From 0053779e04bbfabe31287245d89ad10bb66e758a Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 31 Jan 2012 17:15:11 +0100 Subject: proc: make sure mem_open() doesn't pin the target's memory commit 6d08f2c7139790c268820a2e590795cb8333181a upstream. Once /proc/pid/mem is opened, the memory can't be released until mem_release() even if its owner exits. Change mem_open() to do atomic_inc(mm_count) + mmput(), this only pins mm_struct. Change mem_rw() to do atomic_inc_not_zero(mm_count) before access_remote_vm(), this verifies that this mm is still alive. I am not sure what should mem_rw() return if atomic_inc_not_zero() fails. With this patch it returns zero to match the "mm == NULL" case, may be it should return -EINVAL like it did before e268337d. Perhaps it makes sense to add the additional fatal_signal_pending() check into the main loop, to ensure we do not hold this memory if the target task was oom-killed. Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/proc/base.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/proc/base.c b/fs/proc/base.c index 49b82beec31..22794e8ab99 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -775,6 +775,13 @@ static int mem_open(struct inode* inode, struct file* file) if (IS_ERR(mm)) return PTR_ERR(mm); + if (mm) { + /* ensure this mm_struct can't be freed */ + atomic_inc(&mm->mm_count); + /* but do not pin its memory */ + mmput(mm); + } + /* OK to pass negative loff_t, we can catch out-of-range */ file->f_mode |= FMODE_UNSIGNED_OFFSET; file->private_data = mm; @@ -798,6 +805,9 @@ static ssize_t mem_rw(struct file *file, char __user *buf, return -ENOMEM; copied = 0; + if (!atomic_inc_not_zero(&mm->mm_users)) + goto free; + while (count > 0) { int this_len = min_t(int, count, PAGE_SIZE); @@ -825,6 +835,8 @@ static ssize_t mem_rw(struct file *file, char __user *buf, } *ppos = addr; + mmput(mm); +free: free_page((unsigned long) page); return copied; } @@ -861,7 +873,7 @@ static int mem_release(struct inode *inode, struct file *file) { struct mm_struct *mm = file->private_data; if (mm) - mmput(mm); + mmdrop(mm); return 0; } -- cgit v1.2.3-18-g5258