH_TRACEHOOK -static int proc_pid_syscall(struct task_struct *task, char *buffer) +static int syscall_open(struct inode *inode, struct file *filp) +{ + int err = -ESRCH; + struct task_struct *task = get_proc_task(file_inode(filp)); + + if (!task) + return err; + + err = mutex_lock_killable(&task->signal->cred_guard_mutex); + if (err) + goto out; + + if (!ptrace_may_access(task, PTRACE_MODE_ATTACH)) + err = -EPERM; + + mutex_unlock(&task->signal->cred_guard_mutex); +out: + put_task_struct(task); + return err; +} + +static int task_syscall_read(struct task_struct *task, char *buffer) { + int res; long nr; unsigned long args[6], sp, pc; - int res = lock_trace(task); - if (res) - return res; if (task_current_syscall(task, &nr, args, 6, &sp, &pc)) res = sprintf(buffer, "running\n"); @@ -696,9 +718,64 @@ static int proc_pid_syscall(struct task_struct *task, char *buffer) nr, args[0], args[1], args[2], args[3], args[4], args[5], sp, pc); - unlock_trace(task); + return res; } + +static ssize_t syscall_read(struct file *file, char __user *buf, + size_t count, loff_t *ppos) +{ + int same_cred; + ssize_t length; + unsigned long page; + const struct cred *fcred = file->f_cred; + struct inode *inode = file_inode(file); + struct task_struct *task = get_proc_task(inode); + + length = -ESRCH; + if (!task) + return length; + + if (count > PROC_BLOCK_SIZE) + count = PROC_BLOCK_SIZE; + + length = -ENOMEM; + page = __get_free_page(GFP_TEMPORARY); + if (!page) + goto out; + + same_cred = proc_same_open_cred(fcred); + + length = lock_trace(task); + if (length) + goto out_free; + + if (!same_cred && + !proc_allow_access(fcred, task, PTRACE_MODE_ATTACH)) { + length = -EPERM; + unlock_trace(task); + goto out_free; + } + + length = task_syscall_read(task, (char *)page); + unlock_trace(task); + + if (length >= 0) + length = simple_read_from_buffer(buf, count, ppos, + (char *)page, length); + +out_free: + free_page(page); +out: + put_task_struct(task); + return length; +} + +static const struct file_operations proc_pid_syscall_operations = { + .open = syscall_open, + .read = syscall_read, + .llseek = generic_file_llseek, +}; #endif /* CONFIG_HAVE_ARCH_TRACEHOOK */ /************************************************************************/ @@ -789,8 +866,6 @@ static const struct inode_operations proc_def_inode_operations = { .setattr = proc_setattr, }; -#define PROC_BLOCK_SIZE (3*1024) /* 4K page size but our output routines use some slack for overruns */ - static ssize_t proc_info_read(struct file * file, char __user * buf, size_t count, loff_t *ppos) { @@ -2760,7 +2835,7 @@ static const struct pid_entry tgid_base_stuff[] = { #endif REG("comm", S_IRUGO|S_IWUSR, proc_pid_set_comm_operations), #ifdef CONFIG_HAVE_ARCH_TRACEHOOK - INF("syscall", S_IRUSR, proc_pid_syscall), + REG("syscall", S_IRUSR, proc_pid_syscall_operations), #endif INF("cmdline", S_IRUGO, proc_pid_cmdline), ONE("stat", S_IRUGO, proc_tgid_stat), @@ -3096,7 +3171,7 @@ static const struct pid_entry tid_base_stuff[] = { #endif REG("comm", S_IRUGO|S_IWUSR, proc_pid_set_comm_operations), #ifdef CONFIG_HAVE_ARCH_TRACEHOOK - INF("syscall", S_IRUSR, proc_pid_syscall), + REG("syscall", S_IRUSR, proc_pid_syscall_operations), #endif INF("cmdline", S_IRUGO, proc_pid_cmdline), ONE("stat", S_IRUGO, proc_tid_stat), -- 1.7.11.7
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