proc: make sure mem_open() doesn't pin the target's memory
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.
Cc: stable@kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
572d34b946
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@ -711,6 +711,13 @@ static int mem_open(struct inode* inode, struct file* file)
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if (IS_ERR(mm))
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return PTR_ERR(mm);
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if (mm) {
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/* ensure this mm_struct can't be freed */
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atomic_inc(&mm->mm_count);
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/* but do not pin its memory */
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mmput(mm);
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}
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/* OK to pass negative loff_t, we can catch out-of-range */
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file->f_mode |= FMODE_UNSIGNED_OFFSET;
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file->private_data = mm;
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@ -734,6 +741,9 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
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return -ENOMEM;
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copied = 0;
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if (!atomic_inc_not_zero(&mm->mm_users))
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goto free;
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while (count > 0) {
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int this_len = min_t(int, count, PAGE_SIZE);
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@ -761,6 +771,8 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
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}
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*ppos = addr;
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mmput(mm);
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free:
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free_page((unsigned long) page);
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return copied;
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}
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@ -797,7 +809,7 @@ static int mem_release(struct inode *inode, struct file *file)
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{
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struct mm_struct *mm = file->private_data;
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if (mm)
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mmput(mm);
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mmdrop(mm);
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return 0;
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}
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